This past week in the Gardening for Fun and Profit Class we talked about and demonstrated the myriad of gardening tools available to the home gardener. Some of the tools are used in pruning trees and shrubs and I thought it would be good to write about pruning and some of the tools that are used in this activity.
Pruning is a regular part of plant maintenance involving the selective removal of specific plant parts. Although shoots and branches are the main targets for removal, roots, flower buds, fruits and seedpods may also be pruned.
Pruning wounds plants, but plants respond by covering damaged areas with callus tissue. Chemical boundaries form around wounded areas, walling off or compartmentalizing the wounds. This limits any decay that results from wounding or from the natural death of branches. Use pruning techniques that minimize plant wounding and speed closure.
The recommendations have changed on pruning and current recommendations advise against pruning branches flush to the trunk. Flush cutting is harmful in several ways: It damages bark as pruning tools rub against the trunk, it removes the branch collar and goes behind the branch bark ridge.
The branch collar is the swollen area of trunk tissue that forms around the base of a branch. If you prune away the branch collar, you remove not only branch wood, but also trunk wood, which opens the plant to more extensive decay. The branch-bark ridge on trees is a line of rough bark running from the branch-trunk crotch into the trunk bark. It is less prominent on some trees than on others. The best pruning cut is made outside the branch collar, at a 45 to 60 degree angle to the branch bark ridge.
So, why should you prune your trees or shrubs?
▪ To improve the appearance or health of a plant. Prompt removal of diseased, damaged or dead plant parts speeds the formation of callus tissue and sometimes limits the spread of insects and disease. For trees, pruning a dense canopy permits better air circulation and sunlight penetration. To avoid future problems, remove crossing branches that rub or interfere with each other and those that form narrow crotches.
▪ To control the size of a plant. Pruning reduces the size of a plant so that it remains in better proportion with your landscape. Pruning can also decrease shade, prevent interference with utility lines and allow better access for pest control.
▪ To prevent personal injury or property damage. Remove dead or hazardously low limbs to make underlying areas safer. Corrective pruning also reduces wind resistance in trees. Prune shrubs with thorny branches back from walkways and other well-traveled areas. I would suggest to have trained or certified arborists handle any pruning work in the crowns of large trees. The older I get, the less excited I am about working with large trees, especially the dead ash trees that are a result of the Emerald Ash Borer — of which I have many — that will be used for lumber and firewood.
▪ To train young plants. Train main scaffold branches (those that form the structure of the canopy) to produce stronger and more vigorous trees. You’ll find it easier to shape branches with hand pruners when a plant is young than to prune larger branches later. Pruning often begins with young plants for bonsai, topiary, espalier or other types of special plant training.
▪ To influence fruiting and flowering. Proper pruning of flower buds encourages early vegetative growth. You can also use selective pruning to stimulate flowering in some species, and to help produce larger (though fewer) fruits in others.
▪ To rejuvenate old trees and shrubs. As trees and shrubs mature, their forms may become unattractive. Pruning can restore vigor and enhance the appearance of these plants.
The next column will discuss some of the pruning tools used to accomplish these goals.
Bill Lamont is a professor and extension vegetable specialist in the department of plant science at Penn State and can be reached by email at email@example.com.