- Author: Jutta Thoerner
- Editor: Noni Todd
Bud Break
By Jutta Thoerner Master Gardener
While my stone fruit trees are looking good, my pear tree has not budded out yet. It is May. What is the problem? Suzie in San Luis Obispo
Your pear tree might be suffering from “delayed bud break”
You know that all deciduous fruit trees have a period of winter dormancy, the stage between leaf drop in the fall and bud break in the spring, which protects the tree buds from freezing weather. Scientists have identified two distinct stages: endodormancy is the 1st stage and is related to limiting growth factors in the tree buds. Ecodormancy, the 2nd stage, is related to external factors - temperature which controls growth.
Stay with me, because this lifts the veil of the dormancy mystery! So, in order to wake up your pear tree, a certain amount of cool weather is needed during the 1st stage. We refer to this as a chilling requirement. Different varieties need different amounts of cold hours, roughly between 30 degrees F and 60 degrees F. Stone fruit trees, apricot and peach, need an average of 700-1000 chilling hours below 45 degrees F. Pome fruit trees, pear and apple, need an average of 1000-1500 chill hours. The chilling hours are needed to end the 1st stage of winter dormancy. In the second stage of winter dormancy (ecodormancy) warm temperatures “wake up” the buds and the tree starts budding, then blooming. Just as the cold temperature is needed to facilitate the end of the 1st stage, the warm temperature is needed to begin growth and bloom. To achieve a timely and complete bud break, cold winters and warm springs are needed. The unusual weather this year might have contributed to the delayed bud break on your pear tree; not enough chill hours during the dry warm winter, followed by unusual cool temperatures with cold winter like storms in April. There is a good chance that your tree will catch up with the warmer weather we are having now.