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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.

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.

Do trees die of old age?

Everything in nature dies. Human beings can live close to a century, but few do, and no one has lived past 122. Dogs live on average 8 to 14 years. Some tortoises can live to be 200. In vertebrates, changes on the cellular level give animals an upper limit on lifespan. Cells can only divide so many times before they’re compromised, making older individuals much more frail and vulnerable than youthful individuals.

Plants are fundamentally different: the larger and more established plants are, the higher their survival odds become. Out of 1,000 seedlings, only one may live to become a tree. But once a specimen is mature, it can be extremely resilient. Many common trees have potential lifespans in the centuries, towering over rivals and growing stronger every year.

Despite this trajectory, it’s uncommon to see single-stemmed trees grow past a thousand years old. So what limits them?

This is one of those questions I love, because there are so many angles to understand it from.

A tree is a system of redundancies

Unlike vertebrates, plant cells do not age. A rooted cutting from an ancient tree is identical, on the cellular level, to a young plant.

In fact, even in old trees, the live cells—leaves, roots and cambium—are young. Old leaves fall off, and new leaves grow. Feeder roots—the thin, water-absorbing tips and branches of the robust structural roots—also die and regrow cyclically, the same way leaves do.

The xylem—the tubes that carry water and minerals up a tree—are already dead. These cells are the most important type of tissue in determining what makes a tree a tree. Xylem cells form cylinders and die as soon as they mature, becoming conduits for fluid. Because they’re dead, xylem tubes cannot self-repair. Within a few years they develop tears and air pockets that stop them from working, so new cells replace them. At their final stage, defunct xylem cells are the wood. They are the old growth rings on the inside of the tree, existing only to hold it up. Their replacements, new xylem tubes, continually form on the outside of the trunk’s circumference, as new growth rings.

Phloem cells—which transport hormones and sugars from the foliage to the roots—also die annually. Unlike xylem, they are soft and rubbery, not rigid. They are also still living when they do their work. When spent, they die and collapse to a fraction of their former size, and are ultimately pushed outward as bark.

Between the phloem and xylem is a thin ring of tissue—the secondary meristem—which originates all the structural cells. It is rapidly dividing, and cells there migrate in to become xylem and eventually wood, or outward to become phloem and eventually bark.

Thus, all tissues in a tree are constantly turning over. The tree is less like a body, and more of a system. A tree’s young living layer clings to the skeleton of its own dead xylem, like a modern city on ancient ruins, or the live surface of a coral reef. All the while, it is growing in size. With time the system progresses through a structural evolution that defines the stages in its life cycle.

One mechanism that gives trees more resilience is redundancy. Remove a branch, and the loss of its hormone signal will resonate through the rest of the tree. Other branches grow more vigorously to correct for the loss, restoring the ratio between roots and shoots. If a fire or animal damages the vascular cambium on one side of a tree trunk, the cambium on the other side of the tree will thicken to compensate. Meanwhile, cells around the edges of the wound will grow inward to hopefully seal it off.

The hormone signals plant parts send throughout the plant are the only way a twig has any awareness, so to speak, as to whether it is a lower branch on a big tree, or a seedling on a forest floor. Aside from environmental stimuli—light, water, temperature and nutrients—hormones control how different sections of a tree cooperate. For example, if you remove a twig and root it, the hormone signals it receives will change. It is now much closer to cytokinin-producing roots and not getting suppressing auxins from higher foliage. In response, it will begin growing more vigorously, taking on characteristics of a seedling.

Now with that background info out of the way I can get more directly to the question: if the tissue in the tree does not age, and it continuously resets its behavior based on ongoing hormonal cues, why don’t trees live forever?

The problem is the accumulation of defects, which, over time, can overwhelm repair processes. The tree eventually reaches a point where it is much more difficult to keep things working properly.

Plants do not have cellular aging, but old trees suffer structural defects

• First: bigger trees usually have a higher ratio of unproductive (non-photosynthesizing) tissue compared to productive tissue (foliage). A seedling has leaves, a short stem, and roots. In a big tree, the leaves and branches are much higher and farther from the root tips. That means there is a long span of vascular tissue that must be kept alive. Trees expand their canopy as they grow, but the ratio between the massive cambium covering the trunk and branches, and the finite horizontal surface area determining the canopy’s access to sunlight, increases. The vascular cambium needs to maintain complete coverage over the heartwood to protect it from decay. Over time, there’s less energy to invest in new growth, so bigger, older trees grow more slowly. They’re also less able to correct structural defects like wounds.

