Pruning Landscape Plants

"To prune or not to prune - that is the question!" It is a question which many anxious people consider each year at this time.

Proper pruning enhances the beauty of almost any landscape tree and shrub, while improper pruning can ruin or greatly reduce its landscape potential. In most cases, where landscape plants are concerned, it is better not to prune than to do it incorrectly. In nature, plants go years with little or no pruning, but man can ruin what nature has created. By using improper pruning methods healthy plants are often weakened or deformed.

In nature, every plant eventually is pruned in some manner. It may be a simple matter of low branches shaded by higher ones, resulting in the formation of a collar around the base of the branch, restricting the flow of moisture and nutrients. Eventually the leaves wither and die, and the branch will drop off during a high wind or storm. Often, tender new branches of small plants are broken or pulled off by wild animals in their quest for food. In the long run, a naturally growing plant assumes the shape that allows it to make the best use of light in a given location and climate. All you need to do to appreciate a plant's ability to adapt itself to a location is to walk into a wilderness and see the beauty of naturally growing plants.

More trees are killed or ruined each year from improper pruning than by pests. Remember that pruning is the removal or reduction of certain unnecessary plant parts—parts that are no longer effective or that are of no use to the plant. Pruning supplies additional energy for the development of flowers, fruits and limbs that remain on the plant. Pruning, which has several definitions, essentially involves removing plant parts to improve the health, landscape effect or value of the plant. Once the objectives are determined and a few basic principles are understood, pruning is primarily a matter of common sense.

The necessity for pruning can be reduced or eliminated by selecting the proper plant for the location at the outset. Plants that might grow too large for the site, are not entirely hardy, or become unsightly with age should be used wisely and kept to a minimum in the landscape plan. Advances in plant breeding and selection in the nursery industry provide a wide assortment of plants requiring little or no pruning. However, even the most suitable landscape plants often require some pruning.

Pruning should follow a definite plan. Consider the reason or purpose before cutting begins. By making the pruning cuts in a certain order, the total number of cuts is reduced greatly. The skilled pruner first removes all dead, broken, diseased or problem limbs by cutting them at the point of origin or back to a strong lateral branch or shoot. Often, removing this material opens the canopy sufficiently so that no further pruning is necessary.

The next step in pruning is to make any training cuts needed. By cutting back to lateral branches, the tree or shrub is trained to develop a desired shape, to fill in an open area caused by storm or wind damage, or to keep it in bounds to fit a given area. To properly train a plant, you should understand its natural growth habit. Always avoid destroying the natural shape or growth habit when pruning.

Make additional corrective pruning to eliminate weak or narrow crotches and remove the less desirable leader where double leaders occur. After these cuts have been made, stand back and take a look at your work. Are there any other corrective pruning cuts necessary? If a considerable amount of wood has been removed, further pruning may need to be delayed for a year or so.

To open up a woody plant, prune out some of the center growth and cut back terminals to the buds that point outward. In shortening a branch or twig, cut it back to a side branch and make the cut 1/2 inch above the bud. If the cut is too close to the bud, the bud usually dies. If the cut is too far from the bud, the wood above the bud usually dies, causing dead tips on the end of the branches. When the pruning cut is made, the bud or buds nearest to the cut are usually the new growing point. When a terminal is removed, the nearest side buds grow much more than they normally would, since apical dominance has been removed. The bud nearest the pruning cut becomes the new terminal. If more side branches are desired, remove the tips.

The strength and vigor of the new shoot is often directly proportional to the amount that the stem is pruned back since the roots are not reduced. For example, if the deciduous shrub is pruned to 1 foot from the ground, the new growth will be vigorous with few if any flowers the first year. However, if only the tips of the old growth are removed, most of the previous branches are still there and new growth is shorter and weaker. Flowers are more plentiful although smaller. Therefore, if a larger number of small flowers and fruits are desired, prune lightly. If fewer but higher quality blooms or fruits are wanted in succeeding years, prune extensively.

The height of a tree or shrub with 2 or more stems of equal size and vigor competing for dominance can be controlled by the length which they are cut back. A tree or shrub with 2 branches growing at the same height is commonly known as a split crotch, double leader or weak crotch. For a stronger plant that can better withstand ice and wind, cut 1 branch back or remove it completely. The remaining branch assumes apical dominance over other cutoff branches.

Thinning is a method of pruning usually recommended for most landscape trees. When thinning, remove an unwanted branch at its point of origin or at a strong lateral branch. This method conforms to the tree's natural branching habit and the results are less conspicuous. Thinning makes a more open tree and emphasizes the internal structure of the branches. Thinning also reduces breakage in wind and ice storms. Live oaks, in particular, need to be thinned out for this reason.

Unfortunately, dehorning, topping or heading is used too often to reduce tree size. While more rapid than thinning, the results usually are much less desirable. Re-growth is vigorous and upright from the stub. New branches form a broom?like growth arising from adventitious buds just below the surface and usually are weakly attached to the bark of the stubbed?back branch. Actually, it is a bunch of water sprouts weakly attached to the main trunk. Therefore, during wind or ice storms the branches break off easily.

Topping also shortens the life of trees, rendering them susceptible to insect and disease attacks. It also destroys the tree's natural shape. Do not prune the central leader of trees unless necessary. Over a period of several years, remove or cut back branches that compete with the leader if the branches are large. The crook that results at the base of a new leader seldom is noticeable after a few years.

For more information on pruning of ornamental trees and shrubs, see:
http://aggie-horticulture.tamu.edu/extension/pruning/PRUNING.html