Warm spells in late winter can tempt winter-weary gardeners to start work in the garden too early.
"Even though the air is warm and people may be wearing T-shirts, most plants are not yet ready for spring," says Doris Taylor, Plant Clinic manager at The Morton Arboretum in Lisle.
Buds may be swelling on trees and shrubs, but the soil is still cold. That's a good thing, Taylor says, because it will keep plants from sprouting too early — which would put them at risk from the next freeze.
In the Chicago region, hard freezes are likely in February and March, Taylor says. "That's a big reason why we spread mulch on beds and around trees and shrubs," Taylor says. "It insulates the soil and keeps it cold, so plants will stay dormant until it's really time to start growing."
The lack of snow this winter leaves plants more vulnerable than in years when it snows more, Taylor says. A layer of snow on the ground insulates and protects plants against bitter cold weather.
What if plants such as spring bulbs do start to sprout? You can protect the green tips from frost by covering them with an inch or two of lightweight mulch, such as leaves, she says.
If a deep freeze does strike the foliage of bulbs and other plants, it probably will only harm the leaves and not the flowers, which are not likely to have emerged yet. Bulb plants should bloom on time, even if their leaves are discolored or shriveled. Those that normally bloom early, such as snowdrops and snow crocus, tend to be more resistant to frosts, Taylor says.
It's important not to walk on lawns and garden beds during these warm spells, she says, much less start digging. Soil that is beginning to thaw is likely saturated with water and can't drain well, because there is a layer of frozen soil underneath.
Walking on wet soil can compact it, squeezing the soil particles together, so no air or water can flow between them. That causes big problems for plant roots.
One thing you can do in late winter is check perennial beds for frost heave — plants that have been thrust out of the ground by the freeze-thaw cycles of a Chicago winter. "Gently press the plants' crowns back into the soil," Taylor says. To avoid compacting the soil, step only on garden paths or on steppingstones that will distribute your weight.
You also can cut back clumps of ornamental grasses and prune shrubs, if you can do so without compacting the soil around them.
Otherwise, "this is a good time to start vegetable seeds inside under lights," Taylor says. "Wait a few weeks to start working outdoors."
Beth Botts is a staff writer at The Morton Arboretum in Lisle (www.mortonarb.org).
For tree and plant advice, contact the Arboretum's Plant Clinic (630-719-2424 or firstname.lastname@example.org).