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.
If there were a scientific study on houseplant survival—a big ask since no one makes any money when houseplants survive—I’d guess the biggest killer is the way they’re watered.
Well, that, and being tossed in the trash.
Everyone understands that plants need water, and that “overwatering” is a danger as well. But that leaves a wide range of judgment calls about how much is right, from submerging plants in an aquarium and leaving them parched.
Not only do plants’ water needs vary by species, they also vary with temperature, light, the plant’s size and the rate of lush new growth. The soil’s ability to absorb and hold water, as well as the container volume, also affect how quickly plants dry out.
It’s next to impossible to prescribe a specific amount or frequency for watering plants without tracking an impossibly long list of variables. It’s more realistic to set plants up to tolerate a wider range of moisture levels, and learn how to see the signs a plant needs water.
For that, it’s good to understand the mechanism that injures plants when they’re too wet or dry.
Why indoor plants die from overwatering
In some of the wettest climates on Earth, the land gets up to ten meters of precipitation per year and springs to life with dense, lush misty forests covered in moss and vines. Overwatering is no concern to wild plants in the Pacific Northwest or tropical rainforests—they thrive in the constant drizzle of rain and mist. Yet if you remove those plants from the forest and put them in pots on a windowsill, they might be vulnerable to overwatering and rot. For all but the most drought-adapted species, the problem is simpler than you might think: it’s not that they die of over-hydration—they drown.
The most visible organisms on Earth are plants and animals, and there are big differences between the two kingdoms in terms of respiration. Animals’ bodies deliver oxygen to all their cells by circulating blood, which gets its oxygen from the lungs or gills. So enormous, metabolically-active creatures like hippos and whales can wallow in water constantly as long as they periodically poke their nostrils above the surface to breathe. That’s not true for plants, which lack an oxygen transport system in their sap, so they have to absorb oxygen directly into all their tissues from outside. Tree trunks, flowers, stems and leaves are covered in tiny openings—stomata—that exchange gasses with the outside air. The roots, which sometimes have stomata and sometimes absorb oxygen directly through their much thinner, more delicate outer skin, can only grow in soil that has holds oxygen. When roots reach lower layers of soil, too dense or damp or deep to exchange gasses with the air, they stop growing downward and instead spread horizontally through the fertile shallows.
Submerged roots can sometimes gather enough dissolved oxygen to survive in water, particularly if the roots are in clear water with few microbes. Hydroponic growing techniques use movement—the water is constantly circulating—to keep dissolved oxygen in the water. Even cuttings stuck in a jar can sometimes root, if the species is amenable to that (and as long as there are no rotting leaves or stems in the water, which is fatal for reasons that will soon be clear). But getting enough oxygen to pass through waterlogged soil is another matter, especially when there is decaying organic there.
Soil is full of bacteria and fungi, consuming bits of carbon and scavenging oxygen to fuel their metabolic needs. A healthy soil biome is an important component of the ecosystem, and when in balance it helps plants thrive. But bacteria and fungi are more tolerant of low-oxygen zones than plants’ roots are, and if soil oxygen levels drop low enough that roots start to die, those dead roots immediately become food for an additional flush of microbial life that causes the oxygen-starved zone to expand.
Although containers with no drainage can be interesting or attractive, there’s a risk that too much water will over-saturate the soil and drown the roots.
This is not usually an issue in wild soils, which naturally shed water downhill or let it drain down into the earth. In fact, rain carries dissolved oxygen into soil and pulls additional air down into the voids between soil particles as the water table drops. In a container, though, standing water crowds out voids for gas exchange and can block oxygen from reaching roots. After a few days without an oxygen supply, hypoxia can spread and kill off the entire root system. Then, the top of the plant will wither and wilt as if it weren’t being watered at all.
Drown-proofing indoor plants
The simplest way to protect containerized plants from drowning is to make sure the container has holes in the bottom to let excess water drain, pulling fresh air in behind it. A layer of gravel or sand at the bottom of a container doesn’t cut it; these only create stagnant voids rather than circulating air. To oxygenate the whole pot or container to prevent it from killing roots, there needs to be an opening for water to drain out at the lowest point, pulling fresh air all the way through. A shallow tray, only allowed to hold standing water for a day or two at a time, can catch excess water without creating dead zones, but a deep tray allowed to hold standing water for longer periods is risky. Coarse potting mix with perlite or vermiculite also helps oxygenate soil. A tropical houseplant will tolerate heavy watering in a container as long as excess water is allowed to drain and air seeps in.
A container with drainage holes and a shallow tray is all it takes to drastically reduce a houseplant’s risk of overwatering, allowing you to water more frequently and keep the soil moist for faster growth. This plant is a Senecio rowleyanus, or ‘string of pearls.’
