How to protect garden plants from winter damage
As winter cold swirls about us, we can retreat to the protection of storm windows, quilts and puffer jackets. Our trees, shrubs and perennials just have to stand there and take it.
Will they be OK? “They’ll be fine, as long as they’re the right plants,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. “Plants that are hardy in places that have cold winters have adaptations that prepare them to survive rough weather.”
Many of our plants are dormant in winter, in a kind of sleeping state that slows down their life processes so they can basically duck out on the rough weather. Dormant trees and shrubs have shucked their leaves, and most perennials have abandoned everything except their roots. In spring, the roots will sprout new stems, leaves and flowers.
“The roots are safe in the soil, which is a great protector,” Yiesla said. It may seem paradoxical, but frozen soil shields roots from winter air that can be even colder. The roots themselves resist freezing by having a high concentration of sugar in winter, which lowers their freezing point. Some have proteins that function as a kind of antifreeze.
When snow falls, it’s an additional layer of protection. “Snow is a great insulator because it’s mostly air,” Yiesla said. “Unfortunately, we can’t count on snow in the winter, especially as the climate is changing and making our weather more erratic.”
Gardeners can step in to protect plants by spreading a layer of mulch over their plants’ roots. Mulch will insulate the soil, keeping it at a steady temperature, avoiding extremes of both cold and warmth. “Sudden warm spells in late winter are a major danger to our plants,” Yiesla said. “Unless the soil is insulated, a day in the 50s or 60s can warm up the ground and trick plants into coming out of dormancy.” Premature sprouts or buds that opened too soon will be vulnerable when the weather changes, as it will, and the cold strikes back.
If you didn’t apply mulch in fall, you can still spread it in winter to protect against those warm spells.
“The important thing is to make a wide, even layer,” Yiesla said. It should be about 1 or 2 inches deep over perennial beds and about 3 inches deep over the roots of trees and shrubs. “Never pile mulch against the trunk of tree,” she said. “That can harbor disease and cause other problems. Instead, rake mulch out in an even layer that covers as much area as possible.”
In a bad winter or a cold snap, the plants most likely to suffer are those that are marginally hardy in Zone 5, such as boxwoods, rhododendrons and bigleaf hydrangeas. “The most important thing a gardener can do to protect plants in the winter is to choose them carefully,” Yiesla said.
Make sure you only install plants that are truly hardy enough for the full range of potential winter weather in Chicago. “Plants can fool you,” Yiesla said. Those that come from slightly warmer climates can seem hardy if they make it through a mild winter, but the next winter may be much worse. “It just takes a day or two of subzero weather to kill a marginally hardy plant,” she said.
On a cold winter day, snuggle up to your laptop on the couch and do some serious research about beautiful plants that will be tough enough for a Chicago winter. “That forethought is the best protection you can give your garden plants,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
