Hartley Magazine

All the latest news, hints, tips and advice from our experts

Is it warm yet?

Ah, what a difference a year makes. Last year, during a freakishly warm spring, flowering trees and shrubs all over the Midwest were in bloom by the end of March. This year, only witch hazels are blooming, all the other trees and shrubs are still dormant. The average temperature in Illinois for March 2012 was 51 degrees; this year, it was about 34 degrees.

The good news is that last year’s drought appears to be over. Until January it looked like the drought was only deepening, but since then we’ve had a bounty of snow and rain, which has brought our soil moisture up near normal. Of course, that could change any time. I remain wary.

If human beings have a hard time adjusting to the weather, imagine how our plants feel. Plants in the ground, especially native plants, have a certain degree of ability to adapt to the weather, like those trees that are waiting to bloom until they get the right temperature signals. But the plants we raise indoors—the seeds we sprout or cuttings we root under lights or in greenhouses—are totally unprepared for what they will run into outdoors. They’ve grown up in an unnatural atmosphere of stability, with constant temperature, ample light, reliable moisture and no wind or storms.

And then we send them out into the garden, where it can be 50 during the day but 30 at night, where it can be 20 degrees colder the next day, where clouds can obscure the sun for days on end, where wind can wrench their stems and heavy rainfall can pound on them.

There are two ways gardeners can make it easier. First, we can wait until it’s really time to plant things out. Gardeners who know the average last frost date for their areas often forget that those dates are averages, taking in a wide range of possibilities. Where I garden, for example, over the last 20 years or so, the date of the last 32-degree frost has ranged from March 27 to May 12.

So a wise gardener uses the average last frost date as no more than a general guideline and pays more attention to this year’s actual weather. Since it’s been such a cold spring—the soil is still frozen at the start of April in much of my garden—I’ll assume the soil will take extra long to warm up and I’ll be waiting a few extra weeks to risk my plants outdoors.

The second thing a gardener can do is called “hardening off.” Basically, we let our plants get used to the outdoors gradually. Once I’ve decided it’s safe to think about planting my more cold-tolerant seedlings in the garden, I will take them outdoors for a few hours each day. Every day they’ll spend a little more time outdoors. After about a week, I’ll figure it’s safe to plant them in the ground. I’ll do the same thing with the more tender plants a couple of weeks later. And I’ll also do it when I buy flats of annuals from the garden center.

During this time, the plants will adapt to the colder and more varying temperatures. They’ll respond to the buffeting of wind by growing stronger cells, and the leaves will grow thicker too. The result will be less risk of transplant shock and plants that are more likely to be able to handle whatever the season throws at them.