Trees and shrubs can be pruned to maintain plant health and desired shape, promote new growth, and for safety and security reasons. Most pruning should only be done once a year, but not all plants want to be pruned at the same time.
March is an ideal time to prune many tree and shrub varieties. Late winter pruning occurs after the damaging cold spell of deep winter and ensures the pruning wound will be quickly healed by new growth, lessening the likelihood of disease and drying out. Pruning dormant trees and shrubs makes it easier to choose which branches and stems are to be pruned and encourages a burst of new growth in the spring. Apple trees, including flowering crab apple, oak, honeylocust, and mountain ash should be pruned in late winter to early spring (Feb.-April).
Maples and birch can also be pruned in late winter. They will produce a stream of sap from the pruning wound that will stop once the tree has leafed out. If this is a concern, these trees can also be pruned in late spring or early summer after the trees have leafed out.
Shrubs and trees that bloom in the spring develop their flower buds the previous year and should be pruned after flowering. Earlier pruning removes flower buds and reduces the number of blooms.
After spring-flowering shrubs and trees have bloomed, trim to maintain desired size and shape and to promote new growth. This category includes early blooming spirea, azalea, forsythia, lilac and magnolia.
Shrubs and trees that bloom in early summer should be pruned late winter or early spring – late February through early April. These shrubs and trees bloom on new growth, and pruning encourages new stems for even more buds and blooms.
Pruning hydrangeas depends on the type of hydrangea. In general, if the hydrangea has large pink or blue flowers (Hydrangea macrophylla) it blooms on old wood (last year’s growth) and should be pruned after blooming. Smooth hydrangea (Hydrangea arborescens) and hardy hydrangea (Hydrangea paniculata) bloom on new wood.
If the hydrangea has conical flowers (even if they’re pink), large white blooms or green blooms, it should be pruned in early spring. Cut the stems back to about 2 feet. This will promote new growth and enable the shrub to support the huge, heavy flowers.
If you prune at the wrong time, don’t worry. The shrub or tree may not bloom for one season but will likely bounce back with blooms the next.
It is best not to prune trees in the fall. New growth is slower at this time of year so wounds take longer to heal, increasing the chance for disease.
Tree “topping,” the removal of the top of a tree to keep it shorter, is never a good idea. This results in unsightly, unhappy trees that will have weak branches that become a hazard.
If a tree or shrub is overgrown, remove 1/3 of the largest stems down to the ground and consider renovation or renewal pruning. More information on pruning can be found at the University of Minnesota Extension website: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/pruning-trees-shrubs/
Be sure to be safe and use the proper equipment when pruning.