Category Archives: horticulture

A diatribe against landscape fabric

In an era of rising eco-consciousness, homeowners are gradually moving away from lawns and other heavily irrigated landscapes.

The trend is toward xeriscapes, landscapes that are designed for climate they are located in, with plants adapted to thrive on little more than rainfall, and gardens that use efficient irrigation systems like drip systems or, in some cases, no irrigation at all. That is definitely a laudable option in my book—when I install gardens, it’s practically the only thing I consider unless I’m asked to do otherwise. Not only is it better for the environment, a site-appropriate garden is more resilient and easier to maintain.

But one unfortunate detour in the path towards xeriscaping is a tendency for installers to plot out gardens with vast swaths of landscape fabric. The material, made of polypropylene plastic, is spun into threads or ribbons and woven into a cloth purported to allow air and water through, then topped with gravel or mulch. The stated purpose of the fabric is to prevent weeds from emerging between the plants, which, in a popular xeriscape style, are placed relatively far apart in holes punched strategically in the fabric.

It’s a no from me

There are a number of low-water garden plants that appear to do ok in landscape fabric, and you have seen them because they are the popular plants to install in road medians and around parking lots, or other rarely-maintained but busy public spaces, where landscape fabric is ubiquitous, or at least has been for a couple decades at the time I am writing this. And indeed, for the first year—or at least at the moment that the installation service collects payment from the property owner—it appears that the fabric is doing its job keeping plants comfortably spaced and blocking the weeds between them.

Many modern xeriscape styles, especially those I see around Denver, seem to exist on the idea of saving water by using a lack of plants. The few that are in place consist of some yucca or a small patch of daylilies, a fernleaf yarrow or two, some sedums, a couple stands of ‘Karl Forster’ ornamental grass, and a big patch of Russian sage, all arranged as islands in a sea of gravely rock. The absence of plant coverage means weeds would have ample opportunity to grow, but are kept at bay, at first, by the fabric beneath them.

That’s not the case the year after. Again, you have seen this before—how often do the gardens around the edges of parking lots keep looking great for long? There are always weeds, and probably a few patches where installed plants have died, and the opening is crammed with cheatgrass because the drip emitter is still trickling water in that spot. Even an untended irrigation ditch or rural highway shoulder, receiving no planting or maintenance whatsoever, probably has prettier vegetation than the berms around a suburban parking lot, middle school yard or boulevard median, where fabric is purportedly keeping things nice. Some lucky properties might get a second or third year out of their fabric, but ultimately, inevitably, the fabric will fail, and the garden will go to chaos unless it’s in an affluent area where it is frequently re-installed.

Ironically, a garden bed covered in landscape fabric is like a curated space for noxious weeds

The types of weeds that we have learned to dread most as gardeners are species that have followed human inhabitation around the world—as invasive species, thriving on the peculiar alterations we repeatedly make to land.

Despite the wide variety of weed species we deal with, there are actually some pronounced ecological similarities between the most common garden weeds. They usually resent shade and do not thrive in competition from diverse neighboring plants, but spread eagerly in monocultures like lawns or crop fields or areas cleared by frequent mowing, herbicides, foot traffic or construction. Common weeds are resistant to chemicals that kill other plants, mainly because they have all been sprayed so many times and only the survivors, bearing genetic mutations for resistance, have passed on their seeds. Common weeds dominate dense compacted soils low in oxygen—humans are great at creating these compacted soils along streets, in lawns, in foot-trafficked areas and construction sites—and are tolerant of salt and other common pollutants found in developed areas.

The weeds germinate in two main phases depending on the species—late winter, when nothing else in the garden is active (we don’t often think of this time as meaningful for plant growth, though it is in the wild), or at the onset of hot temperatures in late spring when long days supercharge fast growth. The weeds reach maturity within a few weeks, faster than most other plants do, as a function of the frequently-disturbed settings they are adapted to. They quickly flower and drop more seed, or anchor their roots into deep soil before anything else can displace them.

These weeds—you know them as bindweed, dandelions, thistle, quackgrass, cheatgrass, sorrel and others—are good at overcoming the barrier weed fabric presents to them. They can germinate in the duff layer on top of the fabric and grow in soils that are extremely shallow (such as cheatgrass), or they send their taproots down through the fabric (examples include mallow or curly dock), or they manage to gain foothold under the barrier and spread on long runners that can grow several feet in all directions, searching for an opening. Bindweed and thistle are obvious examples of weeds that advance underground, exploit seams or holes in the fabric, and, left unchecked, can form dense mats on top of it with deep, unreachable roots burrowed in the low-oxygen soils beneath. Meanwhile, desirable plants—many of which can be quite hardy in the face of competition or drought—do not contend well with the surface barrier, and can’t fill in to displace the weeds. Groundcovers are limited to the size of the hole in the fabric that was cut for them, so they more resemble cute miniature plants than the sprawling spreaders they are selected to be.

The above are reasons why landscape fabric doesn’t work as well as we hope it would. But I’d also like to address some ways fabric could be actively harmful, at least in terms of missed opportunity to create a garden with ecological value.

How unnatural barriers block healthy processes in the garden

See, long-lived plants that colonize the soil actually improve it structurally and chemically, to make the soil layers much more porous, absorbent of water and efficient at recycling nutrients. This benefits the plants directly as the soil’s inhabitants, but it also has secondary benefits for the whole system. Plants’ deep roots periodically die and are replaced by new roots, leaving long-lasting channels in the earth, which water can trickle down and oxygen can move through. The leafy and woody debris plants drop on the soil surface feeds microbes that bind silt and clay particles to bits of organic material, forming granules that give soil a grainy, light texture even if the inorganic components are otherwise very fine and sticky. The worms and burrowing insects that feed off of dead leaves and roots stir the soil and make larger channels, crossing the soil profile in many directions.

All of this activity, in aggregate, drags organic material—often referred to in shorthand as carbon—deep into the soil, where it is sequestered for many years, and helps draw heavy rainfall into the deep layers, and also gradually wicks deep water back up towards the surface when the top layers are dry.

All of this further serves to capture heavy rain and hold it on site, or gradually feed water to aquifers, with minimal runoff. Limiting runoff has the obvious effect of reducing flooding, but also means our urban pollutants (mostly nitrates and sulfates) can be processed by soil bacteria and rendered harmless before they reach natural waterways. When land is covered by deep, porous, biologically active soil, streams are fed by rainwater moving through soil over weeks rather than runoff pouring over the land in hours, and thus streams will not swell as intensely in storms or dry to a trickle during brief droughts. Deep, uninterrupted soils also mean that water stays put in deep layers of soil for a long time, and plants can draw from the reserves between rains, so there is less need for irrigation, less loss of plant life during dry spells, and more biological productivity on the whole.

Landscape fabric interferes with all of this. When soil particles mesh with the fabric, it forms a sheet that is far less permeable to water and oxygen than the fabric initially was. Between holes punched in the fabric for plants, the soil surface is relatively lifeless and hard, although lifting a sheet of fabric might reveal the thin, white etiolated stolons of bindweed and Canada thistle corkscrewing in all directions just beneath it.

The benefits of open, mulched soil with no barriers extends to animal life as well. Beneficial insects—both carnivores, which eat other insects, and detritrivores, which eat dead leaves, stems and fungi—overwinter below ground and benefit from free movement between soil and the sky. Small birds, in turn, rely on an abundant supply of earthworms, beetles, grubs and arachnids in the mulch layer. This supply of protein is crucially important for them raise their young, as you will see when they arrive to pick through the garden and burrow into the duff layer with their heads. Soil creatures will also come up to eat dead plant material or to drag it into their burrows to moisten it so they can eat portions as they decay, cleaning up the garden and recycling the nutrients. All of this life and activity depends on a barrier-free continuum between the sky and the soil—two realms that are not really as separate on Earth as they seem.

With this, I hope it’s clear that landscape fabric can cause more problems than it solves. A relatively recent invention, landscape fabric is a strategy that, though logically understandable, doesn’t hold up in practice—like so many of our attempts at micro-managing nature. Instead, using organic mulches like wood chips, or other natural materials such as large stones, can change the structure of a perennial garden favoring desirable plants over opportunistic weeds. In turn, it allows the plants themselves to control their habitat, feeding wildlife and forming a garden that does not deteriorate with time, but grows only more well-established and resilient.

Why snow cover is good for your garden

For those in northern latitudes, winter is a slow time in the garden. Plants are dormant, nursery stores are bare, and for most of the winter it’s still too soon to start your seed trays for the vegetable garden.

But one thing that keeps me active through the winter months is taking advantage of snow. In Denver, a semi-arid region in the rain shadow of the Rocky Mountains, we rarely if ever get deep accumulations. Six inches is a big storm, twelve is massive. It usually melts completely before the next snow. That’s to be expected in a climate with between 10 and 15 inches of precipitation in an entire year. But when the snow comes, I’m ready, heading out to scoop the treasure and pile it in the garden.

How snow protects plants from cold

It’s counter-intuitive that something that is, by definition, frozen, helps protect the garden from winter’s dramatic temperature swings. It comes down to the ways that plants protect their dormant tissues from the destructive power of ice.

Dehydration as protection

Plant cells are mostly water, and for non-adapted plants, ice crystals forming in cells pierce and rupture them. When the plant thaws, the pulverized tissues hang limp like cooked spinach, utterly destroyed.