• As a tree grows, the redundant parts communicate using hormone signals to work as a cohesive whole. Genetics, size and environmental stressors determine the size and circumstances in which the tree transitions to its mature stage. Gradually it uses resources to produce flowers, fruit, and seeds, investing less in growth. Some long-lived species may also invest more in energy storage when they get big, slowing growth further.

• The most important limit on the lifespan of old trees is decay in the heartwood. Even healthy middle-aged trees have a few pockets of decay here and there, but the tree’s ability to add new wood each year keeps pace so the tree remains strong. In very old, very massive trees, it is more difficult to defend a vast surface area, especially when decay pockets begin to coalesce inside the tree.

(One of the limits on the size and age of douglas firs, a very big and long-lived tree, is the fact that virtually all wild trees live with a decay fungus called dyer’s polypore. The fungi grows slowy, and the trees can be ancient before they eventually fall, so it’s not harmful to the species as a whole. But theoretically, if the polypore were not there, doug firs might be able to outgrow redwoods).

• In natural settings, competition limits the lifespan of old trees. Size provides incredible advantages reaching light and absorbing water, but there’s a point when the benefits max out. A big tree doesn’t have the opportunity to shrink its tissues to a more manageable size in a drought or disaster without exposing its dead heartwood to the environment and decay. Any loss of canopy requires a corresponding loss of roots, allowing other plants and trees to colonize soil and challenge the old tree’s dominance. Ancient trees tend to develop large sections of exposed, decaying heartwood, which means big portions will eventually break off. This means they often lose their tops, resprouting foliage from lower down. That costs them the advantage of height, while they still face the burdens of high tissue mass and very large sections of exposed heartwood that lead to continued breakage. An ancient tree may go through multiple cycles of breakage or dieback and regrowth. Each time, it accumulates a greater burden of decay, since the cambium is less and less of an intact cylinder covering the structure. Eventually, trees cannot compete against their less burdened neighbors, and die off while middle-aged trees assume dominance.

One other thing, more speculative on my part: plants get viruses, and viruses are not curable in plants. Usually, the plant continues to live, but less vigorously. Many plant viruses are asymptomatic, and their only effect is a metabolic burden leading to more stress and less growth. Luckily, most plant viruses do not get passed on to seeds. So there may be a point when the viral burden is high enough that the old tree is struggling too much and a seedling tree would be much better off. However, there would have to be more study into old trees and the presence of asymptomatic viruses for me to decide whether this is a realistic factor.

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.

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.

Helpful Concepts In Gardening: How Plants Decide When To Recycle Leaves

Horticultural forums and garden guides are full of simple one-off questions about plants: Can I root this in plain water? Are these funny-looking bulges flower buds? How do I get rid of mites? And so forth.

Then there are bits of conceptual knowledge that answer a hundred questions at once. Understanding how plants work at a biological level gives us tools to make better judgment calls, and brush off so many of the myths and bad bits of advice.

One of those powerful basics is understanding how plants use their leaves. That is: the leaves, or green tissues in general, are there to photosynthesize, making energy from sunlight. They’re the only part of the plant that makes energy, feeding all the plant’s cells, including the foliage, stems, flowers, bulbs and roots.

Of course you already knew that. Who doesn’t? And yet, taking it to its logical conclusion inverts the way we gardeners casually talk about plants, as if energy exists in the soil and is extracted, “sent to” to the canopy. Practically all of us sometimes use the inverted language: “let’s cut off the lower branches so the tree’s energy will go into growing the top,” or “chop your spent perennials down so the energy goes into making new stems.”

This is, in reality, only superficially true. If a hungry animal, unexpected frost, hailstorm or gardener removes a severe proportion of a plant’s leaves, it’s true the plant will tap into stored energy to restore the balance between leaves and roots, which means growing new leaves. If growing conditions are favorable, regrowth begins swiftly; dormant buds can launch rapid cell division within days or even hours, and will eventually erupt with visible growth. Since all a plant’s cells are relying on stored energy the moment the leaves are lost, it’s best to quickly commit a portion of that energy to replacing them.