Managing soil microbes
Plants from drier climates, such as cacti, aloes and other succulents, are more vulnerable to drowning. In addition to death from lack of oxygen, their roots face another threat: having evolved in dry soil, they don’t have the same level of natural resistance to the bacteria and fungi that grow in wet soil. If the level of water-loving bacteria and fungi in the soil builds up too high—even if the soil is still relatively oxygenated—pathogens can infect the roots and rot them out, or begin spreading up the stem and rotting the entire plant. This problem is even worse when arid-climate plants, used to the intense sun of the desert, are growing in the relatively dim indirect light of indoor spaces and become light-starved. With less energy to spend fending off disease, they’re more vulnerable to rotting when they’re waterlogged.
There’s no way to completely prevent disease organisms from reaching roots. Soil-borne fungi and bacteria are everywhere: their spores fill the air, settle on all surfaces, and attach themselves to stems and roots. Entire ecosystems of bacteria, slime molds, fungi, microscopic animals, viruses and amoebas live in every cubic inch of wild soil. There are far too many soil organisms to count—there are millions, and probably billions, of distinct varieties on Earth, each with its particular set of favorite conditions. Although the number of species is greatest in wilderness areas and mature garden soil, containerized plants still have a diverse array of microbes among their roots.
With so many species to deal with, and more coming in on every puff of air or grain of dust, we mostly trust nature to do its thing. By growing plants in conditions they’re naturally adapted to, we promote the best microbial environment for each type of plant. That means choosing the right substrate, and allowing soil to alternate between wet and dry to promote healthier roots.
Some types of plants call for coarse, sandy soil with more inorganic particles like perlite or bits of stone—with less food for decomposers, inorganic soils carry a lower microbial load (though they are far from sterile) and are better for plants that are at high risk for rot. Beyond that, alternate deep and thorough watering, which allows plant tissues to swell and store water, with letting the soil surface dry out. Microbes will multiply when the soil is wet, but the dry spells bring their populations back down before they become a threat. The wet-dry cycle replicates natural precipitation patterns, and plants are well-adapted to it, as long as you provide enough water with each cycle, and let the excess water drain out.
Underwatering
A brugmansia (angel’s trumpet) wilts in its container.
Compared to overwatering, underwatering is more straightforward. Living plant tissues are up to 90 percent water—thin cellulose cell membranes enclosing a soup of molecules that maintain life. While woody tissue is rigid on its own, leaves and stems need enough water to keep their cells pressurized and maintain their structure. If stored water drops below a crucial threshold, cells will lose pressure, wilt and die.
Not only do plants need water to stay alive—the same way animals need water or they will die of dehydration—plants use up water molecules when they photosynthesize. In direct figures, six water molecules combine with six carbon dioxide molecules to make a single molecule of glucose, which can be burned as energy, or attached in chains to make cellulose, lignin or other long-term structures as the plant grows. But under drought stress, plants close their stomata to limit evaporation and end up shutting down photosynthesis. Due to evaporative losses, it ultimately takes hundreds of water molecules to make a single molecule of sugar, and a chronically drought-stressed plant will stop growing.
Wilting, yellowing, dropping leaves or a lack of growth are all visual signs a plant might need more water. Plants should be watered enough to saturate the soil, until water starts to come out of the bottom of the container and fill the tray, and watered again when the soil is dry. Additionally, potting media that becomes bone dry can contract and lose its capacity to accept new water unless it is soaked for a few minutes or hours. If plants are being watered but still show signs of drought stress, check to see if the soil is still dry to the touch after being watered. If so, you may need to set it in a bowl or bucket for a few hours to let it swell, then remove it to let it drain.
Summary
Many houseplants can tolerate more water as long as they are in a container with drainage holes in the bottom that allow oxygen to penetrate the soil.
Putting sand or gravel in the bottom of a pot does not make up for a lack of drainage holes.
Cacti, succulents and other drought-tolerant plants should be planted in a course or sandy potting mix that dries faster and has less organic material to reduce the amount of decay microorganisms.
When you water, water plants generously—enough to saturate the soil until water pools in the tray.
After watering a plant, let the soil dry on the surface before you water it again. A wet-dry cycle is natural and healthy for plants.
If bone-dry potting media is letting water run though without soaking it up, it needs to be set in a deep bowl or bucket of water for a few hours until it begins holding water again, then allowed to drain.
One of my earliest memories of being excited about plants comes from the heirloom amaryllises my grandpa had packed on every windowsill in their house. He kept them outside on a table or bench each summer, bringing them inside before the weather got cold. They bloomed in scattered succession from November to March. The antique bulbs were inherited from his mother—a non-hybrid species variety with salmon, daylily-sized flowers on curved stems that pale in comparison to the treelike poles bearing clusters of dinner-plate blossoms you find for sale in department stores each year leading up to Christmas. The heirloom has its charm, though, and is hard to find now except in rare specialty shops at a high price.
Species variety Hippeastrum striatum
I was so excited about my grandpa’s amaryllises that he gave me one when I was early elementary school age and it was my first experience caring for an indoor plant. I eagerly propagated it into a small collection. In our embarrassment of riches, though, our family took the antique bulbs for granted. Some were tossed intentionally when they developed scale infestations or mealybugs, others were left out by accident past the first frost and transformed into sorrowful piles of soggy slime. Priority went to newer and more varied kinds of houseplants. I started collecting other types of hybrid amaryllises, cross-pollinating them and creating experimental hybrids with their seeds, and found myself short on space. I didn’t take any plants with me when I went off to college, and after my grandpa passed away in 2017, the last of his heirloom amaryllis bulbs froze to death in a cold snap that penetrated so deep it froze and killed the bulbs that had been stored in pots in their garage.