Cold-adapted plants have a variety of defenses. First and foremost, they prepare for cold by allowing their tissues to dehydrate. They will often do this by moving cellular water to the spaces between cells, where it can freeze safely. Inside the cells, the water becomes thick and syrupy with sugar, electrolytes, peptides and enzymes that interfere with ice crystallization. Instead of freezing at 32 degrees Fahrenheit (0 degrees Celcius) as pure water does, ice in plant cells may not form until the temperature drops to 25 degrees, 20 degrees or lower. (The limit depends on the species, the variety, and how much time the plant has had to prepare for coming frost.) As temperatures continue to drop, more water will migrate outside the cell and freeze, leaving the inside even more dehydrated. Thus, freeze tolerance in many species goes hand in hand with the plant’s ability to cope with drying out.

Eventually, temperatures drop low enough that cell contents freeze, which is lethal to tissues on plants that die to the ground each winter. Those with perennial above-ground tissues may tolerate ice inside the cell. (Cell contents are by now so dehydrated that there’s only so much damage ice crystals can do.) Other kinds of plants retreat to the ground, where the thermal mass of the Earth keeps roots and storage organs within tolerable temperature ranges.

The burdens of sun and wind

Yet, even when plants are able to survive a frozen-solid state, they have additional issues to contend with. Drying winds and sun can loosen frozen water molecules and convert them directly to vapor in a process called sublimation. (Though very tough plants can survive down to 25 or 30 percent water in their tissues, they cannot survive drying out completely.) Oxidation reactions with air can degrade tissues when the frozen plants are unable to produce antioxidant compounds to protect themselves. Ultraviolet light from the sun damages cell organs and DNA. During the growing season, plants are constantly repairing damage from these assaults. But plants can’t heal while frozen, and damage accumulates. Thus it is not just the winter’s minimum temperature but also the length and frequency of hard freezes that determines whether plant tissues are injured beyond a point of no return before spring.

Snow creates a stable, protected environment

Fortunately, most of these issues are ameliorated by snow. Because a layer of snow is mostly air—around 95 percent air after a fresh, fluffy snowfall, and at least 80 percent on old, crusty snow or heavy wet snow—it is an excellent insulator. As temperatures crash below zero outside, they stabilize at around 25 degrees Fahrenheit when measured 4 inches into the snowbank.

Next, snow blocks ultraviolet light, and keeps stems and leaves from drying in a zone of 100 percent relative humidity. Yet despite the moisture, oxygen can diffuse through and most pathogens cannot grow below freezing. Thus, snow cover can keep even fairly tender plant tissues in a state of happy, mostly suspended animation for months on end.

A few bonus benefits of shoveling your sidewalk snow onto the garden

In the Western U.S. we’ve been contending with a gradual drying trend and droughts that get more severe with climate change. At the same time, though temperatures have gotten on average warmer, they also swing more fiercely now. Sudden spring cold snaps injure plants more badly when they’d let down their defenses during a warm spell.

Snow cover helps with both these problems—keeping plants properly chilled through winter, and supplying extra moisture that is happily taken up in spring.

An additional bonus for me is that it protects the environment. Runoff from streets in winter carries pollutants such as sidewalk salts (magnesium, calcium or sodium), fertilizer, oils, nitrates and sulfates. Often, stormwater systems move runoff directly into lakes, rivers and streams. When these substances contact soil, they’re quickly scooped up by soil microbes that convert them into nutrients. Those nutrients are in turn taken up by plants. But urban runoff systems don’t often exploit that step, sending water directly into streams. There, the pollutants are far more harmful, since they interfere with aquatic organisms’ ability to use dissolved oxygen. Thus, I’m helping clean the streets at the same time I protect and fertilize my garden.

Why are there so many dying trees? What emerald ash borer damage looks like and what we learn from it

If you follow news about trees and gardening, you’ve probably been hearing for many years the ominous news of a devastating invasive insect called the emerald ash borer.

The emerald ash borer, a shiny green beetle destroying ash trees across North America, emerges fron a D-shaped burrow in ash tree trunks in early spring.

History of the emerald ash borer in North America

Ash trees are—or were—one of the most common tree types in North America. Our native ash species include green ash, black ash, white ash and a few others, with extensive natural ranges as one of the most dominant tree caregories in the eastern U.S. They’re also popular in yards for their dense shade and tolerance against late cold snaps, summer heat, periodic drought, and soil compaction found in developed areas or under pavement.

Ash trees, a genus with many species, grow wild across an extensive range spanning North America, particularly in the eastern part of the continent. Additionally, ash trees are one of the most common trees planted in urban areas.

In addition to the North American ash species, there are other ash tree species found around the world, including northwestern Asia where ash trees have contended with the emerald ash borer for millennia. The trees co-evolved with the beetles, making the trees resistant to severe infestation just as the beetles became completely dependent on the ash trees to complete their life cycle.

The pill-shaped, iridescent green flying beetle lays its eggs on bark. The larvae burrow beneath to feed on the carbohydrate-rich cambium layer, the green living tissue just under the bark that lays down new growth rings each year and carries sugars from leaves to roots.

After growing beneath the bark until fall, emerald ash borer grubs pupate through winter and emerge as beetles to infest other ash trees. When a beetle finds a fitting ash tree host, it produces pheromones to attract many others to come in, overwhelming the tree’s ability to drown them out with sticky sap.

In ash trees with no resistance to the emerald ash borer, the larvae burrow so extensively under the bark that they completely cut off the flow of carbohydrates through the vascular system to the roots.

Asian ash trees have long adapted to the presence of the borer; North American trees have their own species of slower-growing borers that can damage but rarely kill the trees. Asian ash trees survive infestation from the more aggressive borer species by producing chemicals that slow the insects’ digestion and thus slow their growth, among other adaptations. That way, they can create new tissue faster than the borers eat it, and achieve a healthy equilibrium with the beetles.

North American ash trees have no resistance to the Asian beetles, so when the first infestation was discovered in Michigan in 2002, it set off sirens for ecologists concerned about the future of several vitally important tree species.

The borer population exploded. Within years, ash tree forests across the Midwest and eastern Canada were wiped out. Entire pure stands of ash were converted into shrubby meadows, with ominous dead gray trunks standing over them, as if a wildfire had burned through. Shortly after, mixed forests lost their ash tree stocks. Traveling a few miles per year, the borers spread throughout the region, and occasionally hitchhiked on firewood or other human transport to arrive in other portions of the continent.

Ash borers invading the continent have resulted in vast swaths of dead forests in the Eastern U.S. and Canada.

Infestations in Boulder County, Colorado began several years ago, initiating a government quarantine against ash wood products being moved from Boulder to Denver or beyond. But when the borers were identified in the northern Denver suburbs in 2019, the quarantine was retired since there was now no way to stop them from flying tree to tree and infiltrating the entire metro area.

The documented extent of emerald ash borers in North America as of summer 2020.

In 2021, this is the first summer we’ve seen extensive damage to virtually all of the untreated ash trees in the region. While it’s uncommon to see adult beetles, the signs are impossible to miss.

How ash borers kill ash trees, and how to identify the damage

Emerald ash borers destroy the part of the tree that carries sugar from the leaves down to the roots (the outer layer of cambium or phloem), but they do not stop water from rising from the roots to the leaves, which travels through nonliving tissue (xylem) in the inner cambium. Because the xylem carries only water and minerals, it doesn’t have the carbohydrates borers need to grow and the grubs won’t eat it. That means that the tree can produce leaves for a while even after the infestation is advanced.

But without phloem to carry sugars made in the leaves down to the roots, the entire root system begins starving. It is unable to produce an adequate number of annual feeder roots that sprout from the larger woody roots. Unlike other tree diseases that may kill a section of the canopy at a time, the entire tree’s system for staying alive begins to fail. The appearance is similar to a tree that has a girdling root, or is being girdled by a grate or has experienced other extensive damage to the roots: the canopy thins from the top down and starts retreating.

An ash tree with an advanced ash borer infestation has already suffered extensive damage to roots, starved because the insects have cut their supply of energy from leaves. The canopy, in turn, dies back from the top to try to achieve a more manageable size. It happens on all branches at the same time rather than in sections, which would be a sign of a different kind of pathogen.

During the first season, an ash borer infestation can go completely unnoticed. The first subtle sign is either woodpeckers showing an unusual interest in the tree or small, D-shaped holes in the bark where the first generation of beetles hatched out to mate and lay more eggs.

Trees that are already catastrophically damaged by ash borer can continue to produce dwindling leaves for a year or two because the part of the circulatory system that carries water—located deeper in non-living wood—is still intact. But there’s no hormone communication between the roots and leaves, and no sugar making its way down to feed the roots. Soon, the roots die back and reduce their ability to absorb enough water for the whole tree at its current size.

A tree with inadequate roots, no matter the cause, thins out at the top (which is the the most distant point for water and hormones produced by roots to reach). Trees cope with severe root loss by trying to restructure themselves: they sacrifice leaves and branches that are no longer getting enough water and nutrients to photosynthesize, which starts at the top. Ash trees will produce new green shoots from large branches or trunk, and the new growths can be very vigorous and dense. However, their vigor is deceptive since the total number of leaves is much lower. This would effectively make a smaller tree, which in some scenarios would return to balance with the weakened root system and allow the canopy to regenerate, albeit with a very poor branch structure.

Unfortunately, in the case of an ash borer infestation, these attempts at restructuring the canopy are futile—the root system is not going to rebound since it has been separated from the canopy by ash borer tunnels. The root system is already dying by the time the top level of branches is completely bare.

