Every spring we seem to have at least one spell of freezing temperatures and snow that occurs well into April, May or even June. That is not surprising when one lives at 4,200 feet in elevation. Unfortunately though, if the fruit blossoms are open they freeze and we have no fruit that season.
If the fruit blossoms are destroyed by freezing temperatures, how do the winter buds on the trees survive bitter cold and howling winds? Winter buds form late in the summer, overwinter and then open in the spring to form leaves and flowers. Hard scales cover the buds and protect them from the elements. In addition the buds are dormant and not active during the winter, which also helps protect them. Once the fruit blossoms or other flowers are formed they have lost their protective dormancy and covering.
A plant hormone, abscisic acid (ABA), is produced by the plant. Abscisic acid serves several functions in trees, including the induction and the maintenance of dormancy in buds. Without going into the biochemistry of what happens, let it suffice to say that ABA is produced in the terminal buds of the tree in preparation for winter. This slows the growth and activity in the bud and directs the development of scales to protect the bud during the winter. In the spring (length of daylight is a strong trigger) the abscisic acid becomes diluted and the buds open.
Winter buds (in addition to the bark and twigs) are used for identification of trees during the winter when there are no leaves. I will admit, when attempting to identify a tree in the winter one of the first things I look for are dried leaves at the base of the tree. I admire those with the skills to recognize winter trees when no leaves are available. There are several books on winter buds available, including “Winter Buds”, an out of print volume by Betty J. Davis. Stop and take a good look at the different winter buds on trees – they come in such a variety of shapes and colors and are quite fascinating.
These pictures show a few of the winter buds in our yard (Modoc County CA).