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.
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.