Usually, the severe damage becomes obvious in late spring when higher portions of an ash tree will fail to leaf out or the tender new leaves die off shortly thereafter. You don’t see much progression in the middle of the growing season since the dying roots can continue to provide a limited water supply to lower leaves. Meanwhile, chunks of bark may begin to curl back or fall off since there’s nothing attaching them to the underlying wood.

You also don’t see much severe wilting and browning in the canopy from ash borer. Browning and singing of the leaves, which occurs, for example, in apple and pear trees affected by diseases like fire blight, suggests a cause that is affecting the ability for water to reach the leaves through xylem. Xylem exist below the upper cambium in channels made of columns of cells that have died and become like hollow straws (the wood’s grain). Bacteria or fungal diseases exist as single cells or filaments that are one cell wide, so they can grow right into the water-carrying xylem channels and shut them off. Infected twigs and branches wilt and turn brown in days.

But because the xylem on infested ash trees are still intact, leaves stay hydrated and don’t yellow or wilt dramatically. Yet, the tree, sensing a nonproductive branch, eventually cuts off the water supply to limbs and retreats further down toward its base.

Later stages of ash borer infestation in a tree

Even green shoots from the base of a mature ash tree infected by emerald ash borer will eventually die as the root system dies, but younger trees, or trees that produce shoots through the soil itself, can form permanent shrubby base growth as they die. The ash borers eventually leave and move on, since they only eat living trunk tissue, and only lay eggs on trunks and branches that are more than a few inches thick.

In trees with basal shoot growth that outlives the dying tree, it’s due to new root systems emerging from the base of each green shoot where they contact moist soil. These bushy, limited growths are vulnerable to drought until the roots grow larger, and they won’t be useful as shade trees. They will only be infested again if they reach a substantial size.

In the last phase of an ash borer infestation, the borers may move on since the part of the trunk they eat is now dead. The tree will produce new shoots from the base, but even these will continue to decline since the root system is so severely starved.

Mature, valuable trees can be protected with systemic insecticides applied before or early in the infestation. But trees that are completely girdled by borers are too far gone even if they still have living portions of canopy, since the roots are dying. Arborists can make a judgment call as to whether the tree is salvageable, usually deeming trees to be too far into the process if the top of the canopy has lost 50 percent or more of a healthy density of leaves.

Asian ash tree species, or hybrids between North American and Asian species, may have enough resistance to ash borers to survive after the first big wave of infestation has passed through a region. Horticulturalists and ecologists are already working hard to develop new ash tree stocks that can resist the borers and potentially restore some of the ash tree options for urban trees. They may even be able to develop strains of native trees to reseed American forests.

Lessons from the emerald ash borer

We as gardeners and tree lovers can take a few valuable lessons from this slow-moving disaster. First and foremost, we need to be conscious of the threat of invasive species. This is not the first time a wave of disease or pest insects threatens to wipe out a major class of North American trees, and since other types of tree epidemics are still making their way around the continent we know it won’t be the last.

Better inspections of plants coming into the U.S. can help, and by carefully observing the environment around us, we may be able to notice, slow down, or eradicate ecological threats before they become unstoppable. County extension offices, which are local branches of state agricultural universities that exist to communicate with the public about landscape health, can be a resource to funnel information to the attention of trained scientists.

A second lesson is to encourage a broader diversity of trees and plants in our urban landscapes. In the recent past, Denver’s urban canopy was dominated by a handful of tree species or families. A loss of one species means a loss of a huge portion of the mature urban canopy, leaving tremendous gaps that take decades to fill with newly-planted trees. By recruiting new species into cultivation (particularly natives in the region), and making sure that each park, yard or city block has several types of trees in it, we can hedge against the chance that a future tree epidemic leaves huge portions of the city bare.

Finally, we can be conscious of the benefits of inviting a diverse array of wildlife into our spaces. Although pests like the ash borer are sometimes unstoppable, they do have natural predators here: woodpeckers, with many native species in this area, eagerly eat emerald ash borer larvae and have actually grown in population in places where the ash borers provide a generous food supply for raising chicks. Other microbes, insects and birds can help compete against current and future destructive pests as long as they have a large enough base population to respond quickly to a major change.

By planting diverse seed-producing gardens, tolerating a moderate amount of native insect pests providing steady food sources, converting rooftops, pavement and gravel strips to open landscapes with lots of region-appropriate plant species, and limiting the use of chemical controls to occasional spot-treatments only, we can create a balanced, abundant urban ecosystem that provides shade and beauty to humans and animals alike, for generations to come.

The meadow garden: where change takes center stage

A meadow garden inverts our common sense of gardening. Instead of cleaning up and simplifying an area, the meadow garden deliberately mimics nature. Instead of arranging plants in grids and rows, the meadow lets them escape and spread. The meadow garden focuses on texture and movement, and is encouraged to change throughout the seasons or the years.

A typical yard has rows or patches of flowers and shrubs around its centerpiece, the lawn. In the meadow garden, it’s the walkways and hardscape that provide structure—as a winding path of cobblestones, a rectangular strip of crushed granite, or a patio. The designer is invited to envision, first, the most appealing way to move through the space. You think about where you’d like to stop or sit, where you’d like to create a focal point, where you want to place a birdhouse or some boulders. The plants cover the remaining area—they are the negative space. In that sense, instead of focusing on the appearance of a garden, a meadow garden focuses on how you will spend time there.

Of course a meadow garden offers many practical rewards as well. Once established it’s very low-maintenance—spreading, rhizomatous or reseeding plants crowd out weeds. Dead stems and flowers provide interesting shapes through the winter so you don’t need to constantly cut things back. The garden provides food for birds and wildlife, hosts a variety of native plants, can be made to require less irrigation, and mulches itself with its falling leaves and stems, gradually improving soil. That might be why this is an increasingly popular garden style for both high-budget public gardens and cost-conscious home gardeners alike.

What is a meadow garden?

Although there is no explicit definition of a meadow garden, meadow gardens typically have the following attributes:

  • Usually covers a larger area than a border garden
  • Grows in full sun to part sun
  • Can be installed with small plants (plugs) and seed, saving costs
  • Makes use of natural rainfall with low to moderate supplemental water
  • Emphasizes grasses, artemisias and textural plants rather than blooming flowers alone
  • Is structured around grassland perennials, plus some annuals that self-seed on their own
  • Tolerates dead flowers, cones and seed pods for visual interests rather than clearing them immediately—a true four-seasons garden
  • Includes plants that are native to the region
  • Considers the plants’ usefulness to birds, wildlife and pollinators
  • Incorporates spreading plants that spread into each other rather than leaving gaps

Creating a meadow garden

Since meadow gardens tend to cover a large area, there are both benefits and challenges. One benefit is that it is more affordable to fill a large space with rapidly-spreading perennials than to do so with slow-growing specimen plants. On the other hand, meadow gardens defy the familiar residential yard structure and require well-placed paths and boundaries to contrast the chaotic nature of the planting beds. Figuring out how to design them well and prepare such a large space for planting can be intimidating.

Planning/designing the garden

Start planning a meadow garden by identifying inhabitable spaces within the garden’s boundaries. If you’d like to include a sitting area, water feature, designated spot for bird feeders, a gazebo or deck, designate those spaces first. Your vision for large shrubs and trees should also come before garden beds. Plant structure and growth in full shade are vastly different and fall under the category of a woodland garden rather than meadow.

  • First step: The borders of the meadow garden are ascertained (in this case the whole yard) and the flagstone patio, seating and fire pit are planned. A winding path is drawn. Solid dark dots represent sprinkler heads in a sprinkler irrigation system.
  • The first order of plants—the tallest flowers and grasses—are designated first. They fill mostly central areas. In most cases, tall plants won’t be close to sprinkler heads where they can block irrigation to other plants.
  • After the largest plants are mapped, shorter plants and spreading plants are plotted, careful to place contrasting shapes and textures side by side.
A hypothetical meadow garden planned in three stages: first hardscape (seating area, trails), then large anchor plants, then smaller fill plants. After that, seed can optionally be sewn over various sections of the garden and additional planting will fill any gaps that materialize.

After you’ve identified your garden’s access points, such as patios or benches, sketch out the walkways between them. Paths can curve, cross or meander, depending on your preference. Straight, square-edged concrete walkways can make an attractive contrast against the billowing drifts of plants, but a crushed stone path that follows a winding arc with flowers and grass spilling over the edge can be beautiful too. It’s also wise to create some narrower, lower-order walkways to divide up large planting beds, for both aesthetic and practical reasons. The secondary paths help you move through the garden without trampling plants, and allow you to enjoy them from different vantage points.

Then, it’s time to figure out the plan for plants. Start by plotting zones for tall, medium and short plants. Site taller plants in the center of planting beds, away from walkways, while shorter plants will line the walkways. Be mindful of views you want to preserve or eyesores you want to screen from various vantage points. Also be mindful of sprinklers: if you have an automatic irrigation system, avoid blocking spray nozzles with tall plants.

Think of flower colors and textures you want to design with. I think it’s best to pick two to three core flower colors per blooming season in a section of the garden and select plants that blooming with various shades of those colors. A few off-theme accent plants can be OK, but sticking to a core color palette will create a much more harmonious and professional look. Arrange large swaths or drifts of many plants of the same species, scaled to the overall garden size. (Enormous gardens may have swaths of tens to hundreds of plants of the same species together, while smallish gardens might only have room for clusters of 2-3 plants). Try to put contrasting textures near each other: grasses next to broad-leafed plants and flowers, plants with sprays of small flowers near plants with large flowers, and plants with silver or purplish leaves beside plants with unremarkable green foliage, and so forth. Consider repeating patterns, with the same species appearing in drifts or clusters in multiple places in the garden rather than a single section for each type of plant.

