Jean Keuhn, UM Extension Master Gardener in Anoka County, September 25, 2014
As we begin cleaning up our yards and flower beds, it seems like fall would be a good time to prune the trees, shrubs and plants before they go into winter dormancy, but we would be wrong. Many of our plants should NOT be pruned in the fall, as this tends to encourage new growth that will not be fully hardened off and, therefore, susceptible to winter injury and damaging the plants. Pruning in late winter or early spring allows us to inspect plants for winter damage and see how the plants are doing. Before our plants go into their dormant period (notice I avoid the winter word) the best thing we can do is insure they are well watered. So far this year, we have had plenty of natural water, but don’t let them get dry as the fall progresses.
Fall is a great time to plant trees, but before selecting and planting, find out how big it will be as a full grown specimen. It probably needs to be further from the house than first thought. Also, check where the power lines cross your yard. It is totally appropriate and wise to prune young trees when you plant them. It is also much easier to cut smaller branches. Remove any diseased, dead, or broken branches immediately. Remove multiple leaders on evergreens and other trees where a single leader is desirable. Branches that cross or rub together should be removed. Start your tree strong and healthy and it will bring you years of joy and shade.
Pruning is generally done to control size, improve shape, remove dead branches and improve general growth and flowering of the plant. It can also minimize future problems. Weak or diseased branches are most likely to be damaged in storms, which will further damage the tree. Generally it is better to remove it and not wait for Mother Nature. Try to maintain the natural shape of any plant when pruning.
Established trees are best pruned when dormant, which is late winter, early spring. This minimizes potential for disease as the new growth quickly heals the cut. Do not prune oaks during April, May, or June as this makes them more vulnerable to oak wilt. Spring blooming shrubs and trees should be pruned immediately after they finish blooming to avoid damaging the next years bloom. They can be pruned now, just know the bloom or fruit next spring may be lost. Non-flowering shrubs should be pruned in spring, before new growth begins: Most clematis and shrub roses should be pruned back to live wood in the spring, not now. Hardier shrubs such as spireas and snowball hydrangeas should be pruned to the first pair of buds above the ground.
Older shrubs (like lilacs) with thick woody stems in the center of the plant should have about one-third of the old, thick stems cut out. This allows new stem growth from the roots, keeping your shrub healthy.
Fall brings many garden chores, but pruning is not one of them. So clean and sharpen your tools and plan your strategy for the spring. When it is time for pruning, and you want more information on it, see: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/pruning-trees-shrubs/ .