Sometimes, we don’t appreciate things until they’re almost gone. The amaryllis collection gradually dwindled down to a single specimen now siting on the floor next to the sliding glass door at my parents’ house, infected with a mosaic virus that stunts its growth. In healthier form the variety produces a constant supply of offsets, and my grandpa used to save them all and pot them up to form his vast collection of clones.
A note on names: amaryllis is a misnomer
The flowers we all know as amaryllis are technically not amaryllises at all, but hippeastrums. True amaryllises are temperamental plants native to of South Africa, a genus containing only two species, one fairly common—Amaryllis belladonna—and another extremely rare and yet-uncultivated offshoot only recently identified as a separate species. They are best suited for growing outdoors in dry-summer Mediterranean climates, such as coastal California, where they multiply rapidly and are so resilient that they’ve come to litter abandoned farmhouse plots and hug the neglected corners of parking lots. In contrast, these true amaryllises rot in hot humid climates and are very difficult to master indoors.
True amaryllis, Amaryllis beladonna, is a separate genus from which the popular houseplant has taken its common name. Amaryllis is native to South Africa, whereas the commercial Hippeastrums sold as amaryllis are native to South America.
True amaryllises are commonly referred to as naked ladies or surprise lilies. (And as if the naming confusion wasn’t complicated enough, those common names also apply to the separate but visually near-indistinguishable species Lycoris squamigera, which tolerates colder winters and the humid continental weather of the eastern U.S.) But the genus Hippeastrum, with hundreds of species that have been hybridized to countless colorful cultivars, is much more diverse and widely commercialized than Amaryllis. So it gets credit for stealing all the attention, and the common name.
Most people treat their amaryllis/hippeastrum as a throwaway seasonal decoration, like a poinsettia, enjoying it for a week or two of blooms and then tossing it out to buy a new one the following year. But some people are tempted to try to save their plants, and find them difficult. The plants are drought-tolerant and can hibernate for a long time so they’re close to invincible when it comes to keeping them alive in some form, but the problem is that amaryllis/hippeastrums prefer a lot more light than is available to most houseplants. Struggling to achieve reblooms, people have come up with an array of amaryllis care myths that only complicate the task of growing a healthy plant. In truth, amaryllis/hippeastrums are pretty simple and low-maintenance when put in the right spot.
Getting amaryllises to rebloom
Hippeastrum is a tropical genus native to equatorial parts of South America, and as such, it doesn’t experience much seasonal variation. It has the ability to go dormant in drought, but dormancy isn’t necessary for any purpose. The plant will rebloom in winter or spring on a windowsill without intentional forcing, although, if you have any particular concern about the timing, you can force a brief dormancy by withholding water in fall and re-introducing watering six weeks before you want the plant to bloom. Because dormancy takes time away from photosynthesis, and forces the bulb to sacrifice its existing foliage and invest energy into regrowing it later, I prefer not to force dormancy; flowers typically show up at any time January through May in the popular hybrids and that’s fine with me.
Size is everything
With every five to seven leaves, the amaryllis/hippeastrum plant produces an embryonic flower bud that hangs out inside the bulb until the right conditions occur for the inflorescence to develop. The increasing day length just after the winter solstice will set things in motion, although sometimes just moving the plant to a new spot, or other triggers—intentional or idiosyncratic—will set it off. The only thing that really matters in making flowering possible is growing a big, fat healthy bulb with the energy stores necessary to support the enormous blooms. Lacking a sufficient bulb size, the embryonic flowers will eventually self-abort.
Large, onion-shaped amaryllis bulbs are likely to be able to bloom when the dormant buds are triggered by changes in light. While the largest and possibly the second largest bulb in this pot will bloom, the multiple of offsets are too small and will need another year or two to grow.
Different cultivars of amaryllis/hippeastrum bear different sized bulbs, from the size of a shallot in dwarf varieties to a hefty grapefruit in the giant ones. Given the vast genetic range in size, an easy way to tell whether your amaryllis bulb is on track to rebloom is the bulb’s shape. If it’s fat and squat like an onion, that means it’s swelling rapidly, and is likely close to the maximum size and will have the strength to bloom. If it’s more slender like a leek or daffodil bulb, it has probably regressed to a juvenile phase and needs more time to build reserves.