That is, plants don’t spring back vigorously after hard pruning because they so appreciate having been deadheaded or cropped. They do it as a survival strategy, because they need to get out of energy deficit as quickly as possible. The lush, pristine new growth, free of insect bites, spent flowers or wear and tear, can make it seem as though the plant has been happily rejuvenated. But don’t be deceived: replacing lost foliage is costly. It diverts energy that would have gone towards root growth, reproduction, or chemical defenses against disease. If a plant is defoliated repeatedly, it will be severely weakened, and can eventually run out of energy and die.

How plants prune themselves

Plants survive the tumult of nature by being ruthless. When leaves or branches are no longer helping the plant, they’re sacrificed. That means a leaf or branch that isn’t a net producer—consuming more energy than it currently makes with photosynthesis—dies.

There are many reasons leaves could stop being productive. Often, a lower leaf or branch is simply shaded by other higher parts of the tree, and dies through a process called “self pruning.” Older leaves that accumulate too much wear and tear, or oxidative damage due to age, eventually stop being useful and enter senesence, a natural process when they turn yellow, break down pigments to return mineral nutrients to the rest of the plant, and fall off. If the plant faces a drought, photosynthesis slows down, meaning that a lot of leaves and branches that were net producers are now in deficit. Those too will senesce and fall off, resulting in a thinner canopy with only productive leaves left.

This also means that moving, covering or turning a houseplant forces every leaf to go through a recalculation based on its orientation towards light. Some will no longer be in a good position, fall into deficit, and senesce, stimulating the plant to grow replacements. Understanding this process helps us recognize many useful things: that moving a plant too frequently could be stressful for it, that we can expect plants to accelerate leaf turnover when conditions change, and that a few yellow leaves here and there are no major cause for concern, especially if those leaves are older and lower down in the canopy.

It also gives us clues when it comes to helping our plants through trauma. When you plant or repot something and injure some roots, should you cut off some leaves to counterbalance the loss of roots? Understanding how the plant would respond to foliage loss—by pausing root growth to prioritize foliar growth—suggests its better to pamper it with extra water for a while rather than to pare down the top. Or, if a frost or hailstorm leaves a garden in tatters, is it helpful to cut off the damaged leaves and stems? Well, the remaining foliage, unsightly as it may be, helps the plant resume growth without drawing down its reserves. If a tattered leaf is too damaged to be a net producer, we know the plant sacrifices that foliage to invest in new growth on its own, and we can assume that anything that stays green is therefore productive.

None of this weighs against good structural pruning of trees, which is intended to promote strong branches rather than stimulate fresh foliage. In fact, arborists protect the tree’s energy supply by limiting pruning to one fifth of of the canopy at a time. We can also still trim plants and leaves for aesthetic reasons—we should just know we’re doing so for our own purposes, not the plant’s, and use moderation. And if additional rounds of spring hail are possible, it might be smart to wait until the danger has passed to do a hard prune that will trigger the plant to dig deep into its energy stores and create a flush of vulnerable, lush green leaves.

As a whole, I think the knowledge helps us slow down and be a little more tolerant of how plants take care of themselves. Of course many of us garden because we find it therapeutic or fun to clip and train, and we like to think of plants as needing our constant care . There’s still a lot of room for experimentation, but in this case, the garden is better when we do it a little bit smarter and use a lighter touch.

Wealth for worms: what a gardener should understand about soil

Soil is one of the most important concerns for gardeners, so I want to take a moment to address a few basics. It’s the medium into which we add our plants, it’s where non-woody plants retreat when dormant, it’s where water is stored, nutrients are recycled and it is the home for countless bacteria, fungi, insects and other organisms that play an important role in the garden ecosystem that we usually don’t get to see.

Defining soil

For most of us, the question “what is soil?” seems too obvious to ask. Maybe we don’t have an encyclopedia definition in our heads, but we know dirt when we see it: it’s that workable, wetable brown stuff that covers the Earth’s surface naturally, that you find wherever you dig, that must be cleansed from clothes and scraped out from under our fingernails, that tracks into the house and needs to be swept. In the garden, it’s the stuff plants use to anchor their roots.

