How to Prune A Tree
Large trees aside, there are many pruning jobs that you can do on your own. In all cases, the key is to prune the unwanted branch while protecting the stem or trunk wood of the tree. Tree branches grow from stems at nodes and pruning always takes place on the branch side of a stem-branch node. Branches and stems are separated by a lip of tissue called a stem collar which grows out from the stem at the base of the branch. All pruning cuts should be made on the branch side of this stem collar. This protects the stem and the other branches that might be growing from it. It also allows the tree to heal more effectively after the prune. To prevent tearing of the bark and stem wood, particularly in the case of larger branches, use the following procedure:
1. Make a small wedge shaped cut on the underside of the branch just on the branch side of the stem collar. This will break the bark at that point and prevent a tear from running along the bark and stem tissue.
2. Somewhat farther along the branch, starting at the top of the branch, cut all the way through the branch leaving a stub end.
3. Finally, make a third cut parallel to and just on the branch side of the of the stem collar to reduce the length of the stub as much as possible.
A similar procedure is used in pruning one of two branches (or one large branch and a stem) joined together in a 'u' or 'v' crotch. This is known as a drop crotch cut. Make the first notch cut on the underside of the branch you're pruning well up from the crotch. For the second cut, cut completely through the branch from inside the crotch well up from the ridge of bark joining the two branches. Finally, to shorten the remaining stub, make the third cut just to one side of the branch bark ridge and roughly parallel to it.
When To Prune A Tree
The dormant season, late fall or winter, is the best time to prune although dead branches can and should be removed at any time. Pruning during the dormant period minimizes sap loss and subsequent stress to the tree. It also minimizes the risk of fungus infection or insect infestation as both fungi and insects are likely to be in dormancy at the same time as the tree. Finally, in the case of deciduous trees, pruning when the leaves are off will give you a better idea of how your pruning will affect the shape of the tree.
How Much To Prune
When deciding how much to prune a tree, as little as possible is often the best rule of thumb. All prunes place stress on a tree and increase its vulnerability to disease and insects. On no account, prune more than 25% of the crown and ensure that living branches compose at least 2/3 of the height of the tree. Pruning more risks fatally damaging your tree. In some cases such as storm damage, height reduction to avoid crowding utility lines, or even raising the crown to meet municipal bylaws, your pruning choices are made for you. But even in these instances, prune as little as possible.
Determining the Need for Fertilization
Trees in urban and suburban environments are often under high stress conditions due to low moisture availability, soil compaction, physical damage, nearby construction, and competition from turf and nearby trees and shrubs. Fertilizer applications may reduce, but cannot eliminate, environmental stresses such as these. It is important to keep newly planted trees watered and pruned and to keep weeds away from their bases to avoid excess stress.
The best indicator of whether fertilization is necessary is a soil test. Ideally, a soil sample should be taken before trees are planted. Additional samples can be taken every 3 to 5 years thereafter to determine whether any nutrients are lacking. A soil test kit may be obtained from your county extension service.
In the absence of a soil test, the best indicator of the need for additional fertilization of established trees is shoot growth. If new shoot growth (growth occurring in the present year) is in excess of 6 inches, then fertilization is probably unnecessary. If shoot growth is between 2 and 6 inches then fertilizer may be applied and, if shoot growth is under 2 inches, then fertilizer applications are appropriate as indicated in the Application Methods and Rates section.
Foliage color is another indicator of the need for fertilization. Yellow or “off-color” leaves may indicate the need for fertilization as these symptoms generally occur on trees which are not taking up enough of one or more required nutrient. Always remember, however, that apparently “off-color” leaves are normal for certain plants such as ‘Sunburst’ Honeylocust and some maple and ash trees in the fall.
A final indicator of the need for fertilization is the history of the yard. Trees in yards that are fertilized for turf on a regular basis rarely need to have supplemental fertilizer applied. Supplemental fertilizer should only be considered if shoot growth is less than 2 inches, or if a soil test reveals a specific nutrient deficiency.
When to Fertilize
Most trees experience a single flush of growth during spring followed by slower growth throughout the summer and fall. Because of this single flush of growth, it is desirable to have nutrients available to the tree as this growth is about to occur. The most beneficial time to apply fertilizer is from when the ground is workable in the spring until just before trees start growing in early May. On sandy soils, applications should be split, half in early spring and half in mid- to late May.
If a tree shows yellowing, extremely slow growth, or some other sign which might indicate a nutrient deficiency, then fertilizer can be applied at any time during the growing season. If fertilizer must be applied under the hot, dry conditions of the summer, it is important to provide water for the tree soon after fertilizer is applied so that salts from the fertilizer don’t build up and damage the tree’s root system. Two to three inches of water (as measured by a rain gauge) applied every two or three weeks around the area where fertilizer was applied will be sufficient to wet the top 1-1 ½ feet of most soils. Sandier soils will require lighter, more frequent watering while clay-based soils will require heavier watering less frequently.
What to Apply
Unless a tree is deficient in some other element, increased nitrogen provides the most pronounced effects on the growth of all plant nutrients. Just because an increase in nitrogen produces a more visible increase in growth, however, does not mean that other elements are not required. A soil test provides the best indicator of elements that may need to be added to the soil to prevent nutrient problems. High rates of P fertilizer should not be used unless a need is indicated by a soil test. If soil test P is high then it is best to use fertilizers such as 24-0-15, 30-0-10, 32-3-10, 18-5-9, 27-3-3, or 16-4-8 with a high rate of N and a low or zero rate of P. High rates of P can negatively affect the environment by causing excessive algae to grow in nearby lakes and streams which will, in time, kill fish and other aquatic life. Never use a fertilizer which includes any kind of herbicide around a tree. These fertilizers may be beneficial to turf, but can damage trees.
Application Methods and Rates
Landscape plants typically go through 3 stages of nitrogen need: a) newly planted stage, 1-2 years after planting; b) young rapid growth stage; 3-5 years after planting; and c) mature, maintenance stage, 5 or more years after planting. Nitrogen needs should be adjusted to account for the stage of growth. For full details on how to apply fertilizer based on nitrogen need stage, please visit: http://www.extension.umn.edu/distribution/horticulture/dg7410.html