Pruning Principles

Plant owners frequently rely on pruning to solve a variety of design problems on their property. Basically, they resort to pruning to control plant size in the landscape. If you find that pruning is needed every season to keep a specific plant within pre-determined bounds you should give considerable thought to removing the plant and replacing it with another genus or species that has growth characteristics better suited to the site limitations. Such severely pruned plants are generally not all that attractive in the landscape and require far too much maintenance time to justify the quality of the end product.

With few exceptions, most plants in the landscape should require light or moderate pruning every few years at most. Without it, many plants tend to decline long before they reach their potential as a landscape specimen. Pruning will maintain a constant supply of younger, more productive flowering wood on most plants. Most individuals can easily care for their plants once they understand what constitutes proper pruning and when their plants should be pruned.

To most individuals there is little difference between the practice of shearing and pruning; both techniques result in the removal of unwanted plant growth. However, the final appearance of the plants will be directly related to the technique used to care for the plants. The major difference between pruning and shearing is that pruning involves the individual cutting of each branch or twig that you wish to remove. Shearing is the indiscriminate clipping of all twig ends on the plant.

Any pruning will stimulate new growth and branching from a point immediately below the cut. Pruning will alter the chemical nature of the plant because it removes growth chemicals contained in the terminal bud. While these chemicals are present, they restrict the elongation and growth of lateral buds below that point on the stem. Once this dominant chemical is removed through pruning some plants have a greater ability to generate new growth from lateral buds or dormant buds inside the stem.

Pruning takes off larger pieces of growth at specific locations on the plant and only affects the dominance on individual stems that have been cut. Shearing on the other hand generally removes one to two inches of growth from all the stems over the entire surface of the plant. The shearing destroys the dominance on all stems and produces excessive growth and branching. Pruning will be effective in reducing the overall density and height of most plants, while shearing will also control size, but tends to increase surface density of the foliage and internal shading of future growth.

Before you begin pruning or any form of cutting on plants it is important to consider what you are attempting to accomplish with the operation. You should also consider the properties of the individual plant: its natural form, habit of growth, rate of growth, height, spread, and time of flowering. After considering all these factors, you can begin pruning. For example, a fast-growing plant might be pruned harder than a slow-growing one. If flowers are of value you will want to prune after the flowering period.

Generally plants that are pruned can go longer without subsequent attention and retain their quality longer than plants that are sheared. It is very important to realize that a properly pruned plant should not show any definite signs of cutting.

**Dr. Robert Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor’s, master’s, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.