The brightest light builds the biggest bulbs
And for this, the biggest challenge most indoor gardeners have with amaryllis bulbs is giving them enough light. They are at their best outdoor plants in warm climates, where they can naturalize in light shade. When grown at northern lattitudes, they perform best in a greenhouse, sunroom, or a south-facing window. Unless your home is uncommonly well-lit, your best bet is putting the plant directly on the windowsill or as close to it as possible since natural light diminishes dramatically even a couple feet from the glass. Or, you can place the plants outside in partially-shaded areas for summer (ideally in areas sheltered from too much wind or foot traffic). But beware: the straplike amaryllis leaves are prone to kinking or breaking, and when moved, the plant likes to let its existing foliage die off and produce new leaves, which uses precious energy. So you’re most likely to get a large, healthy bulb if you find an ideal spot and leave the plant there without moving it at all for at least 6 months at a time.
Water, soil and fertilizing amaryllis bulbs
Amaryllises are relatively forgiving when it comes to water. It’s good to water them thoroughly for a while and then let them dry out periodically, but avoid leaving them so dry that they begin to drop leaves. In bright summer light and in full leaf, one of the larger plants can use more than a quart of water per week, and in the lush vegetative period it’s OK to keep the soil continually moist. Occasionally, it’s good to let the soil surface become dry to the touch to avoid rot.
Most commercial indoor potting blends are OK for amaryllis, but if the soil is too dense or peaty I like to add perlite, or mix standard potting media with succulent mix. The container should be at least 3 times the diameter of a full-sized bulb, and have drainage holes. (Pots without drainage holes are doomed to failure, which is unfortunate when so many amaryllis grow kits come with pots with no drainage—perhaps the growers’ insurance that customers will have to come back for a new purchase next year?)
Amaryllis should be planted with two thirds of the bulb above the soil surface and should not be repotted often; their thick succulent roots are an expensive investment and disturbing them will force them to regrow, reducing the bulb’s size. They’re more likely to rebloom when rootbound and it is OK to combine bulbs in a container or allow bulbs to coexist with their own offsets. If you choose to force dormancy, it is possible to do so by withholding water or moving the plant into darkness without removing the bulb from its pot. If over the years the soil begins to lose volume or lose its ability to hold water, it’s possible to lift the plant and add soil without completely exposing the root system, although plants will be fine if repotting is limited to every 3-5 years.
Finally, amaryllises are a plant that enjoys a regular feeding, with dilute, well-balanced fertilizer, particularly in the fast-growing vegetative period in summer. That’s when you can really capitalize on the long days and bright light and grow a very large bulb. Avoid fertilizing them in the months leading up to blooming season, since nitrogen will stimulate long stems that are more prone to breaking. To avoid excessive accumulation of fertilizer salts, once or twice a year you can set the container in the sink and flush it thoroughly, letting water drain through the bottom of the pot, then try to return it to the same position it was growing in previously so it doesn’t behave as though it has been moved.
Bringing it home
Some amaryllis cultivars are hardier than others—apparent when identical windowsill conditions produce bulbs of vastly different sizes. In my experience, red or orange-flowered varieties tend to be more vigorous and light pink or white plants are more temperamental, often failing to rebloom when others would. But I don’t know if there’s anything substantial behind that pattern or if it’s just a coincidence. Regardless, it’s more than possible to keep a collection of amaryllis plants alive as houseplants indefinitely, for reliable repeat blooms, as long as you have the light and space. It seems like a shame to toss a perfectly healthy bulb that just finished blooming, and often department stores and clearances will put remaining bulbs on a deep clearance sale just after the season ends with Christmas. If you find yourself tempted, give it a try!
Summary
Amaryllises can be easy plants to grow, but need more light than most houseplants to grow large enough to bloom.
Keep amaryllises in a sunroom or south-facing window, as close to the glass as possible, to give them brighter light.
If you decide to put amaryllises outside for the summer, choose a sheltered, lightly-shaded spot. Be sure to bring them back in well before frost.
A dormancy period is not necessary to get amaryllises to rebloom. It may be easier to grow a larger plant if you don’t force them to go dormant, and avoid pruning off leaves while they are still green.
The natural blooming season for amaryllises indoors is late winter or early spring.
The main factor determining whether an amaryllis can bloom is the size of the bulb. A fat, onion-shaped bulb is a good sign that the plant has enough stored energy, while a thin, slender bulb is likely in a juvenile stage.
Amaryllises need a container with drainage holes in the bottom to thrive.
Try to move the plant as little as often so that the plant doesn’t drop its leaves.
Applying a dilute, well-balanced fertilizer in summer is helpful to promote lots of leafy growth that enlarges the bulb.
Water amaryllis bulbs deeply and thoroughly, then let the soil begin to dry out on the surface before watering again. They can survive long periods without water, but will do better with regular water.
After several posts on gardening science, it’s as good a time as any for some background on myself and how I came to starting this blog.
From 2016-2019, I lived in the San Francisco Bay Area. I worked as a copywriter and was experimenting in landscape design/installation with another designer who specializes in native California plants. (If you’re in the Bay Area and need a garden upgrade, I highly recommend checking out his website at evancooperdesign.com.) I’ve been an avid gardener my whole life, but Evan introduced me to the “meadow garden” style. He also gave me some useful principles in hardscaping and a deeper appreciation for grasses and plants native to the American West.
An Oakland, California garden designed and installed by Evan Cooper Design.
