As an expert in pruning, I can tell you that it is safe to trim trees and shrubs once dormancy has set in and all the leaves have dropped. This is especially true for fruit trees with overly large flowers, as pruning during the right time of year will help them produce more flowers and fruit when spring returns. However, it is important to be mindful of the climate when pruning. Horticulturist April Johnson, gardening coordinator at the Rodale Institute, advises against pruning when it is humid outside.
The moist climate encourages the growth of microbes that will take full advantage of the damage caused by pruning. Wait for the sun to come out; it dries out and kills mold and bacteria. The best time to start pruning is when the plants have completely shut down and have been totally inactive during the winter. This usually happens after all the leaves on the plants have fallen and the trees have been exposed to three or four episodes of very cold temperatures and severe frosts. For this area of the country, that usually means the end of December or the first of January.
Trim deciduous shrubs that grow primarily for their foliage, such as the golden smoke tree, almost any time except late fall. New growth that begins after pruning at the end of the season will be too tender to survive the winter. If you want to carry out significant pruning, it is best to cut the shrub when it is dormant in winter. The goal of pruning fruit trees is to open up the tree so that more light can come in and a better harvest of fruit, instead of obtaining maximum flowering. According to The Southern Living Garden Book, to keep plants clean and compact, cut between a third and a half each year just after flowering.
Make sure the plant has time to prepare before winter arrives.
