A 72-degree Tuesday followed by a 21-degree Wednesday on top of a record-warm February: Even by Chicago standards, recent weather has been extra erratic.
Snowdrops and witch-hazel were blooming and daffodil foliage was up 6 inches in many places after a month of super-warm days when a sudden sharp freeze struck. It’s a reminder to Chicago-area gardeners to take nothing for granted, said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle.
“Our weather has always been variable in late winter and spring, but this year the see-saw between warm and cold has been extreme,” he said. “It’s another indication that our climate is becoming more volatile and unpredictable.”
He urged gardeners to be cautious, even on sunny T-shirt days. “Don’t be too quick to get started on the garden season,” he said. “Tomorrow could be very different.”
Here are some tips from the Plant Clinic for gardening in this fickle season.
Watch the weather, not the date. “The calendar means nothing this year,” said Sharon Yiesla, plant knowledge specialist. “What matters is the 10-day forecast.” Some plants bloomed or sprouted weeks early in February, but cold weather in March could stop them in their tracks. “Budburst on flowering trees and shrubs could come early, but we don’t really know,” she said. “It will depend on the day-to-day weather.”
Beware the freeze. The biggest danger at this time of year is that warm weather could be followed by sharp, plant-killing freezes. “The longer your plants stay in their winter dormancy, the safer they will be,” Yiesla said. Soil that warms up too soon can trick plants into coming out of dormancy too early for safety. To insulate the soil and keep it cooler, leave layers of mulch or fallen leaves in place on garden beds. “If you do rake leaves off of garden beds, keep them handy so you can spread them out again to protect sprouts if freezing weather is predicted,” she said.
Relax about spring bulbs. “These are tough plants,” Campbell said. Crocus and snowdrop blooms are not likely to be damaged by a little snow or a few degrees of freezing. Daffodil and tulip foliage is thick, substantial and relatively cold-resistant. Even if leaves that sprouted weeks ahead of the usual time do get nipped by frost, the flowering is not likely to be affected.
Check if you need to water. Plants use a prodigious amount of water in springtime to open their buds, push up their sprouts and unfurl their leaves, and not every area will get enough rainfall. “Feel the soil,” Yiesla said. “If the surface is moist, there’s no need to water. If it feels dry, dig down an inch or two, and if it’s still dry, water.”
Be wary about pruning oaks and elms. Because they are subject to some easily spread pests and diseases, oaks and elms should only be pruned when they are dormant, usually between October 15 and April 15. “This year, the accumulation of warm days has brought these trees very close to coming out of dormancy weeks early,” Campbell said. “Any day now, it could be too late to safely prune oaks.” If you are considering having an oak or elm pruned, first check with the Plant Clinic (mortonarb.org/plant-clinic) to see whether it can still be done without a great risk of spreading deadly pathogens.
Prune roses. While the plants are still dormant, use sharp, clean pruners to remove dead wood, control the shrub’s size and shape, and cut stems back to encourage new growth. Start vegetable gardens with extreme caution. If your soil has thawed and you have a cold frame to protect young seedlings against cold snaps, you can probably sow seeds of cold-tolerant vegetables such as spinach, cabbage, carrots, kale, radishes and beets. Warm-season vegetables such as tomatoes, peppers, eggplants, melons and zucchini should be started indoors under lights. “Plan to transplant them outdoors as usual after the middle of May,” Campbell said.
For gardeners who want to know, “Is spring here?” or “When can I plant?” the Plant Clinic’s answer is “It depends. The weather rules.”
“Our climate has changed and the old wisdom about what to do when is out the window,” Yiesla said. “The best advice we can give gardeners is to pay close attention day by day.”
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.