My background is in journalism, but I really enjoyed working with Evan. Beyond our easy working relationship, I loved working with my hands rather than computer screen. At the same time we were contributing to wildlife habitats and eco-friendly landscapes in an urban area. I was considering getting more involved in landscape work and education about horticulture.
That changed in May 2019. I broke my leg in a scooter accident, scrambling all those considerations. The injury was on the serious side—tibial plateau fractures usually cause major ligament and cartilage damage which in turn causes loss of mobility and triggers arthritis. More immediately, after a tibial plateau fracture, you probably won’t be walking for 3 months. I moved in with my parents in Westminster, Colorado to recover and regain the ability to walk, start rehab and embark on the long process of regaining the muscle strength and balance necessary to do rigorous physical work.
Just after I started walking again, an even bigger crisis struck my family. My mom was unexpectedly diagnosed with stage IV pancreatic cancer. My 61-year old mom had been a health nut her whole life, and the diagnosis was a shock, (although it’s no surprise to science that cancer often strikes at random).
Pancreatic adenocarcenoma usually brings an abysmal prognosis; fewer than 1 in 5 patients survive the first year and and only 3 percent of stage IV are alive in year 5. The only hope was in clinical trials, and we asked several oncologists for recommendations. At the University of Colorado Health Sciences Center, doctors found an experimental immunotherapy drug that looked promising. The logic behind the drug’s mechanism of action made sense to me, and as a participant of the trial my mom would continue to receive the standard chemotherapy alongside the experimental treatment. (For anyone struggling with a serious illness for which there are few or no adequate treatment options, I definitely suggest seeking out clinical studies. They offer not only the opportunity to try cutting-edge treatment, but also contribute to the body of knowledge that will help other people).
Early results were promising—after 6 weeks on the trial my mom’s tumors shrank significantly and many disappeared in imaging. We currently have no way of knowing if my mom’s progress is thanks to the experimental drug, an uncommonly strong response to the standard chemo, or some combination of both. At the very least, I can say that after 9 months on treatment my mom’s cancer is stable and smaller than it was when she was diagnosed. It may not be a “cure,” but we definitely expect my mom to outlive the typical survival time for pancreatic cancer.
At the same time, my mom is still immunocompromised and at high risk of serious illness during COVID-19. I’ve decided to stay home and social distance strictly to keep her safe and help look after her, and I’ve used the time to pick up a few part-time landscaping clients for income (so I can work outside and away from infectious people), and meanwhile do a full redesign of the my parents’ yard, including new trees, a woodland garden, vegetable boxes, a meadow garden, a desert garden, a native plant area, a cottage garden and a pond expansion to built a large aquatic garden and wetland area. That also gave me the time to start this blog!
Part of a newly-planted meadow-themed garden (foreground) and a desert-themed garden (behind) under construction.
So without further adeiu, here’s a video of what I’ve been building this summer.
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.
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.
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
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
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 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
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
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.
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.
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).
“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 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.
Growing a pineapple plant from a pineapple top is a fun and simple gardening project to do with kids, or an easy way to get a free, low-maintenance houseplant that actually looks pretty good in your home.
A pineapple top rooted a few months ago producing a new set of leaves on top.
For an industrious plant-enthusiast there is a litany of ways to turn grocery store produce or kitchen scraps into live plants—sprouting mango and avocado seeds, planting ginger root or replanting the base of your onions. They’ll all get you something, but out of all the possible scavenged garden projects, pineapple plants grown from pineapple tops make for the most decorative and tidy houseplants that look just as nice as a plant you buy from a department store or nursery. They have an attractive symmetrical shape and interesting spiky leaves, they don’t shed or make a mess and they are easy to keep alive on a windowsill, tolerating both overwatering and underwatering without much fuss.
You need:
A pineapple with a nice, green healthy top
A container or flower pot that is at least 6 inches wide (ideally 8 inches), and has drainage holes in the bottom
A tray to go under the container (unless it’s built into the pot itself)
Potting mix
A knife/cutting board
Scissors (optional)
A bright windowsill that gets direct sun—ideally one that faces south
Putting it together
First, cut the pineapple top off of the pineapple as close as you can get to the spot wher where the foliage meets the fruit. Inside the cluster of leaves there is a short, thick, somewhat fibrous stem that can be difficult to cut through, so if you’re with young kids you might want to leave that part to the adults. Make sure to remove all the fruit from your cutting; it just rots and it’s not where the roots emerge.
First: cut the pineapple top off of the fruit and cut off all residues of fruit.
Next, strip off some of the lower leaves to expose at least a half an inch of the bulky stem. At the base of each leaf you may see a tiny bud or node—those are small roots, ready to grow on contact with soil.
Pull off some of the lower leaves to expose at least half an inch of stem. New roots will emerge from the exposed area after the cutting is planted.
You can trim off dead portions of the leaves or leaf tips as desired to make the cutting more attractive; it doesn’t make a huge difference for the plant unless there was so much brown that it was shading out the green leaves, but it will be more enjoyable to grow if it looks healthy.