Clearing the space

What’s the best way to eradicate weeds or lawns to begin planting a garden? Do you need herbicide? Do you need to solarize?Should you till everything up to prepare the soil? I find that less intervention is often quicker and more reasonable: simply covering lawns and weedy areas with a 1/2 to 1-inch layer of compost and then few more inches of cheap, bulk wood chip mulch can smother the grass and create a fertile expanse for a meadow garden to go in.

This meadow garden is being installed in Westminster, Colorado by expanding existing garden beds over a lawn area. I spread a crushed rock path and thin compost layer directly over turf, which, in addition to a 3 inch mulch layer, is sufficient to block sunlight and kill the lawn and weeds. It is immediately ready for plants, as long as grass is removed directly under the plant since the mulch will be parted there. Spring 2020.

If mulching is generally good for gardens, why does covering a lawn or weeds with soil and wood chips kill it?

Simply covering unwanted plants with wood chip mulch can be a surprisingly effective way to weaken and kill them. (Woody shrubs, bindweed, quackgrass, Canada thistle and invasive groundcovers like vinca may be an exception.) Don’t chop the stems off, simply trample them down and cover. Although dormant plants can push spring shoots through mulch and soil to reach sunlight, unwanted plants buried intact during their vegetative phase are often unable to do this. Generating new shoots is a hormonally-driven process in plants—it occurs when there is a loss or absence of existing stems and foliage. Since the weeds and lawn grass still has its vegetation under the mulch—making hormones that signal that the plant still has stems and doesn’t need to create new shoots—weeds wait for daylight that doesn’t come, and exhaust stored energy trying to grow more leaves under the covering.

In most cases, some bits of growth will manage to reach the surface, but they will be weakened, easy to pluck or cover again to deplete them further. Desired plants, on the other hand, have been taking advantage of the fertile season and are prepared to shade and out-compete residual weeds. Occasional light weeding, when vigorous garden plants are becoming established, is enough to tip the balance of power away from weeds and eradicate the majority of them.

In this image I started the process of planting the meadow garden while the lawn was still being covered in compost and mulch. I sacrificed a single, mature Salvia pratensis plant by bare-rooting it and stripping the fibrous main stem into 26 divisions, each with some top growth and connected roots. They were planted directly into the ground under the compost on both sides of the path. 25 of the 26 survived. Spring 2020.

Trails and paths made of crushed stone or sand and flagstone can go right over the weeds and turf as well. (For flagstone or flat pavers, it is better to mow the weeds close to the ground so that the stones don’t shift as the smothered plants decay.)

Just be sure to plant new plants directly in the native soil rather than the pure compost, which will burn tender roots. After a season or two, the compost will break down and merge with the underlying soil.

In this alternate view of the same Westminster, Colorado garden, the lawn is immediately transformed into a clean slate for planting with a top-dressing of compost and mulch. Some of the larger plants had already been growing in the previous garden bed and kept in the new plan. But if you look closely you can see dozens of perennial divisions planted in the area, at very low cost because they were propagated from a handful of fast-growing perennial plants. Spring 2020.

A note on tilling

Tilling is a popular way to clear a garden plot for planting and many guides recommend it as a way to clear beds and “soften” soil for roots. I dispute that. The most aggressive resprouting weeds will return from roots. Soil with existing grass, weeds or other plants is going to be full of beneficial channels where roots have grown and died, worms and burrowing insects have cleared tunnels, and microscopic fungi have built soft fibrous bands of tissue to move water and nutrients around. The existing porosity will allow water to quickly soak into the soil, and new plants’ roots will follow the channels left by old roots to grow deeper more quickly than in compacted soil.

Tilling tends to collapse the soil’s structure. When tilled soil gets wetted again, it becomes muddy and dense. Beyond that, tilling is extra work!

When I plant a small plant or plug, I’ll break up the soil a few inches around the planting hole to remove existing weed roots and make sure soil fines are able to dissolve and settle around the new plant’s roots, but I do not till a broad area. Similarly, when planting seeds, I disrupt the top inch or so of soil to clear competing plants, but don’t go any deeper than that.

This garden is in a residential front yard in Broomfield, Colorado. The homeowner seeded part of the yard with a wildflower and drought-tolerant grass seed mix a few months before I came in to install a more formal meadow garden. After laying crushed stone paths, I began adding yarrow, sedum and lamb’s ear by breaking up the soil in a 12-inch-diameter patch around each new plant so it can establish without competition, and then covered the root zone with mulch. However, some of the grass and flowers can be allowed remain in the gaps to add to this garden.

Planting the garden

A garden doesn’t need to be complete all at once—they take time to mature, and you may be discovering new types of plants you’d like to add in for years to come. But the first plants to install are your big, fast-growing, spreading and reseeding plants, because they will help fill the space, out-compete new or remaining weeds that sprout and give you an immediate reward. You might also be comfortable with letting an aggressive plant, such as lamb’s ear, yarrow or milkweed, spread widely at first, and eventually clear patches of it add new types of plants.

Back in the Westminster garden, young plants are quickly getting established a few months after the original bed was expanded.

Using the same process I used to divide a single Salvia plant into many new plants, I added many other drifts of small plants by splitting up larger plants that had been planted in a nearby garden 1 year earlier. That included fernleaf yarrow (one plant made 15), Stella d’Oro daylilly (one clump made dozens of small clusters around the path edges), lamb’s ear (one clump made a dozen), Rocky Mountain Penstemon (one plant made 15), variegated maidenhair grass (a portion of an old clump made 7), indiangrass (1 clump made 5), little bluestem grass (1 clump made 5), Artemesia ludoviciana (as basal stem cuttings from several plants) and bearded iris (several nearby clusters were divided). There are also 5 nursery-purchased butterfly weed plants, 1 nursery-purchased false indigo, and 3 nursery-purchased anise hyssop. The pink daylilies, Russian sage and foxtail lily seen here going to seed were already established here.

Because of the cost-savings of using very small divisions of fast-growing plants, the total installation costs included less than $200 of raw materials and new plants. Although existing plants to propagate aren’t often available, the small starts can be seen as the equivalent of using very small plants or plugs from a nursery. Summer 2020.

Fast-growing, tall/large meadow garden plants include:

  • Large ornamental bunchgrasses such as maiden hair grass (Miscanthus), indiangrass (Sorghastrum nutans), big bluestem (Andropogon gerardii), switchgrass (panicum), feather reed grass (Calamagrostis varieties), giant sacaton (Sporobolus wrightii), pink hair grass (Muhlenbergia capillaris) and ravennagrass (Saccharum ravennae). Some of these get very large so be sure to read the description.
  • Fernleaf yarrow (Achillea filipendulina)
  • Russian sage (Perovskia atriplicifolia)
  • Maximillian’s sunflower (Helianthus maximilanii)
  • Artemisia ‘Powis Castle’ (Artemisia hybrid)
  • Showy milkweed (Asclepias speciosa)
  • Goldenrod (Solidago)
  • Joe Pye weed (Eutrochium purpureum)
  • False indigo (Baptisia australis)

Additionally, a meadow garden needs variations in height with many shorter species as well. Often, the best medium-sized perennials are those that will spread, multiply and/or reseed.

Second-order plants to quickly fill a meadow garden:

  • Medium-sized ornamental grasses including fountaingrass (Pennesitum), little bluestem (Schizachyrium scoparium), blue grama grass ‘Blonde Ambition’ (Bouteloua gracillis), as well as spreading or running grasses such as blue lyme grass (Leymus arenarius) or ribbon grass (Phelarus arundinacea). Be cautious with the spreading grasses, some may overtake non-aggressive plants.
  • Prairie sage (Artemesia ludoviciana)
  • Yarrow (Achillea milefolium)
  • Meadow sage (Salvia nemorosa)
  • Rocky mountain penstemon (Penstemon strictus)
  • Lupines (various species, Lupinus)
  • Lamb’s ear (Stachy’s byzantium)
  • Butterfly weed (Asclepias tuberosa)
  • Jupiter’s beard (Ceranthus ruber)
  • Bearded iris (Iris germanica)
  • Siberian iris (Iris siberica)
  • Black-eyed Susan (Rudbekia hirta)
  • Purple coneflower (Ecinacea sp)
  • Globe thistle (Echinops rito)

Another way to quickly conquer space in a new meadow garden is by scattering seed around the perennial starts. Some commercialized “wildflower garden” seed mixes contain a wide range of annuals and perennials to fill a garden. I tend to avoid blends because I like to be more intentional around plant placement and develop drifts of the same species.

My favorite starter seed types to spread in the garden:

  • Blue grama grass (Boudeloua gracilis)
  • California poppy (Eschscholzia californica)
  • Sunflower (Helianthus annum) — the regular wild kind. I often use plain bird seed! It’s cheap in bulk, and the plants are drought-tolerant and multi-flowered, grow quickly in any soil and attract birds.
  • Blanket flower (Gallardia) — this is a short-lived perennial but often blooms the first year
  • Penstemon species — if the garden is dry or non-mulched, they should have a good establishment rate. In thick mulch they may not.
  • Prairie coneflower (Ratibida pinnata)

Finally, when the core garden plants are in place, you can add dimension and detail to the garden by introducing a few non-spreading accent plants that hold their own against their aggressive neighbors. Some of them are tall spires that break through the surrounding plants. Some start growing early in the spring to avoid competition. The rest line the garden’s edges and paths, where bright sun reaches lower levels.

