
Originally Posted by
Hummer
Horticulturally, pruning trees in summer is not the best practice. If necessary, you can prune trees any time but it's better to wait until they become dormant in late fall or winter after a month or so of frosts. Pruning during the growing season does open trees to a wide variety of insect pests and diseases that are better avoided. Cuts cause sap to flow out, sapping energy from the tree and attracting insects. Blight includes a number of bacterial infections that attack open wounds and can kill many species of trees, not just fruit bearing trees like apple, crabapple or miniature crab, and blight and fungal infections can be difficult and costly to treat.
Also, pruning trees during the bird nesting season is not good. This year I've twice rescued nestling birds where branches were cut from ash trees by clueless landscapers. In both cases I was able to save the nests by re attaching them to a nearby limb.
Wait until December to do major cuts with a thin bladed pruning saw, then follow up with good sharp loppers. Start from the top down. Stand back and look at the shape to determine what shape works best for the type of tree and location. Usually, just thinning will do the job by taking extra branches off the lateral limbs to bring light and health into the tree.