I like to use scissors to clean up dead sections of leaves at the tips. It’s not crucial, but makes for a more attractive plant.
Fill your container with potting soil up to about 1″ from the top. Dig a small hole in the center for the pineapple top.
Plant the cutting deep enough to cover all of the exposed stem and the bases of the lowest leaves.
Press the pineapple top into the soil so that the bare stem section is covered and so are the bases of the lowest remaining leaves. It’s OK if some soil gets into the crevices between the leaves. Compress the soil lightly around the plant.
A newly-planted pineapple cutting at the ideal depth.
Water the plant thoroughly, and place it directly onto your bright sunny windowsill. Pineapples need a lot of sun to root!
Be sure to place the plant close to a bright window to root. An established plant is more tolerant of receiving less light, but cuttings prefer some direct sun.
That’s it!
Caring for the plant
Keep your pineapple cutting’s soil moist by watering it regularly until a some water drains through and collects in the tray. That’s how you know the soil is saturated. It’s OK to leave a little standing water in the tray; it will help keep the soil moist as some of the water is drawn back in. Leaf tips may brown a bit as the plant struggles to grow roots, and you can trim them back with scissors. But the rooting process does not take very long and the plants aren’t temperamental.
Resist the temptation to lift the plant to check for roots; you could break the roots and force the plant to start over. The first sign that roots have formed is that the leaves will suddenly begin growing, especially the young ones in the center of the plant. They’ll soon stand tall above the others. You can safely cut back on water when that happens, and even add a dilute fertilizer every now and then for faster growth.
Collect different types of pineapple plants
Commercially-available pineapples are grown from 5 main classes with several varieties or cultivars in each class. All pineapples of a particular cultivar are clones (propagated by cuttings). Pineapples can’t self-pollinate, and since they are only grown among their own clones they won’t produce seeds since the plant treats pollen from a clone as being from itself.
The varieties of pineapples in grocery stores lead to slightly different-looking pineapple plants; some form a taller and spikier plant, some form a stouter plant, some plants have a glaucus coating that gives them a nice blue tint and some are deep green. Some have serrated or barbed leaves and some are smooth. You can tell the difference by looking at the pineapple top even before you buy it. The plants may have slightly different light and water needs, but for your purposes at home you can treat them pretty much the same.
Will your pineapple houseplant produce fruit?
A note: you probably won’t ever get a pineapple from an indoor plant; in tropical areas they can form fruit in a year, but indoors the plant will tend to reach a certain size and plateau. It can live indefinitely. However, you can eventually force your plant to fruit by covering it in a plastic bag with a ripe banana inside; the ethylene gas released by the banana will trigger a hormone reaction that forces a small pineapple to emerge in a few months. If it fruits, the main portion of the plant will stop growing and 2-4 shoots will emerge from the sides.
A note on starting your pineapple top in water
Don’t. I know people are used to starting cuttings in water and for many plants it’s a very easy way to propagate them, so it’s the default strategy when trying a new plant. You can find dozens of guides online that tell you to root your pineapple top in a dish with water, but there’s really no reason for it. Pineapples are not tolerant of being submerged; they rot easily in water, especially if there’s any fruit left attached to the stem. Meanwhile, they root with a high success rate in soil. So skip the unnecessary step!
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!
Bearded iris, Iris germanica, is one of the most easy and rewarding perennials you can grow. They can survive in xeric gardens with as little as 10 inches of rainfall a year, and will grow and bloom without care as long as they get plenty of sun. Multiplying perpetually, there is no limit on a bearded iris’ lifespan. They rarely if ever need fertilizer. They tolerate a wide range of soil types. In dry-summer climates they’re highly resistant to disease. They’re able to push back and hold their own against aggressive weeds and groundcovers, without ever becoming invasive themselves, since a clump of irises only creeps outward by about 3-4 inches per year.
Bearded iris are one of the most carefree and reliable garden perennials
They’re also rapid multipliers, which is both a blessing and a curse—a few new plants will become a cluster and a cluster will become a dense, thick mat of roots and leaves that eventually choke each other off and stop blooming. Like many clump-forming perennials, they’re prone to developing the “crowded doughnut” shape, with weak, depleted plants in the center of a cluster and relatively vigorous plants around the edge where there is still access to fresh soil and sun. To avoid this situation (or fix it), it’s best to dig and divide bearded iris every 3-4 years.
Timing
In truth, bearded iris is tough enough to be divided any time of year. But since it takes some time for roots to re-establish, the most often-recommended time to transplant is right after they bloom: in June for Northern Hemisphere gardens. The reason for that is not so much about the health of the plant (the least-stressful time to dig them, from the plant’s perspective, would probably be early fall) but so that the plants are completely recovered by the following spring when you want them to bloom.
It’s notable that June and July are very stressful months for plants to be transplanted, forcing them to re-establish roots in the midst of long, hot days when demands for water are at their peak. June is also the most productive time of year for photosynthesis, an opportunity missed if plants are dealing with their re-establishment phase when they’ll have fewer leaves. But this is the best time of year to do it if you want to maximize blooming the year after. Since bearded iris is such an easy and vigorous plant, one that can survive being unrooted for a long time and multiplies fast anyway, you can go ahead and dig it in summer without much harm. Why not? Spend the spring and fall transplanting seasons attending to your more temperamental plants.