Some of the showier, non-spreading meadow garden companions include:

  • Blue oat grass (Helictotrichon sempervirens)
  • Various non-creeping Sedums, although some groundcover sedums can fill gaps as well
  • Blue fescue (Festuca glauca)
  • Daylillies (Hemerocalis)
  • Foxtail lily (Eremurus)
  • Prairie blazing star (Liatris spicata)
  • Fall-planted bulbs, particularly Alliums: Allium ‘Purple Sensation’ (Allium aflateunense), Allium ‘Purple Rain,’ ‘Drumstick’ Allium (Allium sphaerocephalon), species tulips, particularly Tulipa clusiana and Tulipa bakeri.
By late sumner of the first year, you can already see many of the new plants filling in. The Russian sage, which has grown large in this photo, was part of the previous garden in this spot so it is much larger than the new plants. Summer 2020.

Maintaining the garden


Few garden plans are so perfect from the get-go that you don’t need any tweaks. You may find a species doesn’t fill in the way you’d like, or that you’d like to expand the color palette. Plan on adding a few more plants here and there as time goes by. You might even choose to toss in a few handfulls of seed. A caution: when over-seeding a garden, I favor adding single species in a section at a time. Although this garden style allows plants to mingle, too many different species growing in the same patch can cause detract from the desirable contrasts found in larger drifts.

After about a year since it was planted, you can see that the meadow garden has already filled in well and is putting on a colorful display. June 2021.

Ultimately, meadow gardens can be very low-maintenance. Weeds have a hard time finding an opening among densely-packed, tough established perennials and grasses. Dead flowers set seed that feeds birds and adds winter interest. Insects and animals move in, enjoying the shelter and food source and keeping each other in check. Pest insects are unlikely to become a nuisance when plant varieties are very diverse and predatory insects are always present. All you have to do is sit back and watch, or do as much or as little as you’d like.

Another view of the Westminster, Colorado garden in early summer 2021.

When to trim back

One popular approach to meadow gardening is to cut dead stems down in late winter, just before green shoots emerge. I leave the downed material in place as mulch. Spring rain and snow will quickly soften and compress it as it is covered by new green growth. Earthworms tug the dead leaves into the soil so they soften and partially decay, at which point they become the worms’ food. You can choose to spot-trim things that bother you or become overgrown, and gently nudge your plants with selective thinning. When a competing plant is ready to grow into the void, the plant you are trying to reduce will stay in check long term. But like always in a meadow garden this work always optional.

Whatever you choose, the basic perspective I employ in meadow gardening is that it’s always much less work than spraying, mowing and aerating a lawn, or reseeding dead patches and managing insect pests. And the meadow garden, with vibrant colors and textures and a host of animal guests, is a lot more fun to watch and explore as time goes on.

A primer on the cactus family, and growing mountain ball cactus, Pediocactus simpsonii, from seed

Cacti make up one of the most diverse and rapidly-evolving plant families in the world, native exclusively to the Americas.

First appearing about 35 million years ago (fairly recent for such a large group of plants), the first cacti were thorny tropical shrubs with woody stems and lush leaves. They’re hardly recognizable as cacti, but you can still see these ancestral plants in the genus Pereskia.

A leafy cacti from the genus Pereskia growing in the Kona Airport gardens on the Big Island of Hawaii, hardly recognizable as a cactus except for the clustered thorns on the stem emerging from structures called areoles that are unique to cacti.

Nature’s high-tech survivors

Cacti employ an advanced type of photosynthesis, in which pores only open at night in cool temperatures to absorb carbon dioxide. They bind carbon as malic acid, a very weak acid found in many life forms, in special cell organs called vacuoles. They close their pores at dawn, before the air heats up, then draw four-carbon malic acid molecules into chloroplasts during the day to use it in photosynthesis without losing water to evaporation. Only a few plant families in the world can do this, allowing them to make glucose with minimal water loss. The same process arose independently in bromeliads, orchids and a few other groups.

Many of these carbon-storing plants are succulent, since thick fleshy tissues create more space to store carbon. That trait provided an added benefit of reducing the mass-to-surface area ratio which further limits evaporation, and storing lots of water, for a second level of drought-resilience.

With these evolutionary tools in tow, cacti quickly colonized areas other plants couldn’t. They lost their leaves, climbed into trees in the rainforest where they could grow without soil, advanced up dry rocky cliffsides and mountains, and eventually developed the familiar spherical, paddle and columnar shapes widely recognized as cacti. They then spread into extremely hot and dry areas west of the Andes and across what is now Mexico and the American Southwest.

The most famous cactus, the saguaro, grows in the Sonoran desert where the region’s average 10-15 inches of precipitation per year come in relatively short downpours followed by many dry months. Additionally, rainfall can vary widely year to year—some years receive up to 20 inches of rain and others as little as two. To grow large, plants need to be able to quickly absorb water when it is available and draw from reserves over many months, which cacti do by swelling and gradually contracting.
An epiphitic cactus clings to tree bark in a tropical rainforest. It is able to grow without soil thanks in part to its water-saving biology.

The cactus family’s evolutionary diversification has been remarkably fast, with new cacti species appearing every few thousand years to give us some 2,000 documented kinds today. But because of the tropical origin—to the chagrin of northern gardeners—most cacti are still unable to survive cold winters.

In the cactus family, the genus Opuntia has the most species that can survive sub-freezing temperatures.

The genus Opuntia, or prickly pears, are one exception, a large genus containing a lineage that rose with the Rocky Mountains and eventually spread to the plains, eastern U.S. and Canada. Another is the genus Pediocactus.

The Mountain Ball Cactus of the Mountain West

Pediocactus simpsonii, or mountain ball cactus, is one of the hardiest cacti outside Opuntia. Native to the high plains, Rocky Mountains and sagebrush steppe valleys of the western U.S. up into Idaho, Oregon and Montana, the cactus clings to shallow gritty or powdery soils among thirsty pine tree roots and nestled under tufts of bunchgrass or between rocks.

This hardy cactus can reach 11,500 feet in altitude and survive temperatures of 35 degrees below zero (-35°F). It grows to around 3 inches tall by 3 inches wide as single plants or small clusters. Unlike some other globular cacti, it is tolerant of part shade, and in hot dry weather it partially dehydrates and shrinks downward to hide from the sun or herbivores. The small globes plump up with snowmelt or rains in early spring, when they bloom and set fruit, spread by birds.

For a long time I thought these cacti were rare, though perhaps I wasn’t looking close. During the spring of 2021, when most of the Western U.S. was gripped in drought, the grass and wildflowers grew unusually thin, exposing the little cacti in their multitudes.

On a family member’s undeveloped 5-acre property in the foothills west of Berthoud, CO, I came across dozens of them around the bases of planted pinyon pines where they seemed to thrive despite the competition of thirsty tree roots. With permission from the owner (my grandma, who until then had no idea the cacti were there) I picked a few fruits, smashed and strained them and collected the seeds. There were dozens in each crambeery-sized fruit, each one a very hard black sphere about the size of a poppy seed.

Weeks later on a camping trip on BLM land near Radium Hot Springs, a dry forest of pinyon, juniper and sagebrush between higher Rocky Mountain ranges, I found literally thousands of mountain ball cacti—a cluster every few feet among the sagebrush and around the drip lines of pinyon trees. At around 8,000 feet, they were early in the growing season and just starting to bloom.

A pair of Pediocactus simpsonii cacti in a sagebrush meadow in a pinyon-juniper forest close to Radium Hot Springs near Kremling, Colorado.

Growing Pediocactus from seed

Pediocactus seeds are reputedly difficult to sprout. Like many plants that thrive in harsh climates, they have internal barriers that ensure their progeny hide away in the soil for years or decades until an opportunity arises. This is commonly referred to as seed dormancy which prevents seeds from sprouting even when they’re moist.

Triggers could include mild spring weather after freezing, a wildfire that clears the ground of competitors, a flash flood that shifts the soil, a dry spell that leaves gaps in the grassland or just the advance of time. Thar way, droughts or events that injure the established plants or leave them unable to bloom for decades won’t wipe out the population as a whole.

The best way to grow the seed, according to most sources, is to plant them in containers outside in a suitable climate and simply wait for the best conditions to occur naturally. That could take six months to a year and even then may only get you a moderate germination rate. With a few contradicting, anecdotal accounts about the best way to grow the seed, I thought I’d subject my seed collection to a science experiment to improve the odds and come to a more objective answer.

Testing various methods of germinating Pediocactus seeds

To test my seeds, I the collection into plastic bags with paper towels and introduced them to a variety of conditions. One bag was not given any treatment, two were scoured with fine sandpaper, one sanded batch and one unsanded batch was moistened and frozen and thawed several times over about two weeks, and one was subjected to the same freeze-thaw treatment dry. Another was wetted with hydrogen peroxide and left at room temperature.

After the treatment, the seeds were planted in a seed tray with mixed sand (50 percent), potting media (25 percent) and vermiculite (25 percent), packed down and covered with an additional 1/8 inch of sand and potting media. The seeds then went into a clear plastic bin and set outdoors for light and warmth to germinate.

At about three weeks in, I’ve spotted my first seedling—a tiny green sphere no bigger than a grain of sand, in the hydrogen peroxide row. That surprised me! I was expecting the sanded+frozen+thawed seeds to emerge first if any did at all.

The first seedling, in the hydrogen peroxide treated (center) row, is barely visible in the lowest cell of this image.

