April 10, 2021 - Pruning Basics
Here at Extension Brown County, we receive many questions throughout the year related to pruning trees, shrubs and evergreens. Proper pruning can be of real benefit to your plants, but improperly done can cause injury to plants! First, you need to ask yourself what you hope to accomplish through pruning and then understand proper techniques and the best timing for the job.
Why? – Pruning is often conducted to remove dead and diseased branches, to control shape and size, to stimulate flowering/fruiting, to rejuvenate older and out of proportion plants, to open canopies to increase airflow to reduce diseases, eliminate double leaders and develop strong scaffold branches. Pruning is especially an essential practice for young trees to create strong trunks and branching structure that will benefit the tree as it matures.
When? – Timing is very important but can vary depending on whether you are trimming evergreens, deciduous trees (those that lose their leaves in fall), or shrubs.
For the most part, the best time to prune deciduous trees is in late winter/early spring while the tree is dormant. This makes sense since insects and disease organisms are not active, you can easily see the branch structure to determine where cuts are needed, and the tree will be able to vigorously seal over the wound with what is called callus tissue in spring. FYI -Trees do not “heal” wounds, they “seal” them over with this tissue. You want this sealing to occur as fast as possible to prevent disease and insect damage at the wound site. This process is best done by the tree alone without the use of a wound dressing (like the black tree paint that was used years ago). Remember that there are pruning times for oaks set by the municipality to prevent the spread of oak wilt disease. In Bellevue, the pruning window is from September 1 to April 1. If an oak must be pruned during the growing season because of wind damage, etc. then wound paint would be applied to keep out the insect responsible for spreading the disease.
Evergreens can be a bit tricky when it comes to pruning. Some species do not need much pruning at all, but you may want to control size/shape on other types and timing may vary according to the species. Do your research to determine the best time!
To figure out the appropriate time to shape your shrubs, consider the bloom period. If a shrub blooms in summer (roses, potentilla, Japanese spirea, etc.), then prune it when dormant during the late winter/early spring. These shrubs flower on this year’s branch growth, so you will not be cutting off flower buds (if pruned early enough). But spring blooming shrubs (lilacs, weigela, forsythia, etc.) should be pruned right after blooms fade to preserve the flower buds that will grow and bloom next spring. It will not actually hurt the shrub to prune at a different time, but you may not have as many flowers next spring!
How? – Pruning is much more than hacking off a branch at some point along its length! There are many types of pruning cuts, but in most cases, you will be cutting off a branch at the trunk of the tree to raise the height of the branches so you can mow under them, etc., to eliminate a double leader situation or you may want to thin out your tree canopy for better light penetration and air flow by cutting smaller branches back to a larger branch at their point of origin. These cuts need to be done properly so that the tree can seal itself as quickly as possible. Leaving a six-inch stub sticking off the trunk is not a proper pruning cut! There is a science to the pruning techniques so do your homework!
There are many good resources on pruning that can be found on the internet at research-based educational sites (websites ending in .edu or .gov). UW-Madison Division of Extension has several good pruning guides that can be found at The Learning Store (learningstore.extension.wisc.edu) including fact sheets on pruning deciduous trees, evergreens and shrubs. The Horticulture Help Desk at Extension Brown County is also a great resource for this and other landscape-related topics and can be contacted by calling 920-391-4615 or emailing firstname.lastname@example.org.
Source: UW-Madison Division of Extension (learningstore.extension.wisc.edu) Publications: Pruning Deciduous Shrubs (XHT-1015), Pruning Evergreens (XHT-1013) and Pruning Deciduous Trees (XHT 1014)
Written by: Doug Hartman, Extension Brown County Horticulture Assistant