When to Prune

By: Jennifer LaMontagne – Horticulturist – Bloch’s Farm – Green Lake, WI

            Pruning and the removal of dead limbs is an important part of annual tree and shrub maintenance. It supports the overall health of trees and shrubs and improves their appearance. Properly timed pruning encourages trees and shrubs to rebloom and increases their flower and fruit outputs.  

It can be confusing as to the proper timing of pruning different trees and shrubs. One helpful tip is to note whether they flower on new wood or old wood. Trees and shrubs that bloom on new wood often begin flowering mid- to late summer. The best time to prune them is during late winter or early spring, when they are dormant, and no new growth has yet appeared. This will provide them time to recover and an opportunity to put all their energy toward producing new growth and buds.

Arborvitae, for example, do well when pruned in spring just before new growth is produced.  New growth will develop in the crotch of the branches and will cover the pruning cuts. February to early April is the best time to prune apple trees, crabapples, mountain ash, and hawthorn to prevent chances of infection and the spread of bacterial diseases. It’s best to prune shade trees in late winter or early spring, and to decrease the chances of oak wilt disease, it’s a good rule of thumb to prune oak trees before mid-April. 

Certain trees such as elm, maple, birch, and black walnut may ooze sap if cut back in the spring. This does not harm the tree; however, these trees can also be pruned in early summer or late fall to reduce oozing if it’s concerning to you.

Boxwoods and other evergreen or ornamental shrubs such as butterfly bush, sumac, and red-twig dogwood typically benefit from an annual spring trim to keep their shape and to support their good health. Panicle and smooth hydrangeas, burning bush, roses, rose of sharon, coralberry, potentilla, diervilla, honeysuckle are other varieties of shrubs that flower on new wood.

However, not all trees and shrubs should be pruned in spring. Those that bloom in early summer on mature, or old wood should typically be pruned in late summer or early fall before the next season’s buds begin forming. If you prune them in spring, you will be removing the flower buds. It’s best to wait until right after they have finished flowering. This will provide a time for beautiful blossoms and a time for new buds to develop.

Dogwood trees, as opposed to the red-twig dogwood bush, are an example of a tree that should not be pruned in spring due to an increased chance of harmful insects boring into the cut areas. It also seeps a very sticky sap if pruned during its active growth period, so it’s best to hold off on any needed pruning until late fall or winter. Other flowering trees such as cherry, pear and magnolia can be pruned when their blooms have faded away.  

Lilac bushes need to be pruned soon after their flowers are spent. Like other bushes that bloom on mature wood, lilacs set the buds for next season almost immediately after the last blossom has faded. Other examples of shrubs that bloom on old wood are bigleaf hydrangea, forsythia, weigela, and azalea.

Bloch’s Farm will be open soon! We are currently busy getting ready for all your spring needs. Call 920-294-6000 or e-mail jlamontagne@blochsfarm.com with any questions. You can also check out our website online at www.blochsfarm.com and follow us on Facebook and Instagram.

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