Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
2/8/99
Contacts:
Mark Vitosh, Extension Forestry, (515) 294-6739
Elaine Edwards, Extension Communication Systems, (515)
294-5168
Yard and Garden Column for the Week Beginning Feb. 12
It's Cold! Get Out and Prune Those Shade Trees
by Mark Vitosh
Extension forester
Iowa State University
Are you tired of being stuck inside this winter? Well, a great way to burn off some of your stored energy is to get outside and check to see if the trees that you have planted within the last few years need pruning. Pruning, in the winter? Yes, this is not a typo. Pruning when the leaves are gone on deciduous trees will make it easier to see the tree's structure and allow you to remove the appropriate branches. Just a second now, before you get out there and start slinging branches in the backyard, we should talk a little about pruning.
Pruning is more than just going out and randomly removing branches. Proper pruning includes understanding the reasons for removing branches, which branches to remove, when to remove them and how to minimize damage to the tree.
Why prune young trees?
The main reason to prune young trees is to develop good branch structure and strength that will make the tree less susceptible to damage from wind, ice and snow storms. There have been a number of storms that have caused great damage to trees across Iowa in the last two years, and some of the damage could have been avoided with proper and timely pruning when the trees were younger. Pruning young trees can remove dead, diseased and dying branches to improve tree health and create clearance between lower branches and the surroundings. Also, wounding to the tree can be minimized by pruning when branches are smaller (less than 2 inches in diameter).
When do you start pruning a new tree?
It is a common practice to remove the first couple feet of lower branches of a newly planted tree as soon as possible to allow clearance for mowing equipment. This practice can have a negative impact on the development of a young tree. A newly planted tree goes through transplant-related shock, and the removal of live branches immediately after this time can reduce the tree's food-making capabilities.
When trees are planted all they need the first two years is a layer of mulch around their base to protect them from the lawnmower and weed whipper, and timely waterings to promote establishment. Pruning immediately after a new tree has been planted should be limited to removing dead and broken branches, and double leaders to maintain one single main stem. Most coniferous species (e.g. pine, spruce and fir) that are planted in suitable sites will need minimal pruning beyond the development of a single stem. Developmental pruning of deciduous trees should begin two to fours years after the trees have been planted or when lateral branches are between 1 to 2 inches in diameter, and it should continue until the trees are mature.
Which branches should be removed?
Growing a strong well-developed tree does not happen overnight. Below are a few factors to consider as you begin to prune younger shade trees.
* Concentrate pruning efforts on removing crossing, rubbing, broken, diseased and narrow-angled branches and double leaders in the upper portion of the tree.
* Always leave 70 to 75 percent of the tree height with live branches. Avoid removing lower branches too quickly.
* Leave the temporary lower branches on the tree until they reach 1 inch in diameter to increase trunk growth and root development, and then remove them before they reach 2 inches in diameter to minimize the size of wound.
* On low-growing species such as crabapple that do not have a main trunk, concentrate efforts on removing broken, weak-angled, rubbing and competing branches. Also, consider removing sucker sprouts along branches and at the base of the trunk.
What time of year should you prune?
Dead branches can be removed at any time, but when pruning live branches of both deciduous and coniferous species, certain times of the year are better than others. The pruning time that is favorable to most trees is mid-winter (January to March) before the buds begin to open in the spring. During this time of the year insect and disease-causing pathogens are at low levels, and the tree will begin responding to the wounding early in the spring.
Avoid pruning during the spring from bud break through leaf expansion, and during the period of leaf color change and leaf drop during the fall. Trees are going through major changes at these times and branch removal can weaken the tree during these periods. One species where the timing of pruning is critical is oak. Avoid wounding (pruning) oaks from the start of March until the end of July to help prevent the spread of Oak Wilt disease.
How do you make a pruning cut?
Before deciding which branches to remove, always take a step back and examine the tree carefully. Before removing a branch, identify the branch bark ridge and branch collar. The branch bark ridge is where the branch and trunk tissue meet. This area is usually indicated by a ridge of bark between a branch and the trunk. The branch collar is the swollen area just outside the branch bark ridge. When removing a branch, use the following recommendations to promote proper tree response:
* To avoid bark tearing, remove the weight of the branch before making the final cut just outside the branch collar.
* 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 in the tree.
* Do not leave a stub.
* Do not top a tree, which is the indiscriminate 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 which is at least one-third as large as the branch being removed.
* Pruning paints or wound dressings are no longer recommended.
The best indicator of proper pruning is the development of wound closure tissue on the tree. Usually within a year after branch removal, a ring (donut-shaped) of callus tissue will begin to develop around the wound of a properly pruned branch. Now you know some of the basics of pruning young trees, it is time to take a look at your own trees.
Before you head outside to start pruning, dress warm, put on your safety glasses (little pieces of wood in the eye are not fun), put on your working gloves (helps avoid pruning cuts to your fingers), leave the can of pruning paint in the garage (use it on the dog house next summer instead) and remember developing strong and healthy young trees is accomplished over a number of years and not all in just one afternoon. More information on proper pruning and care of young trees can be found in Iowa State University Extension pamphlet, "Community Tree Planting and Care Guide" (Pm-1591), which is available at your county extension office.
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