This article was submitted by the Wauseon Tree Commission.
An individual day of warm weather or a streak of days above freezing in the middle of winter probably won’t make much difference to a tree.
Trees are slightly different from small flowers in that the plant itself probably won’t be affected too badly by a mid-winter thaw – with the exception of fruit trees, whose fruit can be affected quite drastically by this type of thaw, and not in a good way.
All trees go into a dormant state as a normal part of their life cycle every year. In fact, they all need a certain period of cold in the dormant season to break out of dormancy in the spring. A prolonged exposure to temperatures between 20-50 degrees Fahrenheit is what tells a tree to, in essence, reset its clock. Once those numbers of hours are “logged,” the tree is at the threshold of budding and will flower when the first warm temperatures start to hit. This happens in a spectrum, and it varies between species, individual trees, and geographic location.
The problem is when temperatures fluctuate so rapidly – cold, warm, cold. To some extent, trees that are native to the Midwest, for example, will know the pattern and not get tricked. The trees are supposed to have buds. They have buds all winter long. The unusually warm weather is causing some confusion for the trees and other early blooming plants.
Lilacs often get a little green growth early in winter, so they can open early in the spring. Foresters are more concerned about the lack of snow, because that snow insulates the root systems from sub-freezing temperatures. You may notice spring bulbs emerging too early.
To slow emergence, cover with a shade cloth. If you have your bulbs in containers, simply place the containers in a shaded spot or cold shed for the rest of the season. where they are out of the sun and daytime warming temperatures until the warm days pass and winter sets back in. If they are in the ground and have emerged over a few inches, cover them with a generous layer of mulch to protect the new growth the best you can from a deep, long freeze.