By Marisa Thompson
Fog and ice created this wonderland effect and coated everything in Las Vegas in March 2018. Once it melted, it didn’t amount to enough to skip an irrigation event. Photo by Marisa Thompson.
Most of us don’t garden much in the winter months, but that’s not to say gardening in winter can’t be very productive. Cold frames, hoop houses, and frost cloth are excellent tools for extending the season—protecting veggies past the first frost in fall and before the last frost in spring. Depending on where in the state you’re situated, it might be warm enough to plant bok choy in January and make kimchi in March, even without season-extension contraptions (although a polar vortex might wipe out even the cold hardiest of plants). Some varieties of beets, carrots, lettuces, and brassicas (e.g., kale and brussels sprouts) can continue to thrive after exposure to temperatures down around 20°F, and parsley is famous for staying alive down to 10°F. Whether your winter veggies are keeping you busy or you’re twiddling your green thumbs in anticipation of spring planting, now is a great time to focus on the perennial plants in your yard.
Annual plants are those that can complete their full life cycle in one growing season, from a germinating seed to a plant that flowers and produces its own seeds. Annuals, like tomatoes, corn, and squash, can’t survive New Mexico winters. Perennials, on the other hand, last through the cold months and continue to grow into future seasons—that is, as long as we pick species that are cold hardy, and as long as we take care of them.
Most people’s tendency is to forget about perennial landscape plants in the winter and to assume that, because they’ve lost their leaves, they don’t need any care. The truth is, all perennials, from trees and shrubs to vines and grasses, have active roots during the winter, even if they’re dormant and leafless above ground. I surveyed local experts on their biggest concerns regarding winter gardening, and the answers were unanimous: winter watering, mulching, and protecting young trees from a type of trunk splitting known as “southwest injury.”
While severe water stress can kill plants in the summer, it can also hurt them in winter, just more slowly and less conspicuously. The telltale signs of winter desiccation, like branch dieback, may not show up until things green up in spring. To avoid winter desiccation, we need to water less frequently, but it’s important to always water to the same depth, no matter what time of year. Remember, when watering in winter, choose warm days, and be sure to disconnect and empty watering lines so they don’t freeze and burst in the night. Water slowly to limit runoff and hazardous ice patches.
How often should we water? From December to March, water about once a month for trees, shrubs, flowering plants (like penstemons and catmint), groundcovers, and warm-season turfgrasses. Twice-monthly irrigations are suggested for cool-season turf (e.g., Kentucky bluegrass). And desert plants that are more drought tolerant can make it through the winter without supplemental irrigation. For detailed guidelines, see the infographic below, created by the Albuquerque Bernalillo County Water Utility Authority.
Where should we water? When newly planted, it makes sense to water right at the base because we know that’s where the root ball is. But as plants become established, the majority of active plant roots grow outward laterally from the main stem. This means we want to apply irrigation water at the canopy drip line and beyond to encourage healthy, lateral root development, which can extend more than twice the plant’s height.
How much should we water? There is no easy answer for this question because it depends on soil type and irrigation system, as well as plant type and weather. Regardless of your system’s setup, the goal is for the water to seep down slowly, and watering depths should be kept relatively constant throughout the year. An easy way to estimate how deeply you’ve watered is to push a long screwdriver down into the soil in a few spots. It will move easily in moist soil and become harder to push when it reaches dry soil. This technique sounds too simple to be true, but it’s recommended by all of the local gardening greats.
Mulch to be Desired
Mulching is also important for gardening, including in winter. Make certain when you water that it is getting through the top mulch layer and soaking the ground underneath, getting deep enough to reach all the roots and at least a little beyond. Checking under the mulch to ensure the soil is dry before watering is a recommended practice, no matter what time of year.
