Runners in T-shirts, romping dogs and nesting songbirds all have enjoyed the long stretch of warm days this February. Some gardeners, though, have been anxious that the warm weather may be throwing their plants out of whack.
It depends on the plant, but in general, plants will only suffer if the warm weather is followed by a hard freeze, said Doris Taylor, manager of the Plant Clinic at The Morton Arboretum.
“Warm spells in January and February aren’t unusual in Chicago,” she said. “Most plants will take it in stride.”
The varying weather of spring always affects the time that plants bloom and leaf out, and this spring will be no different. If plants have already starting blooming or opening their leaves when a hard freeze hits, the flowers or leaves can be damaged. That’s why most plants wait until later to protect their buds.
Native plants, which evolved in Chicago’s volatile weather, usually stay dormant, in their winter resting state, until the danger is safely past, said Ed Hedborn, manager of plant records. Plants that come from Europe, where the springtime warmup is typically steadier and more gradual, are more easily fooled. For example, leaves of the European beech tree (Fagus sylvatica) are sometimes deformed by a late hard frost.
Temperatures in the high 20s won’t do much damage, but a bone-chilling freeze to 15 or 10 degrees would likely mean we will see fewer flowers this spring, he said.
If you have a layer of mulch on the ground, it will insulate the soil against warming up prematurely, said Sharon Yiesla, plant knowledge specialist at the Arboretum. That helps keep plants on schedule.
There are some signs of spring. Vernal witch hazel and snowdrops are blooming. They’re not ahead of schedule, though: Snowdrops can sometimes bloom as early as January. “They’re called snowdrops for a reason,” said Hedborn.
What should you do in the garden during this early spring weather? Here are some tips.
Leave winter protection in place. Hard freezes are still possible, so if you protected roses or other plants with leaves, mulch or burlap, keep them wrapped up, Taylor said. The layer of mulch over your garden soil and around trees and shrubs should stay in place all year. You can add mulch any time.
Protect bulb foliage. If daffodils or other spring bulbs have sent up green shoots, cover them with the dried-up leaves scattered around your fence or garage, Yiesla said. That will protect them against colder weather. Even if the green tips are damaged by a freeze, it won’t affect the flowers, which are still safely underground.
Don’t prune maples, birches, elms, magnolias or walnuts. These plants’ sap is already running, and it will ooze from pruning cuts. If they need pruning, wait until midsummer.
Do prune other shrubs and small trees. Now, before the leaves emerge, is a good time to shape up most shrubs and small trees such as crab apples. Look for damage such as broken branches from winter winds.
Check perennials. The thaw-and-freeze cycle of a Chicago spring can sometimes push recently planted perennials out of the ground. “Gently push them back into place,” Taylor said.
Don’t walk on wet soil. If the soil is soft and moist, walking on it can pack it down, so oxygen and roots can’t penetrate it. This applies to lawns too: Resist the urge to do lawn work now. It’s too early to apply crabgrass preventers anyway, Yiesla said.
Enjoy the early blooms. If your flowering shrubs start blooming early, you can’t stop them. “Enjoy them,” Taylor said. “Bring them in the house, and put them in a vase.”
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 email@example.com).
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