Winter can be absolutely punishing on garden plants and soil. In a particularly brutal winter, frost heave appears nearly everywhere, cracking soil and lifting shrubs; plants that typically overwinter don’t survive; rhododendrons get beat up; rabbits chew above-the-snow stems of blueberry shrubs to the ground, and evergreens brown-out. A lot of work awaits a gardener in spring after a winter like that, but damage to plants and soil can be reduced if you do a little extra preparation in late fall.
How winter weather damages your garden
Harsh winter weather damages plants via freezing, hungry animals, desiccation from winter sun and wind, and the salts you use to deice your sidewalks. This is especially true of young plants. A plant’s odds of surviving the abuse of winter depends on its age and health going into the season. If plants are well-established, well-nourished, well-hydrated, and free of insect damage and disease, they have a good chance of surviving. If you allow vulnerabilities, nature will take advantage of them.
But there’s also a new consideration: gardeners have been seeing plants overwinter in our landscapes which didn’t do so before. For me, it’s been morning glory and sometimes basil seeds surviving winter in Zone 7, along with Calla lily bulbs and others which typically have to be lifted in late fall. In the last ten years, we’ve also seen certain species of trees migrate north into zones in which they never overwintered before. Unfortunately, there’s no way to know if you’ll be punished by another Polar Vortex or have a mild winter in which everything wanted and unwanted survives. So if you have tender plants and bulbs, lift them for the winter, even if they’ve survived previously.
How to protect plants from winter weather
Wrap sensitive plants with burlap, especially those vulnerable to winter wind damage. This doesn’t mean that you literally wrap the plant like a Christmas gift. First, sink heavy-duty stakes around the plant, safely outside of the root zone. Then wrap burlap around the stakes, surrounding the plant, with 6 inches between the burlap and the plant. Burlap gets heavy when saturated with water, and it will definitely freeze – having that weight and temperature in contact with your plant is not a good idea. Wrapping the burlap around the stakes allows air between the burlap and the plant, providing an excellent buffer against winter winds when storms roll in.
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Mulch soil or cover it with whatever organic materials are handy. Mulch is excellent for insulating soil, protecting it from frost heave, and regulating the freeze-thaw cycle to protect plant roots. A two-inch layer of pine bark mulch around most shrubs should protect them from damage throughout winter. If you missed the window for mulching, or simply forgot, there are plenty of discarded Christmas trees that can be recycled as mulch in January. Cut the branches off the Christmas tree and cut them into foot-long pieces with a pruner or lopper. Place the boughs around the base of your plants, stacked about 6 inches high. If evergreen boughs are not in your future, use finished compost or straw piled 6 inches high, but keep it an inch or two from the stem or trunk. Keep in mind that winter mulch isn’t about aesthetics – it’s about protection. Besides, it’s frequently covered in snow. You can also use pine straw, autumn leaves, or similar organic materials.
Keep deicing chemicals safely away from sensitive plants. Deicers are largely salts, and salts dehydrate anything they touch. As the deicers melt, they get shoveled onto lawns and plants, and splashed on leaves. Be careful where you spread your deicers, and early in spring, if rain is in short supply, saturate the areas closest to the street, driveway, or walks with lots of water to dilute the salts. My strategy is to use no deicing salts at all, but I realize that’s not practical for everyone.
Protect sensitive plants from animals. Deer, rabbits, voles, mice, and all wildlife will eat just about anything if they’re hungry enough. When the ground is covered with snow, the only food available to wildlife is what they can easily find above the snow line. A couple of winters ago, rabbits chewed my young blueberry shrubs to the ground when I wasn’t looking. How disappointed was I to find 6-inch tall shrubs when the snow melted? Now, the blueberry shrubs are safely ensconced in a raised bed, surrounded by 3-foot tall fencing. I’ve also surrounded sensitive plants in my yard likewise. Protect the base of trees – if animals nibble on the bark of young trees and shrubs, disease may infect the plants in spring and at the very least, blooming will be affected. Not to mention the difficulties you’ll have establishing that plant in your landscape, assuming the damage doesn’t kill it outright.
Plants cannot take up water from frozen ground, so they send their roots deeper to find liquid water. If there is sufficient snowfall, hydration isn’t a problem during winter. But during a dry, frigid winter, plants can become significantly dehydrated. This is what causes the browning of leaves in late winter and early spring on evergreens. Water your plants deeply in late fall if you’ve had a particularly dry season.
When the snow and ice finally retreat after a harsh winter, be patient in early spring. If a plant looks sick or even dead, don’t pull it out prematurely. There still may be life in the root system, so give it a little extra time to show its stuff. Bear in mind also that if the soil has been frozen, it will take an extra 1-3 weeks to warm sufficiently to stimulate plant growth. And for God’s sake, don’t fertilize a plant when it’s in that condition, because you’ll kill it.