Despite a warm winter and early bloom, experts warn it’s too early to think about garden planting

While warmer weather in recent weeks may feel like an invitation to dig into spring planting, experts urge patience for anyone looking to get an early start on their gardens — and caution vigilance for any flora already woken too early as the risk of cold bouts still looms.

“Do not be tempted into planting your garden or putting cold-intolerant plants out months early,” said Christy Rollinson, a forest ecologist at The Morton Arboretum in Lisle. “Although we are seeing more and more signs of spring, we will likely still have several deep freezes left this year.”

Lately, you may have noticed trees starting to sprout leaves or flowers getting ready to bloom, despite the calendar. That’s because unseasonably warm temperatures this winter have signaled to some greenery that it’s time to launch into spring processes ahead of what’s typically expected.

Seasonal growth relies on environmental cues. Ahead of winter, through the summer and fall, trees develop buds that will eventually become the next year’s leaves, according to Rollinson. Those buds remain dormant during the winter and wait for cues, such as an accumulation of warm temperatures, to spur into action.

Many spring-flowering plants are controlled by similar prompts.

With Chicago ringing in its warmest February and fifth warmest winter on record, some trees and plants have accumulated enough temperature cues to tell them spring is here, Rollinson said, triggering growth weeks ahead of normal.

“Peak bloom hasn’t reached the Midwest yet, so we don’t want to make assertions or generalizations that may change as the next few weeks are cooler and closer to normal,” she said.

Starting Sunday, a push of cold air is poised to move through the Chicago area, according to Kevin Birk, a meteorologist with the National Weather Service in Romeoville. Temperatures in Naperville are expected to dip down to 25 degrees Sunday night. On Monday, the projected high is 37, followed by an evening low around 24.

Birk said the area could even see some snow showers Sunday night into early Monday. By mid-week, temperatures are expected to rise again to mid-50s.

At this time of year, Birk said it’s “not uncommon” to get hit with these spurts of colder weather, though he added that as April approaches, those cold shots will become less frequent.

Still, for the time being, he said, “I wouldn’t say winter is over just yet.” That could mean some plants and trees are in for an energetically stressful start to their spring.

Cold snaps after warm weather can be damaging for early blooms, Rollinson said.

“When we have an exceptionally warm winter like we did this year and exceptionally early leaf outs or flowering, there’s a real risk that trees are going to get hit by a deep freeze,” she said. “Because trees can’t heal frostbitten tissue, they have to drop those leaves, drop those flowers and try again if they can. And that is energetically very stressful.

“That means the tree is going into the growing season at a disadvantage.”

For those looking to protect their already spring-kissed trees or plants headed into colder weather, it can be tricky, warned Bruce Black, a horticulture educator with the University of Illinois Extension office. But he offered a few tips for home growers that could help.

Through the next month or so, anything that has started to come up out of the ground should be covered with a blanket or a bed sheet when temperatures risk spring frost, Black said.

If plants are damaged during cold bouts, watch for them they reflower again after warmer weather returns, he said. In those cases, extra fertilizer should be provided so bulbs have the nutrients they need to regrow.

For perennial trees, such as those that bear fruit, it can be hard to protect when temperatures drop, Black said. Hhe advised anyone whose trees have “woken up” to hold off on pruning.

Dormant pruning, experts say, stresses plants less than pruning when they are actively growing in the spring.

For anyone interested in new planting this spring, Black advises caution.

“I know for myself, I have been out working in my garden wanting to plant things. I’ve done some seed starting, and (I’ve been) wanting to put those in the ground because it’s warm, but (I know) that the next round of cold is coming,” he said.

Black did say cold crops that have a built-in hardiness, such as broccoli or spinach, can go in now. As for other greens, he’d hold off until mid-April, he said.

Plants aside, warmer winter weather could have other effects on nature as well.

Insects, like plants, take their cues from temperature rather than daylight, according to Alexandra Harmon-Threatt, an associate professor of entomology at the University of Illinois Urbana-Champaign. This year, that has caused a much earlier emergence of insects and animals, she said.

“Because many insects track their plant hosts,” she said, “earlier emergences of plants will often shift them to become active earlier.”

Harmon-Threatt said she expects bees, beetles, flies, mosquitos, moths and “pretty much all insect groups that emerge in the spring” to come out early.

One insect Illinoisans should be on the lookout for later this year are cicadas. This summer, Illinois will be cicada central as two broods of periodical cicadas co-merge in neighboring areas of the state for the first time in two centuries.

Naperville, however, should only have to worry about one brood, according to Eric Gundersen, nursery manager at The Growing Place Garden Center in Naperville.

He said a second brood will be seen further south.

Chicago Tribune reporter Adriana Pérez contributed.