Trees and shrubs are long-lived, important landscape plants and are a good investment for any property. They provide structure, borders and privacy, and increase property value.
They sequester carbon by absorbing carbon dioxide (a greenhouse gas) and holding it in their tissues. The branches, stems, and even leaves deflect and reduce the impact of heavy rains on soils, reducing run-off. Trees and shrubs improve energy efficiency when planted due west of west-facing windows and as windbreaks.
Trees and shrubs provide habitat and food resources for many important insects, birds, pollinators, bats and other animals. They also beautify our landscapes, provide refuge from the hot summer sun and cool the ambient temperatures around us.
Proper care and maintenance of trees and shrubs starts when they are planted in the ground, including pruning. Regular pruning of young and middle-aged trees and shrubs is crucial to the development of healthy and attractive plants. Regular pruning also improves plant form, promotes active growth, and protects people and property from trees that may present a higher risk. Make it a goal to prune trees and shrubs annually.
For more difficult pruning jobs, contact a certified arborist. These professionals have the skills and knowledge to advise on the health and to prune trees and shrubs correctly.
Late winter is a good time to prune many trees and shrubs in Minnesota. The plants are still dormant, so it is easier to observe the form of the plant and to make pruning decisions.
In all cases, clean and disinfect your pruning tools between cuts to avoid spreading disease between trees.
Trees
Some trees are susceptible to certain diseases and physiological problems. Pruning in late winter, right before spring growth starts, minimizes the length of time fresh wounds are exposed before the tree starts active growth and seals the wound.
Prune oaks from November through March. Oak wilt is a fungal disease that is lethal to red and white oaks. It is spread by two species of sap beetles that carry the fungus from tree to tree. Oak wilt can also spread via root grafts.
Do not prune oak trees from April through October. Wait to prune oaks in the winter. This oak wilt degree-day model estimates cumulative emergence of the two most important insects that transmit oak wilt (Colopterus truncatus and Carpophilus sayi) in the spring.
Pagoda dogwood in Minnesota may have golden canker, a fungal disease that causes yellow cankers to grow, girdle, and ultimately may kill the branches. Like oaks, prune pagoda dogwood in winter to reduce the potential for the disease to spread.
Prune honey locust trees in winter while still dormant to avoid stem cankers and Nectria canker.
Prune apples, flowering crabapple, mountain ash, hawthorn, serviceberry, and cotoneaster in late winter (February through April) to reduce the spread of fire blight, a bacterial disease that can infect susceptible trees and shrubs through wounds.
Late spring pruning
Some trees will “bleed” sap if pruned in later winter. While this doesn't hurt the tree, it can concern tree owners. To avoid this, wait to prune the following trees in late spring or early summer after leaves have fully expanded.
- Maples
- Butternut
- Black walnut
- Ironwood
- Beech
Although birch trees also bleed sap when pruned in late winter, this timing is preferable because it helps avoid attracting bronze birch borers, which are active during the growing season. The borer is attracted to wounding on trees, especially stressed trees. It girdles susceptible birch trees, blocking the vessels that move water and nutrients through the trees.
Shrubs
Shrubs grown primarily for their foliage or bloom in summer should be pruned in late winter or early spring before they start actively putting on new spring growth. Deadhead or remove a third of older branches to encourage blooming and new, more attractive growth. Remove winter dieback and take this opportunity to improve the form of your shrubs by removing uneven branches.
- Alpine currant
- Arrowwood viburnum
- Buffaloberry
- Burning bush
- Butterfly bush
- Buttonbush
- Dogwood
- Honeysuckle
- Hydrangea - panicle, smooth and bigleaf
- Kalm St. John’s Wort
- Magnolia
- Northern bush honeysuckle
- Peashrub
- Roses (repeat bloom varieties)
- Smokebush
- Sweet shrub
- Sumac
- Summer-blooming spirea