Whether you’re planting in the ground or in containers, mulching on top with any fibrous organic material (e.g., straw, leaves, woodchips, pine needles, pecan shells) will help in multiple ways. Four or more inches of mulching material helps suppress weed germination and growth, holds moisture in the soil, keeps the rooting area warmer in winter (and cooler in summer), prevents water and wind erosion, and prevents surface crusting (which inhibits water penetration). Over time, mulching also provides much-needed nutrients that feed beneficial soil organisms, increases organic matter, and improves soil texture, eventually enhancing the soil’s ability to store nutrients for plant root uptake. Of course, if you’re direct-seeding your garden beds or containers this spring, adding a thick layer of mulch too soon can inhibit seed sprouting. You can either transplant seedlings and add mulch around them or scoot the mulch away in the spots where you’re planting seeds.
Trunks in Training
A final concern for the winter gardener is winter sunscald (aka “southwest injury”) on trees. Have you ever noticed bark buckling off the tree trunk? Or blisters on the southwest side of the trunk while the other side looks fine? Go outside and take a look for yourself. Sometimes the differences are shocking.
What happens, in short, is that bark on the southwest side of the trunk is exposed to afternoon sun, and the sap gets warm enough that it starts moving in the tree. Normally this is fine, except that on especially cold nights following super sunny days, the cells carrying sap rupture, like soda cans in the freezer, causing irreparable damage. This is particularly a concern on trees with thin bark—often younger trees, or species like honey locust and apple. Winter sunscald is especially a problem in climates with intense sun exposure and extreme fluctuations between daytime and nighttime temperatures, like we have in New Mexico.
Painting the trunks of trees with diluted white latex paint (do not use oil-based) is an easy way to protect the trees from winter sunscald because the white surface reflects more sunlight and the trunk stays noticeably cooler. Use water to dilute the white latex paint to half strength. It goes on easily, so go ahead and include lower branches—the blistering effects of southwest injury can be found on unprotected branches too. As the paint is exposed to the environment (and the tree grows), it will naturally fall away.
Another option, if you do not want bright white tree trunks in your landscape, is a light-colored trunk wrap that is loose enough to allow airflow and does not dig into the bark (white paper or even newspaper will do). Please note: A clear or dark-colored wrap is not recommended. To be safe year after year, loosely wrap your trunks when the trees go dormant in December, but do not forget to remove the wraps each spring.
In a state like ours, where we receive abundant winter sun and scant precipitation even in non-drought years, paying attention to winter sunscald, mulching, and irrigation in the off-season will pay dividends throughout the rest of the year. Keep these tips in mind and your perennials will be raring to grow come spring.
An Inexhaustive Snapshot of Regional Seed Resources
Native Seeds/Search (Tucson, AZ) is a nonprofit seed conservation organization that preserves and sells many arid-adapted vegetable, grain, and flower seeds, many of which originated in what is now New Mexico. nativeseeds.org
High Desert Seed and Gardens (Montrose, CO) provides a nice selection of open-pollinated vegetable, flower, herb, and grain seeds adapted for high-altitude desert gardens. highdesertseed.com
Painted Desert Seed Company (Sanders, AZ) provides open-pollinated seeds adapted to high-elevation desert gardens. painted-desert.com
Epic Seeds (Albuquerque) offers a limited catalogue of heirloom vegetable seeds, especially from New Mexico and Guatemala. epicseeds.com
J&L Gardens (Española) sells at local farmers markets and offers over 500 varieties of heirloom and open-pollinated vegetable seeds. jandlgardens.com
Plants of the Southwest (Albuquerque and Santa Fe) is a great resource for native grass, wild flower, and open-pollinated vegetable seed. plantsofthesouthwest.com
Seeds Trust (Littleton, CO) is a thirty-year-old seed company offering an extensive catalogue of open-pollinated, heirloom, and organic seeds grown in and adapted to the high-desert West. seedstrust.com
Rocky Mountain Seed Alliance (Cornville, AZ) is a regional nonprofit supporting seed stewardship, education, and networking. rockymountainseeds.org