I’ll keep updating to follow the progress of this batch.

What is a crevice garden? An intro to a fun and attractive trend in xeriscape

A crevice garden is a style of garden arranging rocks in layers sticking vertically out of the ground. Originating in the Czech Republic, the crevice gardening style mimics natural rock features and plants growing from cliffs and crags. This charming practice is increasingly popular in the United States, particularly Colorado.

An alpine crevice garden at the Denver Botanic Gardens.

Thousands of species of plants around the world are adapted to grow in small spaces between rocks. In some cases they are so accustomed to this life that the plants—sometimes classified as lithophytes—are difficult to cultivate in typical garden soil. Crevice gardens employ plants with long, wiry, penetrating roots that find water supplies deep in the rocks, but loathe being excessively wet at the base of the stem, and don’t fare well with competition from larger plants.

Additionally, many plants that grow fine in garden soil can adapt to rock crevices—plants like huchera, penstemon, creeping phlox, candytuft, lupines, ajuga, dianthus and more. In nature, cliffside plants even include some trees, which will attain a more compact, dwarf form under the confining conditions. When native pines grow in tight confines they develop natural bonsai appearance and can live for decades or centuries without getting more than a few feet tall.

In a newly-planted crevice garden in my garden, sedums, sempervivums, Pediocactus, Ajuga reptans and Liatris punctata coexist happily despite having varying water needs in a standard garden.

Crevice gardens counterintuitively support plants that need dry conditions to thrive, as well as hosting plants that like moderate moisture, since the roots can reach deep into wetter spots within the rocks. They do this by allowing the root tips to stay wet while the crown stays dry. Plants in these spaces also benefit from not having to fight the aggressive root systems of nearby grass, shrubs and trees.

This is a great technique for growing small succulents and cacti that get lost in an expansive garden, which is helpful because many cold-hardy cacti and succulents are very small and are best viewed up close. Pediocactus, sempervivum (hens and chicks), dwarf prickly pears and small sedums thrive in the cracks. It’s also ideal for many other native Western species adapted to the dry southwest or high Rockies.

Finally, a crevice garden is a great way to garden in the city with a small space! With a few square feet you can plant dozens of small, attractive plants, each in its own spot, without any being overtaken by the others. It is remarkably weed-resistant, is virtually maintenance free, and combines the aesthetics of stone structure with the seasonal change and movement of live plants.

Growing your garden’s resilience to drought

A drought isn’t merely an absence of rain or snow. In fact, many ecosystems around the world—and gardens designed to mimic them—are adapted to thrive despite long gaps without precipitation. If a dry period is part of a region’s natural climate cycle and doesn’t threaten local farms or the native ecosystem, it won’t be called a drought. On the other hand, a rainy region that experiences a heatwave or a partial drop in precipitation that stresses plants can be in drought even if it continues to receive some moisture.

Plants survive regular dry periods through a variety of adaptations. They store water (cacti and succulents), reach deep long-term reserves in the soil (tap-rooted plants), or gain the ability to slip into dormancy and regrow leaves when rains return (grasses are particularly good at this). Beyond all that, plants will grow at the density and size that the climate and soil allows. A reliably-wet region will grow into dense forests, tall prairie or lush marshland. A dry or variable climate will have clumps of short bunchgrass or scrub surrounded by gaps of bare earth.

Any of these ecosystems can be healthy and well-balanced. A stable, old-growth desert or chaparral landscape can be captivating and beautiful. In a garden, we seek to replicate that equilibrium by planting the right kinds of plants at the right density to match the amount of water we plan to give it.

Plants in vs. wet landscapes
In most natural ecosystems on Earth, the limiting factor on the size and density of plants is water. Plants will naturally fill in to the level that the climate and soil moisture can support before reaching an equilibrium. Although deserts carry fewer or smaller plants than the redwood forest at right, they still form attractive, captivating landscapes and gardens when they are balanced and healthy.

Yet even if you garden with well-adapted native plants, or water frequently, droughts happen. Healthy plants grow and multiply, bigger plants take up more water, and at some point they start to deplete the soil moisture and reach their limit. Eventually, your garden will max out its resources and become susceptible to drought stress. This can happen even if you are still watering! Your goal, as a gardener, is to help your plants approach the level in which they max out the carrying capacity of the garden and soil as a gradual plateau, rather than growing overly lush until a summer heatwave drops it off a cliff.

In Denver this year, we’re definitely feeling that cliff. This is a semiarid climate with an average of 14 inches of precipitation per year. But it anything between 8 and 20 inches is fairly normal, and most gardens here are irrigated. In mid-August 2020, we’ve had 6 inches of precipitation so far this year (about a third below normal) and are experiencing successive 95+ degree days that increase evaporation from plants and soil. Even gardens designed to be “drought tolerant” require supplemental irrigation right now, and many are looking stressed despite the help.

In the last post I went over some of the signs that plants are being stressed by hot summer weather. But no one wants to be dumping excessive amounts of water on the garden to try to revive traumatized plants, only to see them wither again the next day. So here’s how you prevent that from happening in the first place.

Encouraging a resilient garden

Mulch

Arbor mulch—a grinded mixture of sticks, bark, leaf fragments and blocky chunks of trunks and branches—is the best mulch for cooling soil and reducing water loss. It’s the best mulch for perennial beds, superior to stone or bark. But any organic mulch, including grass clippings or straw (which I prefer in vegetable gardens), will help cool and insulate soil.

Pea gravel mulch is an option in desert-themed gardens. Gravel heats up in the sun and doesn’t retain soil moisture as well as organic media, so it should be used where plants are well-adapted to dry heat. Some gardeners will choose it because it’s easier for reseeding plants to germinate in a thin layer of gravel than wood chip mulch, and gravel is more visually harmonious with cacti and succulents. Additionally, there are rare cases where certain plants like cold-hardy agave and other xerophytes (drought-loving plants) are vulnerable to crown rot in woody mulch.

Group plants by similar water needs

A garden needs as much water as its thirstiest plant. That’s what determines how much you need to water the garden to keep that plant alive. Spot-watering with a drip system can help account for some variability, but water spreads horizontally through soil, so you end up watering a larger area than one plant needs. The most efficient strategy is to section of larger plots of 10 by 10 feet or more according to the plants’ water needs.

Water deeply and infrequently

The concept of watering deeply and infrequently is confusing, or even counter-intuitive sometimes. Why would watering a lot, all at once, save water? Or why letting the ground dry out sometimes help plants stay hydrated? The answer to these questions will reveal a lot about the way plants grow.

The concept is basically this: plants’ roots will penetrate wherever the soil contains enough water and oxygen. Often, in gardens irrigated in short bursts every one or two days, that’s the top four inches of soil. Watering deeply—keeping the irrigation on for a long time so that it can penetrate more than a foot deep—makes sure that roots find an abundant water supply if they keep growing downward.

At the same time, watering infrequently serves three purposes: it allows the upper levels of soil to dry out, which limits surface root development and causes plants to direct their energy to the deeper roots; it allows soil pores to drain so oxygen can reach the lower layers of soil and enable deep root growth; and it conditions plants to toughen their tissues and moderate their growth so that they won’t be traumatized by intense summer heat.

A deep-rooted plant is more resilient to drought because there is a bigger, longer-lasting water supply in the deeper layers of soil. Deep soil is also safe from temperature swings, particularly heat, that can injure roots.

But the strategy takes consistency. It’s not enough to begin a deep watering regime in August when the heat wave is at its peak; if deep roots aren’t already there, you’ll be stuck watering daily to keep your plants alive.

Summary

  • Water is usually the biggest factor in how big and lush plants can grow on a site. When vegetation grows dense enough to use most of the available water, new growth will slow and stabilize.
  • Drought happens when soil moisture drops below normal, meaning there is now more vegetation than the soil can support. Plants will begin to show signs of stress. Gardens may become less attractive and more vulnerable to pests and disease.
  • Gardeners can limit drought stress by recognizing the amount of natural precipitation they get and the amount of irrigation they plan to provide in a specific spot, and planting accordingly.
  • Arbor mulch—wood chip mulch that comes from the disposal of whole trees and branches—has been shown to be better at preserving soil moisture than gravel.
  • A layer of straw or grass clippings can help preserve soil moisture and are better suited for vegetable gardens, where the soil is disturbed more often.
  • Group plants by water needs to make them easier to care for, and plant at a density that the site can support.
  • To encourage deep, healthy root systems, water deeply (long enough for water to soak deep into the soil) and wait a longer time before watering again, rather than applying small amounts of water on a daily basis.

Dealing with a summer-stressed garden

It’s hot! It’s barely mid July and we’ve already had some 100-degree days in the Denver area. The hottest time of year here is the last week of July and first week of August, so we’ll be struggling with these temperatures for some time. Some parts of the world are, of course, even hotter. Heat stress forces plants against the upper limit of their adaptations, and they may require intervention.

Signs of heat stress in plants

When the weather is hot, water evaporates much more quickly from leaves and from the soil. This is especially true in low humidity, which is even harder on plants. Plant tissues that lose too much moisture will wilt, scorch or die back.

Symptoms of heat stress overlap with symptoms of drought stress, but there are some differences. Because of the way heat peaks in the middle of the day, plants suffer from repeated assaults rather than a gradual scarcity of water.

Wilting

Wilting brugmansia
A brugmansia (angel’s trumpet) wilts in summer heat despite growing in moist soil.