How bearded iris grow
Irises grow from a rhizome, a form of modified stem that creeps along the ground just beneath the surface. Irises have a fat, fleshy rhizome for storing water and starch, which contributes to their durability. (Other rhizomatous species have simple, spindly rhizomes that help them spread rapidly but won’t enable them to live long outside soil). The top of the rhizome is usually exposed, revealing ribs where now-dead leaves used to be attached. The underside of the rhizome is covered with stringy, strong, fibrous roots that eventually die and slough off, leave small superficial holes in the rhizome.
A keen gardener who looks at the structure of different plants eventually comes the realization that all vascular land plants, from 350-foot-tall redwoods to dainty daffodils, are composed of the same three basic parts: leaves, stems and roots. Leaves and roots always attach to the stem, which, for most plants, is usually the only type of tissue that generates the other two types. Stems always grow new tissue from specialized cells at the tip, and produce new branches at nodes that lie dormant at the base of a leaf or leaf scar until it’s time to grow. Cells at the growing tip of a stem divide rapidly to form the basic structure, then stop dividing and go through an elongation phase to reach the full size, then harden and stop growing as they mature.
Whether plants grow from bulbs, tubers, crowns, corms or woody trunks, the dramatic differences in the way plants grow are simply a matter of the way these three main parts are arranged. In an onion, for example, the stem is a small mass in the bottom of the bulb called the basal plate, where the onions layer’s (which are modified leaves) are attached. The roots emerge from the bottom of the basal plate. Only this basal plate tissue can perpetuate the life of the onion; you can replant the base of an onion bulb to generate a new cluster of leaves, but you can’t plant leaves or chopped onions to grow new roots, nor can you generate onion plants from the spindly roots. In a potato, the entire edible tuber is made of stem tissue and each of the eyes is able to sprout new potato plants. If you look closely at a carrot, which is a tuberous root, the stem is a small area at the top of the root where a cluster of leaves emerges. Neither the root, nor the leaves, are viable on their own.
So the bearded iris’s rhizome is the plant’s main stem. The new cells are created inside a small, actively-growing region inside the fan, which is located at the young growing tip of the rhizome. New leaves are always emerging from the center of the fan, and old leaves are always sloughing off the outer edges, exposing new sections of rhizome. New roots emerge from just behind the spent leaves. Iris leaves are constantly being renewed, and roots are not long-lived either; they live about a year, and after they die, the older portion of the rhizome simply sits on top of the ground, anchored by the actively-growing regions at the tips where new roots are always forming.
Irises multiply in two phases. The most prolific is related to blooming. When an iris prepares itself to bloom, the actively-growing tip of the rhizome—in other words the growing tip of the plant’s stem—curves itself upwards and hoists itself into the air as a flower scape. There, the stem terminates, and the fan that it originated from will die.
Like so many other plants, pinching or terminating the growing tip of a stem forces it to branch. This is also true when a rhizome terminates in a flower scape. In fact, in early spring, before the flower buds even appear, the emergence of offsets that pop up just ahead of the main fan is a strong indication that this particular iris will bloom. Weak or shaded irises will produce 1 or 2 offsets per flower scape. Moderately-vigorous plants will produce 2 to 3 offsets, and highly vigorous plants will produce 4-5 new offsets to replace the portion that bloomed. That gives you a sense of how quickly irises multiply.
The second source of new offsets on a bearded iris comes from older nodes in the aging portion of the rhizome. These auxiliary shoots are usually small and will require multiple growing seasons to reach blooming size. Any old chunk of iris rhizome, whether it has leaves or not, will produce one or two of these types of offsets if it is separated from the rest of the plant. If you want rapid propagation of your irises there’s no reason you can’t keep every bit of living rhizome to create lots of new plants, but many gardeners will discard older portions of the rhizome when they divide their iris since the offsets from old portions take 2 years to bloom.
Digging and dividing
It’s fairly easy to dig, lift or yank bearded irises out of the ground. There’s not a lot you can do that harms the plant much, even if you lose some of the leaves in the process. When the cluster is out, you can shake or hose off the dirt and separate the cluster into individual plants.
Rhizomes will initially be connected together into large branching structures, tracing back to the original parent portion, which may or may not still be living tissue. To divide iris, you’ll need to break the branches apart into manageable bits. Some guides suggest using a sharp, clean knife but tearing is also fine. The exact point of breakage is not that important; separate the offsets into 2-6 inch sections each containing 1-3 fans. Try to maintain at least two inches of rhizome and at least one highly-vigorous fan on each segment, since it leaves you more likely to get blooms next year. But even smaller sections will grow stronger and produce blooms in the second year.
These rhizomes are still connected because they grew from the same original plants. The red lines are reasonable places to cut or break off portions for re-planting. If iris are divided and replanted in early summer, these divisions would be able to bloom next spring.
