I have written several articles on pruning fruit trees and each time I suggest pruning them between February and the end of March, depending on the weather. This is one spring where pruning fruit trees may not end until the end of April. I have tried to prune apple trees several times, only to go through the crust and deep snow.
The Minnesota Extension Service states apples, flowering crabapples, pears, mountain ash and hawthorns should be pruned within a certain timeframe. They claim one can start pruning fruit trees once they go dormant in the fall. Some claim that to start pruning too early in winter can cause severe winter damage. This is the reason most apple growers don’t start pruning until February.
Pruning before the growth starts in the spring minimizes the spread and chance of infection by the bacterial disease called fireblight.
Another variety of tree that should be pruned at a certain time of the year to avoid disease invasion is the oak tree. Oaks should be pruned during the months of December through February to minimize the chances of oak wilt infection, which is a fungal disease. Any summer pruning of oak trees due to storm damage should be covered immediately with some kind of wound dressing.
Some trees have a free flowing sap and will bleed if pruned in late winter or early spring. Although this bleeding causes little or no harm to the tree, it causes major concerns for many homeowners. To prevent bleeding, this group of trees can be pruned anytime they are actively growing and early in the season is best. The bleeding trees include all maples, including boxelder and honeylocusts, and they should be pruned during dry periods in the summer. Other bleeding trees include butternuts, walnuts, birch, ironwood, blue beech and elm.
Before pruning make sure all pruning tools have been cleaned and sharpened. A sharp pruning tool will prevent tears in the bark and make the cuts with less effort. For more information on pruning trees, the proper tools and the best time to prune, you can visit http://www.extension.umn.edu/stribution/horticulture/DG0628.html.