But this is a good opportunity to draw a line and explain something that turns out to be exceedingly important to us gardeners: what soil is not. Specifically, potting mix is not soil. That stuff is better described as a “potting media” or “soil replacement.”

Native soils

Soil in any natural ecosystem on Earth is a blend of decaying organic particles and living and dead things, water, dissolved gas and small open pores of air suspended between very small particles of rock—a lot of rock.

By dry weight, native soil is almost invariably going to be between 90 and 95 percent rock, in grains that range from small (sand) to very small (silt) to microscopic (clay). The proportion of particle sizes determines much of your soil’s character. Whether your native soil is fluffy, powdery, sandy, hard as porcelain, dark and moist, gritty and dry or easily waterlogged, it’s still around 90-95 percent rock. The remaining proportion of composted organic material makes the rest of the difference in soil’s potential water and nutrient retention capabilities and texture. (I say “potential” because another important aspect to soil is its structure, which is something I’ll return to later).

Being mostly rock, soil from the ground is heavy—between 75 and 125 pounds per cubic foot. And that is one way you know the mixture of blended materials you call “potting soil” is really not soil at all. Your potted plants would be really difficult to lift and move if they were in soil. Additionally, every time you water, the container’s drainage holes would leak muddy brown water containing microscopic clay particles and dark-staining dissolved substances. When it comes to larger containers, root systems planted in native soil would mostly be concentrated in top 8-12″ of the soil volume where oxygen is most available, or wrapped around the outer edge of the container and clustered around the drainage holes were additional pockets of highly-oxygenated soil are available. In other words, dense native soil in a container would not oxygenate evenly, causing root systems to form distorted structures and waste the space in the center of the container.

Potting blends

Potting mix manufacturers make potting blends out of non-decomposed and decay-resistant shredded plant material, such as peat moss, or most commonly, shredded bark and wood pulp that comes from the byproducts of logging operations. Light, fluffy types of rock such as pumice could be added in to help reduce compaction and slow the breakdown of organic components. More commonly, perlite or vermiculite serves that function. Because the the types of organic material used are mostly nutrient-poor and there are no mineral particles to supply minerals to plants, slow-release fertilizers or compost blends will be mixed in to provide them. This sort of mix resists compaction and is mostly air, so dry potting media can weigh as little as 8 pounds per cubic foot. The abundant air space also helps the roots penetrate deeply and use the entire volume of the container. Generally, plants in containers eventually need to be fertilized, while plants in real soil generally do not.

The fact that containerized plants are not growing in soil turns out to be important when it comes to planting. That’s because a plant transplanted from a nursery container into the ground exists with its root system confined to a plug of non-soil in a soil environment. Ideally, the first “watering in” that is always recommended after planting a will help some of the native soil dissolve and infiltrate the potting mix plug, getting the roots in contact with the denser particles that tend to be better at releasing nutrients and carrying water. But that’s not always the case, and the failure of roots to integrate into the native soil bed in time for the next drought is a major reason newly-planted plants die. It’s why I advocate breaking up the rootball as much as possible when you’re planting a new plant in the ground, and, in some cases, shaking off or flushing out the potting media as much as possible to get roots in contact with native soil.

Where the nutrients are

Most gardeners are well aware that organic material releases a burst of nutrients into the soil as it decays. Additionally, small organic particles in soil are useful for storing nutrients in a way that makes them available to plants, and the bacteria and fungi that live on these organic particles provide a host of benefits to plants.

(As a side note, this understanding gives us some insight into the popularized practice of fertilizing gardens with “compost tea.” That’s the practice of running water through compost and capturing its tea-colored extrudate to water a garden as a form of organic fertilizer. It’s true that compost tea contains some dissolved nutrients and free-floating microorganisms, but it doesn’t contain the bulk organic particles that hold them in place and provide the most benefit to soil biodiversity. Why go through the extra effort to separate dissolved nutrients from the substrate that puts them to work? As clever as the idea may seem, there’s no scientific support for the idea that supplying nutrients in tea form improves plant health compared to a top-dressing of compost on soil.)

