This article was originally published in Colorado Patio & Landscape.
Arborists are often asked or required to trim or prune landscape trees throughout the year. Sometimes it’s because a tree has been damaged by a storm, while in other cases it may be at the request of a homeowner or commercial property manager. While we can’t always determine when a tree will be pruned, late winter is the ideal time of year to make major structural changes to most tree species.
February through early March is best for pruning landscape trees because they are still dormant. Also, unlike in fall or early winter, wound closure will be rapid if pruning occurs just prior to the time new growth emerges.
Pruning trees later in the dormant season reduces impacts on tree health, and builds a strong structure for our community trees in the long term. Although some elms, maples, birch and walnut trees may visibly exude sap if pruned in the late winter or early spring, you can assure clients that this should not harm the tree.
Here are several tips to consider whenever pruning trees:
- Know exactly what you want to accomplish before you saw. Don’t remove any branches without a reason.
- Remove any torn, dead or broken branches.
- Try to develop or maintain one dominant vertical top stem, or leader, for most species, and don’t cut off the tops of trees.
- Space the main branches along the trunk, and prevent branches below the permanent canopy from growing upright or too large.
- Always prune just outside the branch collar – the point where one branch leaves a larger one (or the trunk), often discerned by raised or wrinkled bark.
- Limit pruning of newly planted trees to the removal of dead, damaged or crossing limbs, or those interfering with the main stem.
- Avoid removing more than 25% of a tree’s branches in any one year.
Also avoid transporting material from hardwood tree species over any significant distance—especially ash wood. Due to the growing problem of emerald ash borer (EAB) in Colorado, a quarantine currently exists that prevents the removal of any hardwood firewood or logs from Boulder County.
Be sure to wear the proper protective equipment when pruning, especially for any job that requires you to run a chainsaw. If a chipper is being used to address removed wood, always be sure to go over the proper safety and shut-off procedures with your crew prior to starting work.
Remember that many communities in Colorado have a licensing requirement for anyone doing tree work within their legal boundaries. Contact the communities where you do the majority of your work to ensure compliance. If you are not a licensed arborist, and do not have one working for your business, a list of professionals for jobs requiring a licensed, insured, certified arborist can be found at isa-arbor.com.
Keith Wood is the urban and community forestry manager for the Colorado State Forest Service, and the executive administrator of the Colorado Tree Coalition. He also teaches an urban and community forestry course at Colorado State University in Fort Collins. Keith has been a Certified Arborist since 1995 and a Certified Forester since 2002, and has worked in the forestry profession in Colorado for almost three decades.