The most immediate sign of heat stress in plants is wilting. When wilting is related to heat, it is notable that plants can wilt even when the soil is moist. The roots are still taking up water, but they can’t keep up with the rate of evaporation from foliage. The short-term solution is to wet the soil even more thoroughly to increase the absorption rate. You can further ease the strain on roots by mulching with wood chips, straw or leaves to cool the soil.

Leaf curl

A sunflower plant with permanently curled leaves from heat stress
This sunflower has curled leaves caused by damage from heat and drought. The deformation resembles damage from pesticides or certain infections, but in this case it began during a heat wave and didn’t affect nearby plants with a better water supply, suggesting hot weather was the culprit.

When dehydration occurs repeatedly or lasts for days, it can change the way young leaves develop. Cells on the margins of a developing leaf can’t get enough water to expand, while leaf centers develop normally. The uneven expansion forces leaves to crinkle or curl as they mature, and sometimes the deformation is permanent. This type of drought stress is especially common on fast-growing plants like sunflowers, tomatoes and peppers. (Note: viruses and other diseases can also show up as leaf curl. But if the problem began in abnormally hot weather and leaves are not discolored or dying, the likely cause is heat stress). The typical solution to leaf curl is to water plants more regularly.

Scorched leaf margins

Ohio buckeye tree with scorched leaves
Ohio buckeye trees are particularly prone to scorching during hot days, in which the margins of the leaves dry out and die. Although the damage is unsightly, this young tree will survive and produce healthy foliage in the spring.

Severe or repeated heat stress can scorch mature leaves by dehydrating and killing the outer edges of the leaves. Scorched leaves will not improve and the plant won’t look better until it grows new shoots. Mulch, deeper watering, and shade protection on atypically hot days will reduce the incidence of scorch. Resist the temptation to cut off damaged leaves; they don’t look good, but they still photosynthesize and that helps the plant to grow new, undamaged leaves. Meanwhile, the dead, scorched tissue helps to shade and protect lower foliage from further damage.

Sunscald

Unlike wilting and scorch, which are primarily caused by dehydration, sunscald appears when plant tissues are killed by bright sunlight. In the same way that ultraviolet light burns human skin, high-energy photons from the sun damage the chlorophyll and DNA in plant cells beyond the plant’s ability to repair them. Scalded tissue is permanently bleached white or tan. It’s especially common on plants that have recently been moved or brought home from the nursery. To prevent sunscald, move plants to a brighter setting by acclimating them gradually with shade, part shade, light shade and finally full sun. That allows leaves to produce compounds that absorb excess light or free radicals and will prevent sunscald from occurring.

Thermal burn

Leaves can burn on exceptionally hot days, especially when air temperatures are above 100 degrees. Foliage in direct sunlight, or plant tissues in contact with rocks, gravel or metal reach lethal temperatures. Plants are literally cooked to death: the absolute maximum temperature plant cells of any species can tolerate is 140 degrees, while 100-degree temps can kill cells if they go on for hours and the plant is not acclimated to heat. Thermal burn on leaves resembles frost damage. Stems through solar-heated rocks or gravel can be killed from the base, cutting the plant off from the roots. On extremely hot days—the kind of heatwave that happens once every few years—only shading can protect foliage and it’s impossible to prevent some damage. Water and mulch soil with organic material to prevent thermal burns on stems. To protect plants from further damage, leave burnt leaves in place to provide shade until the heat wave is passed.

Yellowing leaves

Brugmansia showing yellow leaves from heat stress
This Brugmansia (angel’s trumpet) is showing signs of moderate heat stress, triggering the plant to drop its older leaves. Yellowing is a natural part senescence (natural aging and death) and the fact that the plant has time to selectively drop certain leaves means that the stress is not as damaging, but is occurring repeatedly or over a long period of time. Although the stress is mild, it does mean that growth is being slowed significantly and the plant may even decrease the amount of live tissue so that the roots can better support the canopy.

It’s normal and healthy for plants to drop older leaves and grow new ones, and plants do so regularly. Older leaves don’t produce as much energy for the plant, and plants regularly recycle their canopies. When leaves turn yellow before they fall, they are dying in a controlled process that usually doesn’t harm the plant. However, during times of severe stress, yellowing can accelerate and many or most leaves may drop.

Spider mites

Crocosmia with spider mites
This crocosmia is infested with spider mites, causing the leaves to yellow. Tiny yellow or orange dots appear where the mites, which are barely visible to the naked eye, have sucked the fluid out of plant cells. Mites become much more active in hot weather.

Spider mites are barely visible to the naked eye, clinging to the sides or undersides of leaves and sucking the fluids out of plant cells. Mite damage appears as small, yellow dots that can expand and fuse together as the mites proliferate. Plants sensing this damage can drop all their leaves in an attempt to starve the mites out or make them go away. Mite-damaged perennials usually survive, but the damage can set them back for a season or severely stunt their growth. Smaller plants or annuals may die. Mites increase their activity in hot weather, and can overwhelm and kill plants in a severely drought-stressed garden. Water and humidity lower spider might activity. Insecticides, which kill beneficial predatory insects, can exacerbate the problem in outdoor gardens. The long-term solution is to water, mulch, and make sure gardens are full of heat-tolerant species planted at a density that the water supply can support.

Shock or early dormancy

Extreme heat stress can force a plant into dormancy as a last-ditch effort to survive. Trees will occasionally do this if they are transplanted in summer. Many cool-season grasses and lawns can go into and out of dormancy easily. Other plants will be left weakened or traumatized when they finally begin to regrow. Some plants are unable to go dormant at all, and just die. The solution is to water, and adapt your garden to drought so that it doesn’t happen again. If plants go dormant easily, it may be better to withhold water and let them stay dormant until cooler weather comes.

Suffering succulents! Understanding what succulents need to stay healthy

Succulents are trendy, beautiful, and the most ornamental category of plants with their wildly distinct colors and shapes. They give off the impression of foolproof plants that thrive on abuse and neglect with simple, one-size-fits-all needs.

A succulent container garden on a patio in San Francisco highlights the diverse colors and textures among succulent plants.
A succulent container garden on a patio in San Francisco highlights the diverse colors and textures among succulent plants.

That’s not quite the case.

Succulent enthusiasts’ common refrain is to “think of the desert;” give them lots of warmth and little water. Just don’t let them get cold, or freeze. That’s what their native habitats in the wild are like, right?

That’s not necessarily true either! I’ll explain.

What are succulents?

“Succulence” is really a very general term. It describes thick, fleshy organs that appear on different plants regardless of the plant family they come from. Succulent plants aren’t all related to each other: spiky-leafed succulents like aloe and agave are monocots, just as lilies or palm trees are monocots. Cacti, sedums and jade plants are dicots, the same as sunflowers or rhubarb. Succulence can describe succulent leaves (like an echiveria), succulent stems (like a barrel cactus), or succulent roots (like a phalaenopsis orchid).

Various types of succulent plants can include succulent leaves, succulent stems or succulent roots.
“Succulence” is a descriptive term for thick, fleshy plant organs that store water. Plants with succulent organs come from many plant families and are not closely related. The term can refer to succulent leaves (top row), succulent stems (bottom left) or succulent roots (bottom right).

Where do succulents come from?

Succulents are not all desert plants! Some are, which explains why they’ve adapted to store water through dry spells. A saguaro cactus, for example, is prepared to take advantage of a late-summer torrential thunderstorm that floods the Sonoran Desert with rain. The cactus will swell rapidly with water, and very slowly draw down those reserves through one or more years of drought.

In contrast, Sempervivums (commonly known as hens-and-chicks) are native to rocky alpine zones, thriving on exposed rock faces or gravely soils where the escape the competition of taller plants. Their succulent leaves allow them to survive where thin soil doesn’t hold much moisture, but they need periodic rain or snowmelt to recharge their small reserves. They continue photosynthesizing happily through winter and can tolerate deep freezes in cold climates. They’re also tolerant of part shade growing in the cracks of rocks, but can bake to death in very high heat.

Sempervivum (hens-and-chicks) come from rainy environments, using their water-storing leaves to survive in thin soil.

Other succulents thrive in mild coastal areas, where rain may be scarce but nightly fog or mist is a valuable source of moisture. A large number of popular succulents come from Mediterranean climates, such as South Africa, where winter rain offers a lush growing season, and then the plants hunker down in a semi-dormancy through summer’s dry heat. Finally, there are many tropical rainforest succulents—such as Epiphyllum cacti hybridized from cacti that root in the bark of rain-drenched trees. They enjoy frequent rain, but don’t do well with waterlogged soil.

Rhipsalis cacti are just one of many types of succulents that are adapted to humid, tropical rainforest conditions.

So you can see that these plants come from diverse conditions. With that in mind, when you bring home a new or unusual succulent it’s best to do some reading on that specific species to avoid the risk of failure. But there are still some general rules you can follow for a diverse collection of succulents.

General succulent needs

Fast-draining soil

Planting succulents in loose, fast-draining soil or potting media helps them oxygenate their roots and maintain a healthy root system. “Succulent potting mix” is high in sand, perlite, chunky organic material or small stones.

Drench-and-dry watering cycle

Succulents survive dry spells by storing water in their tissues. When you do water, you don’t need to be stingy. Give them enough water that they can completely fill their reserves and swell to full size. Saturate the soil until some water drains from the container into the tray; that could mean, in a one-gallon container of gritty soil, that the soil can hold a quart of water or more. (It’s OK to leave standing water in the tray for a short time to make sure the soil is absorbing water, but for most succulents, you’ll want to dump out any remaining water that is still in the tray after a few hours.) For a healthy, vigorous plant growing in warm temperatures, soil moisture can be used up quickly. But don’t water again until the soil’s surface is dry to the touch.