You’ll be left with a lot of nice-looking healthy green vegetative fans connected to rhizome, and a lot of leafless chunks of older rhizome or rhizomes with only small, weak vegetative shoots. You can feel free to plant these other chunks in a separate part of your garden to propagate more iris, or mix them in with the cluster you intend to keep, or throw them out. They will bloom in 2 years if grown in good conditions. They’ll also root in your compost pile.
Dividing iris will produce a lot of older portions of still-living rhizome. Some gardeners will discard them, but if you plant them they’ll produce shoots that bloom in 2 years.
Should you trim the leaves off of bearded iris?
Some gardeners consider it good practice to trim the leaves back when transplanting iris. There are good reasons for it, but they might not apply to every circumstance. First of all, if the plants are left out of the ground for a while to be shipped or stored, the leaves will dry up and die back. Irises never go fully dormant, but it is a quasi-dormancy that allows the plants to live a long time without water. Trimming the leaves keeps them looking cleaner and saves a lot of space.
Second, in some climates, particularly those with rainy or humid summers, bearded iris are more prone to disease. The plants will be weakened temporarily by transplanting, giving diseases like iris leaf spot fungus an opportunity to spread. So if you see a significant number of streaks or brown spots on the leaves even before the plants are transplanted, cut them back halfway or more to remove some of that diseased tissue. In climates with dry, warm summers, this is not likely to be a concern.
In all other circumstances, I would make this your standard: after you transplant iris, you want the fans to stand up. Iris are adapted to hold their leaves perpendicular to the sun at midday to keep cool and avoid water loss, and fans that tip or flop over will scorch and brown. If they’re tipping over, cut them halfway down or low enough that they stand up. If they’re standing up already, it’s not necessary.
Planting
To plant your iris, dig a wide, shallow basin of the desired with and 2-4 inches deep. Pile the soil to the side. Place your prepped iris divisions in the basin about 6 inches apart at the tips, with the fans pointed outward—this is the direction they’ll creep along the ground as they resume growth, and this way they’ll spread away from each other rather than getting too dense. After you have them placed, you can invert a couple plants with the fans pointed towards the center of the circle so there won’t be a blank space there.
Replanting divided iris Is very easy. Dig a wide basin 2-4 inches deep, place the divisions pointing outward in the same position they were growing in before, and re-cover with soil. Make sure the leaves are vertical to prevent them from scorching in the midday sun. Water thoroughly to settle the soil and hold the plants in place.
Use the soil you removed and cover the rhizomes. Iris like to creep along the surface of the ground, but if they end up being buried 1-2 inches deep, they’ll be fine. You might find it’s easier to keep them stable with a little soil covering, and subsequent growth will stair-step up to the surface so the rhizomes are growing at the depth that they want. Gently pack the soil with your hands enough to keep the plants from tipping over. Then, you can replace mulch on top.
Should you fertilize or amend the soil?
Bearded iris are tough plants that do well even in poor soil. That’s one of the things we like about them! Additionally, their roots leave channels in the soil when they die, allowing oxygen and nutrients to circulate deep into the garden. I prefer not to collapse those channels by tiling the soil unnecessarily.
However, if it looks like the clump of iris really depleted the soil (indicated by very weak plants at the center of the clump), you can consider sprinkling a little compost on top of the soil to gradually break down and fertilize the iris over time. You should do this after the iris are planted and covered by native soil. It really doesn’t take much compost to replenish soil nutrients and may not be necessary at all. Then spread mulch over the top, and water them thoroughly to settle the soil around the rhizomes and initiate new root growth.
Summary
Bearded iris multiply quickly and the number of fans can triple every year. Clumps that become too dense can start to decline in the middle, and should be dug and divided every 3-4 years.
Bearded iris is hardy enough to be dug or and divided throughout the year, but dividing clumps in June—just after they bloom—gives plants the longest time to re-establish before the next blooming season.
Rhizomes creep along the ground at or just below the surface and form branching shapes that can be split into 2 to 6 inch segments, each containing 1 to 3 fans.
Divisions with large green fans can bloom the next year. Older portions of rhizome that are still firm but don’t have much foliage may take two years to grow established enough to bloom.
Growers in humid-summer climates may want to trim the foliage during transplanting to limit the growth of fungal diseases. Foliage that flops over will scorch in the sun and can be trimmed halfway. Otherwise, if the foliage looks healthy and can stand up straight after the plants are transplanted, it can be left intact, or trimmed part way down to clean it up.
Bearded irises should be planted in clusters in a wide, shallow hole just 2 to 4 inches deep (not including mulch). Arrange rhizomes around the hole, several inches apart, with the rhizomes laying horizontally and the fans pointing upwards. Point the rhizomes in all directions with the majority pointed outward, then cover with soil.
Irises typically do not need fertilizer and can grow in poor, compacted soil. Optionally, you can sprinkle a thin layer of compost on the soil to supply a nutritional boost.
After transplanting, reapply mulch and water the plants in to get them established.
