Dormancy occurs when trees begin receiving less light and experience temperature drops. These changes in environmental conditions allow trees to “know” that winter is coming and begin to prepare. Trees take their remaining nutrients and begin to seal themselves off from their leaves before dropping them in the fall. Leaves in certain plant species (such as deciduous trees) fall due to plant hormones producing chemicals that signal the leaves to break off. These hormonal chemicals also prevent cell division and cause trees to stop growing.

This process allows the tree to conserve energy and lowers its need for water and nutrients. Mulching in the fall helps insulate a tree and reduce moisture loss during winter dormancy.

For most trees, this time of rest is the best time for pruning. Trees are less likely to be “shocked” by the activity and wounded limbs. Pruning also helps prevent potential dangers that weak or damaged branches pose, especially during strong winter winds. Any wounds from trimming and pruning will heal more quickly since the tree is expending no energy on new growth, so the tree will be less likely to become infected from disease or insects. In addition, since the ground is frozen, less trauma due to compaction occurs.

Inspection during winter and spring dormancy is a great idea because tree professionals can more easily see the tree structure and unobscured bark. Areas of decay or injury will be more easily recognized.

Evergreen trees experience dormancy as well but in a different way. Their needles become coated with a heavy waxy substance that prevents them from losing moisture. In addition, they have a chemical inside that helps them resist freezing.