Give your succulents enough sun

It’s inevitable that you’ll occasionally mess up and give plants a little more water than they like, but a healthy plant that is receiving plenty of light can defend itself against rot. Indoors, that often means the plant needs to be directly in window, close to the glass, with at least some direct sun. When plants start to appear pale in the center or “stretch out” on long, soft stems, that means they’re becoming etiolated. Plants do this to try to climb over whatever is blocking the light, and it can indicate poor health. It can be hard to re-adapt a severely etiolated plant to full sun. It’s better to avoid the problem completely by keeping them in a very bright location.

Don’t overfertilize

Succulents typically grow slowly and therefore don’t need a lot of fertilizer. That’s especially true in the winter, or if the plant is indoors, where fertilizer can trigger lanky, weak growth.

Move your succulents carefully and sparingly

Succulents grow slowly and hang on to their leaves and branches for a long time. That means it’s harder for them to adjust to changing light levels, or turn their leaves to face light. They need more time to adapt to new conditions than other plants. Resist the urge to move them around or rotate them often—do so sparingly. If you move plants outdoors, it’s vital to harden them off in shaded areas before exposing them to full sun.

A sunburned
A Cotlydon orbiculata plant (“pig’s ear”) with sunburn from being moved into full sun too quickly.

Summary

  • Don’t assume that all succulents like to be very dry. Some come from more humid climates and prefer more water—you may need to identify the particular succulent species to know what it likes best.
  • In general, succulents resent standing water and will prefer a fast-draining soil mix. A container with drainage is a must.
  • Water succulents enough for the tissues to stay plump—wrinkly or withered leaves are a sign of drought stress. Each time you water, do so generously, then let the soil begin to dry before you water the plant again.
  • As houseplants, succulents generally need to be kept in brighter areas, close to windows, and especially ones that get direct sun.

Cloning from cuttings: simple plant propagation techniques for home gardeners

Most of us got our first trial at plant propagation by sticking a sprig of mint or philodendron vine in a glass of water. After a few weeks, we had roots! Then they were ready to be planted in soil.

Plants that root in water

There are a number of plants which can be propagated in this exceptionally easy way: coleus, dieffenbachias, begonias, brugmansias, tomato plants, bee balm, many types of salvia, dracenas, african violets and more. These plants resist rotting, absorb water directly into a freshly-cut surface, and may have latent root buds along the stem. Many come from the mint or nightshade families, or are tropical houseplants, selected from species that tolerate wetness and are adapted to rooting quickly to spread in their highly-competitive native habitats.

Cacti and succulents

On the other end of the spectrum are succulents, many of which would rot in water but carry enough moisture in their fleshy leaves or stems that they can root in soil without special care. Most sedums, aloes, aeoniums, jade plants or cacti will easily root after air-drying for a day or two and being inserted directly into soil. They can last a long time on stored water so the cuttings can live for weeks or months without roots. Some types of succulents will generate new plants from a single fallen leaf.

Everything else

The largest number of plants fall into a difficult middle category: they’re both vulnerable to rot in pure water and unable to store enough to live without their roots unless they have some sort of life support. Some species seal wounds quickly and won’t take in water through a cut stem in a vase. Others are adapted to dry climates and haven’t developed defenses against bacteria and fungi that live in water, or can’t transport oxygen to submerged tissues so they suffocate and die below the water line. To get these cuttings to root, you need to control their environment more carefully.

Industrial nurseries use elaborate systems for this: tight temperature controls, chemical formulas, sterilized equipment and sprayers that mist the plants every couple minutes to keep leaves consistently wet. They’ll even create new plants by tissue culture, an advanced propagation process starting with small clusters of cells added to a sterile petri dish. For the home gardener, this is too elaborate to be practical, so some of the most challenging plants are beyond our reach. But we can still propagate a long list of plants at a moderate skill level with a fairly simple setup.

A simple nursery setup for cuttings

I propagate most of my cuttings in a basic “greenhouse” made with clear plastic containers and plastic wrap. The clear container lets me see the young roots forming, and the plastic wrap will trap humidity to achieve a 95-100 percent humidity level that prevents cuttings from losing moisture. I fill it part way with a rooting media (potting media, sand, perlite or vermiculite). Most plants are OK with potting media but some of the plants that rot more easily need an inorganic substrate.

Artemisia ludoviciana cuttings, prepared from a single stem, cut into segments and prepared to be stuck into a rooting media.

There’s no easy rule to determine whether a plant is easy to propagate by cuttings or how to select the best part of the plant to use; plants are too diverse. I recommend looking up the species or variety to learn its propagation methods. Government databases, universities or botanical societies have straightforward online databases to search. You should find whether or not propagation from cuttings is possible, the best time of year to take them, whether the best tissue comes from the stem tip or the base of the stem, whether to select young or old stems, you’ll see how long the cuttings should be, whether the rooting media should be kept very moist or on the dry side, and other variables that will impact whether your cuttings succeed.

Taking the cuttings

Generally, if I’m lacking more detailed info about a species, I will take a full stem from the donor plant if that’s available without doing too much damage to it. It’s best to do this in the morning when the stems are hydrated after a cool night.

I’ll take the single stem and cut it lengthwise into several individual cuttings. That way, one cutting will be made of old basal stem, which is hormonally prepared to root in many species, one cutting will be a young stem tip, which in some species forms the most vigorous roots, and gradations between them. I make sure each segment has at least three nodes (the place where a stem connects to a leaf and new shoots can emerge), and with each segment I’ll remove the lowest leaf and keep the top two.

Inserting the cuttings in the rooting media

It can be tricky coming up with the right moisture level for rooting media, since different plants prefer different amounts of moisture. A good middle ground is to wet the media thoroughly and let it drain so it is saturated but not super-saturated.

I stick the cuttings so that the node corresponding to the lowest leaf is right on the surface of the rooting media. That places one node at the bottom of the cutting under the media, one internode is buried the media, and one node is partially covered. Two leaves are able to photosynthesize, but the top leaf is completely clear of moist rooting media in case the one resting on the media rots. The batch contains variety of tissue types and positions from which roots may grow.

Artemisia ludoviciana cuttings have been stuck in the rooting media, in this case vermiculite that has been wetted just enough that no water drips out when tipped on its side.

Rooting hormone powder or gel is optional. It certainly helps plants that are harder to root from cuttings, while fast-rooting plants produce a lot of the same hormone internally and won’t derive much benefit from what you add.

If the stem is rigid, you can stick the cutting directly into the media, but in most cases it helps to dig a hole with a pencil or toothpick, insert the cutting and pat down the media around it.

The Artemisia ludoviciana cuttings are wrapped in plastic wrap to keep the air inside humid. That way, the cuttings will not wilt despite lacking roots.

Maintaining the cuttings

After the cuttings are struck, I cover the container with plastic and poke small holes in it to enable a little bit of gas exchange. It can be placed on a windowsill that doesn’t get too much direct sun, or, more successfully, under bright white fluorescent lights.

A note on plant lights: Artificial light for plants doesn’t need to be special, but it has to produce light without too much heat, so do not use incandescent bulbs. The closer the light appears to natural sunlight, the better. Newer LED setups might combine red and blue light, which should work. Otherwise, plain white light is best. (DO NOT use blacklights or UV lights; plants don’t use ultraviolet light to photosynthesize. They use the same wavelenghts produced in the largest amount by the sun, which are also what your eyes use to see and it will appear white.)

Cuttings under artificial lights need to be on a timer: plants require a period of darkness every day to undergo a full metabolic cycle, but will root faster if there is more light than darkness. I use a 16-8 photoperiod, or 16 hours on, 8 hours off, unless I learn otherwise about a particular species.

Several sets of cuttings are wrapped up and placed under lights for rooting.

Moving to the next phase

Different plant species take varying lengths of time to root, so you’ll have to keep an eye on your cuttings by looking through the container. Sometimes I lift a cutting or two out to check, although I do this with caution because it can break small roots off or delay their growth. I usually move the plants to the next phase when the roots are a centimeter to an inch long.

After the cutting has formed small roots, it no longer needs the high-humidity environment under plastic wrap. It can be removed from the container transferred to soil to continue to develop there.

When a cutting is mature enough to transfer, it’s better to do it as soon as possible because the very high humidity environment under plastic wrap can leave plants vulnerable to forming mold or developing diseases. But the plant will be shocked and die if it is moved directly into dry air or hot sun, and needs some intermediate steps. Initially, you can transfer it into small pots in potting mix and left in the same environment with the same light cycle that it rooted in.

After the young plants form roots, they can be transferred into soil trays and returned to the same environment they were in before to continue to develop. After further growth, you can start moving them into brighter light or the more variable weather conditions outside.

From there, you can gradually harden your plants off. Watch closely for wilting or signs of severe drought stress such as leaves crisping up around the edges—if that happens, you’ll want to slow down the hardening-off process or cover the plants with a clear plastic bag to raise the humidity again.

If all goes well, root systems will quickly grow. When you see roots coming out from the bottom of the container, you can transfer the plants outdoors in shade on a mild day. Avoid hot sun! Over time, you can move the plants to a spot that gets early morning sun. You may want to pot them up into larger pots if you plan on leaving them in hot sun or overwintering them in containers. Otherwise, continue to introduce them to brighter light and eventually you’ll be able to plant them out in your garden!