Schmidt: When to Prune
Even though I do my best to offer annual horticulture and tree care workshops, it seems that with the arrival of spring a common question that arises is when should I prune my (insert common name) tree? Well, to answer the question, pruning is best done when trees are dormant about now is still OK but there are some exceptions such as birch, elm, maple and walnut which are prone to “bleeding” or leaking sap if pruned before they are fully leafed out. Also keep in mind that while spring is the best time to prune, the next best time is when you are in the mood or able to do it. The reason we recommend pruning in early spring before buds swell is because this enables the tree to naturally seal off pruning wounds most effectively and this time of year there are fewer pests to be attracted to and interfere with the healing of a pruning wound. Keep in mind that broken branches should be properly pruned as soon as they are noticed regardless of time of year. Don’t use pruning sealer, tar or paint on any tree cuts or wounds. A proper pruning cut doesn’t require sealer, and no amount of sealer can fix a bad pruning cut. One last bit of pruning advice to keep in mind is that proper pruning is essential in young trees to develop a tree with a strong structure and desirable form. Trees that receive the appropriate pruning measures while they are young will require less corrective pruning as they mature.
The following are pruning recommendations for some common species:
Ash: Anytime (early spring before leafing out is ideal)
Birch or Ironwood: To prevent bleeding, prune after fully leafed out.
Canada Red Cherry, Chokecherry, Hawthorns: For optimum flowering and fruiting, prune after flowering; otherwise prune before leafing.
Cottonwoods, Poplars, Aspen and Willows: Anytime (early spring before leafing is ideal).
Elm: To prevent bleeding, prune after fully leafed out.
Flowering Crab, Mountain Ash and Ornamental Pears: Before tree leafs out in spring.
Maples including Boxelder: To prevent bleeding, prune after fully leafed out.
Oaks: Anytime (early spring before leafing out is ideal).
Ohio Buckeye: Anytime (early spring before leafing out is ideal).
Russian Olive: Early spring before leafing out.
Tree Lilac: For optimum flowering, prune after flowering; otherwise prune before leafing out.
Walnut & Butternut: To prevent bleeding, prune after fully leafed out.
Renewal Pruning: Once shrubs get about five years old, they will benefit from renewal pruning. You can remove the oldest, thickest stems each year, cutting at ground level.
New Shrubs: Young shrubs need very little pruning. Only remove dead wood, broken branches, and branches that rub against one another. After about five years, shrubs are well-established and require regular pruning.
Spring Bloomers: Lilacs, forsythia and other spring flowering shrubs are now loaded with flower buds. You can prune them now, but you will be reducing your spring bloom. Most gardeners wait to prune these shrubs immediately after they are done blooming. Follow the same techniques described above under renewal pruning.
Overground Shrubs: Sometimes it’s best to prune badly overgrown shrubs down to the ground. This can be done for neglected forsythia, Annabelle hydrangea, honeysuckle, potentilla, privet and pink-flower spireas. These plants will establish new growth quickly. Severe pruning is best done during the dormant season.
Evergreen Shrubs: Evergreen branches can be removed during the dormant season. Light trimming is best done after new growth begins in April or around the Fourth of July.
Arborvitae, Junipers, Yews: Late spring to late summer (not after August 15).
Pine: After new growth has elongated but before it forms a new bud is the best time.
Spruce: Just before buds open or just after new growth is fully extended is the best time.
For more information and instructions on making proper pruning cuts check NDSU publication H1036- “Basic Guidelines for Pruning Trees and Shrubs” which can be found online at www.ag.ndsu.edu/pubs/plantsci/trees/h1036.pdf or the International Society of Arboriculture’s publication “Pruning Young Trees” which can also be found online at www.treesaregood.com/treecare/resources/pruning_youngtrees.pdf .
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