I generally recommend pruning fruit trees between February and the end of March, depending on the weather.
Last month I tried several times to go through the deep snow to prune apple trees. This year it may not be until the end of April!
The Minnesota Extension Service states that one can start pruning fruit trees once they go dormant in the fall. This includes apples, flowering crab apples, pears, mountain ash, and hawthorns.
Others claim that pruning too early can cause severe winter damage. This is why most apple growers don’t start pruning until February.
Pruning these varieties before growth starts in the spring minimizes the chance of infection by the bacterial disease called fireblight.
Oaks should be pruned only during the months of December through February to minimize the chances of oak wilt, a fungal infection. Any summer pruning of oak trees to clean up storm damage should be followed immediately with wound dressing.
Trees with free-flowing sap will bleed if pruned in late winter or early spring. Although this bleeding causes little or no harm to the tree, it can be a major concern for many homeowners.
Maples, boxelder and honeylocusts should be pruned during dry periods in the summer. Other bleeding trees, including butternuts, walnuts, birch, ironwood, blue beech and elm, can be pruned anytime they are actively growing. Early in the season is best.
Before pruning, make sure all tools are clean and sharp, to prevent tears in the bark.
For more information visit www.extension.umn.edu/distribution/horticulture/DG0628.html.