Q: “I never did get around to pruning my apple trees this winter. Can I prune them now?” Karin Leonard, Pismo Beach, CA
A:>/b> The short answer is, “It depends.” Summer pruning of fruit trees generally suppresses the trees’ vigor by removing leaves during the growing season. If your apple trees are low to moderate vigor, limit your summer pruning and use your time to thin the fruit. This allows the trees to accumulate more of the sugars produced in the leaves while reducing the number of fruits the tree has to support. For vigorous or very vigorous trees that missed their pruning date, summer pruning may be used in combination with other management tools to slow growth if undertaken at the right time. Vigorous trees usually need irrigation and nutrient management to curb their vigor.
Summer pruning of apples may also be used to improve fruit color and quality and control some pests. Fruit thinning and improving light within the tree canopy can improve fruit color and quality. Wooly apple aphid often colonizes the bases of actively growing water sprouts, so thinning these vertically growing shoots can help to control this pest. It's best to delay removing water sprouts until late in the season and avoid leaving stubs that might re-sprout next year.
Many fruit trees can be summer pruned annually. If the branches or trunk are exposed by summer pruning, you should protect the exposed branches and trunk by painting them with a mixture of half white latex interior paint and half water.
Use only good sharp tools: a bypass hand pruner for shoots or small branches and loppers for the mid-sized branches. Dip or spray your tools with a 10 percent bleach solution (1 part bleach, 9 parts water) between trees to stop the spread of any diseases. Dry and oil your tools after use to prevent rust. Leave cuts exposed to the air — wound seal compounds are not recommended.
For more information on the timing and methods for summer pruning of apples and other types of fruit trees, contact the Master Gardeners. Happy pruning.