But a lot of us take for granted the fact that the rock particles themselves contribute to nutrition for plants. Rocks naturally release trace amounts of nutrients, or bind excess nutrient molecules that can be re-released later. That’s a reason why volcanic regions, where soils are full of fine mineral ash have some of the most fertile soils on Earth.

Understanding soil types

As a gardener, it’s good to understand the soil type you’re working with. Above I mentioned the three main particle sizes—sand, silt and clay—which lend to different soil qualities. Most soil will be a mix of all three particle sizes in various concentrations.

Sandy soil, with large grains and pore spaces, drains and dries out quickly. It is beneficial in that it is less likely to become waterlogged, but is also more likely to dry out. Since larger particles have a smaller surface area, they don’t exchange nutrients easily, and can become nutritionally poor.

Clay soil is made of microscopic grains that fight tightly together. It holds large amounts of water and resists drying. Oxygen has a harder time penetrating clay soils deeply, so trees growing in clay will have shallower root systems that stretch out farther. Clay is particularly vulnerable to compaction and in urban areas it can be very degraded. However, clay, with its high surface area (more than 1,000 times that of an equal volume of sand) is excellent at storing and exchanging nutrients with plants.

Silty soils, as might be intuitive, combine the qualities of sand and clay.

Loam is an optimum mix of sand, silt and clay. Many farmers and gardeners consider it the best: it carries the benefits of sand and clay but avoids the drawbacks. It holds both oxygen and water, and stores and releases nutrients. Additionally, loam can be divided into sandy loam or clay loam based on the dominant particle size. A lot of gardeners seek to create a loamy soil for their garden, but…

You can’t change your soil type

The mass of soil in the ground is huge. Since each cubic foot of soil weighs close to 100 pounds, a small back yard of 40 by 40 feet has 160,000 pounds of soil in the top 12 inches alone. And, while most root system activity occurs in the top 8 to 12 inches of the ground, deep anchor roots and the roots of drought-tolerant plants and grasses can extend several feet!

So imagine you’re trying to change your soil type because your current soil is heavy clay, and you envision creating an ideal, loamy soil for your vegetable patch by adding sand. To tip the soil past the threshold where it really behaves differently, you’d have to add enough sand that that there aren’t enough clay particles to completely fill the gaps between grains of sand, providing empty space That means your soil has to be more than 50 percent sand, and to amend a 10-by-10 foot area you’d have to truck in 5,000 pounds of sand and till it thoroughly to a depth of 1 foot. That’s a lot of work, and over time, living organisms and water are going to spread that sand deeper into the soil and out into the surrounding areas so you’re going to have to add even more sand.

I think it makes a lot more sense to just work with your existing soil. In truth, even the heaviest of clays can become excellent soil with proper management. Plants can be selected to work with the existing pH. Generally, plants can weave their roots around rocks and adapt to different soil depths.

Summary

Potting mix is a lightweight replacement for natural soil that is made of shredded plant material and added fillers and nutrients. It weighs about a tenth as much as natural soil, lets oxygen in more easily, and is ideal for plants in containers.

Natural soil is 90-95 percent small to microscopic rock particles, with the rest being composed of organic material. It weighs 70 to 100 pounds per cubic foot.

Soil is composed of sand (large particles), silt (medium particles) and clay (small particles). Most soil has a mix of all three, but one or two types may dominate. The balance between particle sizes affects the soil’s characteristics—for example, sandy soil dries fast and encourages deeper roots, whereas clay soil stores more water and nutrients, but is more prone to compaction. A well-balanced soil is called loam.

Organic material helps water and oxygen move through soil, provides food for beneficial microorganisms, and stores nutrients. But microscopic rock particles in soil also supply nutrients to plants, and gives soil weight to help stabilize trees and shrubs. Ideal soil has a balance of about 90 percent mineral particles to 10 percent organic material, which is close to the natural ratio.

Adding compost to soil will temporarily increase the soil’s organic component, but it will gradually break down until the soil reaches equilibrium.

Soil has so much mass that it is very difficult to add enough material to change the composition of a garden. For example, a 10 by 10 foot garden would require 5,000 pounds of sand to change the soil type from clay to loam. It’s easier for gardeners to add mulch to optimize soil and choose plants wisely to work with the existing soil type.