Pointers for pruners

Last Updated: 
February 5, 2008

ROSEBURG, Ore. – Pruning woody landscape plants is daunting to many property owners, who may wonder if all plants should be pruned alike.

People who are unsure of what to do tend to approach pruning only as a size control process, according to Steve Renquist, a horticulturist with the Oregon State University Extension Service. Renquist has advice to those who feel baffled by pruning the woody ornamentals in their yard.

"Pruning is both art and science and not something most of us get training in," said Renquist. "Pruning should both enhance a plant's natural beauty and form, and keep the plant vigorous and productive whether it is a flowering tree, shrub, or a fruit tree."

When working with shrubs Renquist offers a couple of rules to follow to get started on good pruning practices.

First, learn the two types of cuts used on shrubs – heading cuts that remove ends of branches to make the plant denser and thinning cuts that remove entire branches or canes to give the plant a more open form.

Second, learn what the natural shape or habit is for each shrub in your landscape. There is good information in gardening books, including those published by Sunset and others.

Mound-forming shrubs, such as Abelia or Escallionia, need thinning cuts near the ground level. Remove tall shoots that tower above the mound form. Don't shear mound-forming shrubs or they will become too dense.

Cane forming shrubs, including Forsythia and lilac, should be allowed to reach their natural height. Then, every year, use thinning cuts and take out one-eighth to one-fifth of the canes, preferably the oldest.

Upright or tree-like shrubs, like rhododendrons or Pieris, usually need little pruning and will look best when thinned slightly every few years. Save heading cuts for hedges, where tight compact growth is desirable.

Flowering shrubs and trees require a little more thought before pruning if you want them to bloom nicely each year. Most importantly, consider when these plants bloom; if they bloom in late winter or spring you want to prune after bloom. If they bloom in summer or fall you want to prune during dormancy in winter.

Never cut the top out of a tree. Topping destroys a tree's natural beauty and weakens it structurally. When planting trees, plan ahead and put them in a location that matches their natural height. That way, they won't need topping when they reach your eave or power line.

Think before you plant a new tree, advised Renquist. Shade trees need open sky and plenty of distance from a home to avoid damage by falling or dropping limbs. Small flowering trees fit under power lines or close to a structure.

If you have to reduce the height of a tree, use a thinning cut to remove the tallest limbs in their entirety. If an old tree is causing you some concern, you can take weight off without topping in this manner.

To learn more about pruning ornamentals, shade trees, or fruit trees plan to attend one of the many pruning classes offered by OSU Extension and the Master Gardeners in January, February, and March. Contact your local county OSU Extension office for more details.

Author: Carol Savonen
Source: Stephen Renquist