Is thaw/freeze affecting plants?

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You walk out of your home ready for the day, the sun hits your face, and it is an unusually warm day for February. You rejoice. Spring is here. The next day there is a light fluffy snow hitting you in the eye. For most Illinoisans, we have become used to getting our hopes up, only to realize winter is not done with us.

What does this mean for the plants in our garden? Our trees?

Horticulture educator Chris Enroth said "plants during the winter are dormant, slowing or suspending their processes. Warm temperatures may or may not trigger plants to wake from their winter slumber."

Enroth said "chilling requirements" are a key factor.

"Over the eons, plants have encountered warm winter weather, triggering growth, which then is killed off when the winter weather returns," he said. "To counter the issue, many of our plants developed a chilling requirement. Chilling requirements, often measured in hours, are a period of time during which the plant must be exposed to cold weather (typically below 45 degrees Fahrenheit) to bring the plant out of dormancy."

Fruit trees like apples have more chilling requirements that a peach. Most flowering trees require 500 to 2,000 chilling hours. If the trees have reached their chilling hours, warmer temperatures along with longer day length may cause buds to break and growth to occur earlier than usual. If we were then to get another hard frost, opening buds and young fruit can be extremely susceptible. As of Feb. 27, we are around 800-900 chilling hours, according to the Midwest Regional Climate Center.


The warmer temperatures also will increase the incidence of frost cracking. These longitudinal openings can extend deep into the wood of the tree and tend to be noticed in the spring. This condition is most commonly seen in sycamores, maples, apples, cherries, horse chestnuts, lindens, walnuts and willows. Frost cracks are caused when sunlight warms the bark and inner wood on the south or west side. The bark and inner wood contract at different speeds when temperatures start to lower, causing the bark to split.

Frost cracking may occur because of too much pruning, causing more sunlight to hit the bark, or a tree was recently taken out next to it that shaded it for many years. There is not much a homeowner can do fix frost cracks other than keep the tree heathy.