Schedule Shrub ‘Surgery’ for Spring 2/18/03

MANHATTAN, Kan. – "Surgery" often is safest for shrubs just before or as they leaf out in spring.

"That allows the wounds to heal quickly with less threat from disease," said Ned Tisserat, plant pathologist at Kansas State University.

"Insects shouldn’t be a threat, either. And you won’t have to treat the pruning cuts with paints or sealers. In fact, some of those products might actually retard healing," said Ward Upham, K-State Research and Extension horticulturist.

A growing movement in modern landscape design is to let shrubs grow naturally – for example, to let a forsythia produce arching branches, rather than try to make it a formal "ball," Upham said.

Shrub Pruning, in Short

1. Thinning. With shrubs that grow from multiple stems/trunks/canes at ground level (spirea, forsythia etc.), you can completely remove the oldest canes. With sprawling evergreen "groundcover" shrubs, you can simply remove or cut back the branches that are on bottom. Otherwise, however, thin shrubs by removing most inward-growing twigs – cutting back to a larger branch or to just above an OUTWARD-facing bud.

2. Heading back to reduce height or width, to foster shrub density, or otherwise establish shrub shape. Remove branch ends by cutting back to just above a bud. To prevent a "witches-broom" effect, do NOT cut branches to a uniform height. On upright evergreen shrubs, do NOT remove the leader at the top unless you can tie another healthy branch up to take its place.

3. Rejuvenation – only for multi-stemmed shrubs that are too big or that have too many old branches to justify saving the younger canes (in Kansas, typically spirea, forsythia, pyracantha, ninebark, Russian almond, little-leaf mock orange, shrub roses, flowering quince). Cut all stems/trunks/canes back to 3- to 5- inch stubs.

Source: K-State Research and Extension horticulture

"Some gardeners still seem to think pruning is a yearly necessity. But it doesn’t have to be unless a shrub has a problem," he said. (See related story.) "You should get rid of diseased, dead or damaged branches whenever you notice them. Sometimes you also can rejuvenate an old, leggy shrub through pruning in spring.

"The reason most Kansans end up pruning, however, is one they can avoid. They just need to buy plants that will fit the space when fully grown and won’t interfere with activities or structures. This includes buying plants that naturally conform to the desired shape. For example, some privets and evergreens lend themselves to hedge and background plantings with almost no shaping."

The specialists said timing for pruning is confusing only as it relates to this year’s flowers, not shrub health:

* Spring-bloomers that flower on wood produced last year, such as forsythia, lilac and mockorange, won’t have as many flowers if the pruning is done early. So, many gardeners prefer to wait until just after blooming.

* Summer and fall bloomers that flower on this year’s growth, such as Rose-of-Sharon, Bumald spirea and Japanese spirea, will flower best if pruned before they start the current season’s growth.

* Shrubs with no flowers or flowers with little ornamental value are best pruned in late winter or early spring.

In most cases, Upham said, the last category can also include Kansas’ common evergreen shrubs. For best shrub health – and often shrub appearance – however, gardeners should trim evergreens when diseases are not prevalent.

"Junipers and arborvitae, in particular, need pruning before May. Otherwise, you could be laying them open for disease," Tisserat said.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.