In the gray of winter, we’ll be grateful for the color of our evergreen trees and shrubs.
“It’s cheery to see those touches of green from plants that don’t go entirely dormant,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. The flip side is that because they’re not dormant, these plants have needs and vulnerabilities all year long.
Help your evergreens stay healthy and withstand the cold and the drying winds of winter by taking these steps in autumn.
Water evergreens until the soil freezes. The more water they can store in their leaves, needles and branches in fall, the better they can resist drying out over the winter. Evergreens are especially vulnerable because they stay green and continue to use water for photosynthesis whenever it’s not too cold.
“Water the soil around their roots slowly for a long time, so it can really soak in,” Yiesla said. One good method is to lay the hose right on the soil inside the drip line — that is, in the area beneath its branches — with just a trickle of water coming from it, and leave it there for half an hour or so. Move it to different parts of the area from time to time.
“While you’re watering your evergreens, remember also to water any other plants you’ve installed in the last year or two,” she said. “They need autumn watering too.”
Spread mulch. A good layer of wood chips or leaves spread around an evergreen will insulate the soil and roots against temperature fluctuations, including warm spells as well as deep cold snaps. Make the mulch layer 3 to 4 inches deep over an area that is at least 4 or 5 feet across.
Spread the layer evenly without piling it against the plant. Mulch that is heaped around the trunk can trap moisture and lead to rot, or harbor small animals that eat bark in winter.
Look for salt hazards. The salt and other chemicals used against snow and ice on sidewalks, driveways and roads damage evergreens and other plants because they pull moisture from plants’ tissues. Trees and shrubs that are fully dormant, with bare branches, are not as vulnerable, although their roots can still suffer from salt.
Salt reaches plants’ roots when salty meltwater runs off into the soil from pavement, or when you shovel snow that contains salt and dump it onto plants. Another source is the salty spray thrown up by the wheels of cars and trucks going by on roads where salt has been spread to melt snow or ice.
Damage from salt is easy to spot on evergreens if many needles or leaves turn brown and dead only on the side facing a road or sidewalk.
To help your plants, plan to minimize your use of ice melters in winter and be careful where you dump the snow you shovel.
Don’t stress about fallen needles. It’s normal for evergreens such as pines, firs and spruces to discard their oldest needles every fall. “Depending on the species, each needle lives for only two to four years before it falls off,” Yiesla said. New needles, which are actually a kind of leaf, will grow in spring.
On any branch, the needles closest to the trunk are the oldest. “If needles are brown at the branch tips or only on part of the tree, it may be a sign of a problem,” she said. “But as long as needles are falling from the inner parts of all the branches, it’s just a normal part of the life cycle of an evergreen.”
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.
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