Some people associate the arrival of spring with when buds form on trees, but really most tree buds form in the summer and then undergo various degrees of dormancy throughout the fall and winter months. What causes tree buds to open in the spring? It is not just the warmer temperatures as you might think. That is a good thing, because a mid – winter thaw could result in tree buds opening and exposing delicate, young tissues to subsequent freezing conditions that they could not survive. It is actually exposure to cold temperatures for certain lengths of time before temperatures warm that trigger the hormonal and enzymatic actions that promote normal growth of new tissues.
Some species of trees need only a few weeks of chilling temperatures, while others need months of cold temperatures before exposure to warm temperatures, which results in the normal growth of bud tissues. For example, certain cherry trees require 1,000 to 1,500 hours of 32 to 45 ⁰F temperatures to reach their chill requirement (aka vernalization), while sugar maple trees, in comparison, need nearer to 2,000 hours of chill time.
Even though trees will not “bud out” during a mid-winter thaw, great damage to fruit crops that experience unusually warm spring weather followed by frost conditions can occur. See the article on Michigan’s cherry crop loss during 2012 here!
Written by Sue Vincent