Time to Prune Trees
Iowa State University Extension
Oskaloosa, Iowa – The Mahaska County Extension Office recently received a notice from the City of Oskaloosa concerning the trees on their property that have low hanging limbs in the city right of way. Many other Oskaloosa landowners may have received this notice.
The trees on the Extension Office property were planted roughly ten years ago by Oskaloosa Trees Forever. Many trees were planted by Trees Forever at that time and may need pruning. Many landowners may have additional trees which need pruned. These landowners maybe unsure of how to prune their trees. Proper pruning includes knowing which branches to remove, when to do it, and how to minimize damage to the tree.
When done properly, pruning can improve the health and structure of trees, and provide a safer environment for all. There are many sources of information on proper tree pruning. Iowa State University Extension and Outreach is one source. The following information is included on the ISUEO Forestry Extension website. http://www.extension.iastate.edu/forestry/care_maintenance/pruning.html. More information on all aspects of tree care can be found in additional publications available at this website, ISUEO horticulture publications and our office. Many ISUEO publications are available at https://store.extension.iastate.edu.
The main reason to prune young trees is to develop good branch structure and tree strength. Removing weak branches and correcting poor form when branches are small, will minimize the size of the pruning wounds. Early pruning will also promote strength and balance that will make a tree less susceptible to damage from wind, ice, and snow storms.
If your tree is near electrical lines or tall enough that you must climb the tree to prune it, your pruning task is best left to qualified professionals. Also, acknowledge your own limitations, if it is one you cannot safely perform, it is best to hire it done.
The best time to prune is in mid to late winter (January-March). When pruned during this time of the year, the tree will begin responding to the wounding early in the spring. A coniferous tree planted in a suitable site, will need minimal pruning throughout its life.
Pruning at other times of the year will not hurt a tree; however the process of sealing the wound may be slowed. Do not prune during the spring from bud break through leaf expansion, and during the period of leaf color change in the fall. A tree is going through major changes at these times, and branch removal can reduce the vigor of a tree.
Oak is exception, with this species where timing of pruning is critical. The pathogen that causes the disease Oak Wilt can be transmitted to open wounds by a small beetle. To avoid, do not prune oak trees between early March until late July.
Limit the pruning of newly planted trees to the removal of dead and broken branches or the correction of multiple leaders. Begin developmental pruning of deciduous trees 2-3 years after planting. Key things to remember when pruning trees are:
Know the general growth habit of a tree before beginning.
Leave the temporary lower branches on the tree until they reach 1 inch in diameter to increase trunk growth and root development.
Always leave 70 percent of the tree height with live branches.
Avoid removing lower branches too quickly, keeping lower branches longer allows for larger and stronger tree trunks
Concentrate efforts on removing crossing, rubbing, broken, diseased and weak-angled branches in the upper portion of the tree.
Eliminate double leaders and basal sprouts.
Space permanent branches 15-35 inches apart.
Remember developmental pruning is an on-going process over the first 15-20 years of a tree’s life.
Before deciding which branches to remove, always examine the tree carefully. Before making a pruning cut, identify the branch bark ridge and branch collar. The branch bark ridge is where the branch and trunk tissue meet. The branch collar is the swollen area just outside the branch bark ridge
Do not cut behind the collar and branch bark ridge creating a “flush cut”. Removal of these two structures impedes the tree’s ability to respond to the wound, which increases the chances of decay development.
Do not leave a stub.
Do not top a tree, which is the removal of branches without regard to the location of lateral branches or buds
Always remove branches back to their point of origin or to a side branch of sufficient size to assume dominance.
The best indicator of proper pruning is the development of wound closure tissue on the tree. Usually within a year, a ring (donut-shaped) of callus tissue will begin to develop around the existing wound.
A number of studies have shown the use of wound dressings or paints do not speed up the tree’s ability to seal a wound. In most cases, pruning paints create a favorable environment for decay causing organisms. At this time, pruning paints are no longer recommended.
In Oskaloosa, debris from yard work including tree pruning may be taken to the Tree dump (city lot at the intersection of Suffolk Road and Third Ave West). Please leave only organic debris at the tree dump.
