Pruning Shrubs

By John Wilson

Extension Educator

John Wilson

After a long, cold winter, we’re finally getting some warmer weather. For those that have been stuck inside too long, this will give you a chance to tear yourself away from the Olympic coverage and do some things outside. This is a great time to do some pruning on shrubs in your landscape.

Correct pruning is important for shrubs, but it’s easy to overlook this project. Without pruning, or with incorrect pruning (such as shearing), shrubs tend to become a tangled mess of stems. They end up too dense with dead centers and spindly branches with few leaves on the lower half of the plant.

Most deciduous shrubs, those that lose their leaves in the fall, are correctly pruned by thinning out rather than shearing or cutting back their height. Shearing results in branch ends that produce dense growth that shades out the rest of the plant, causing the lower branches to become bare and weak. Thinning helps shrubs maintain a natural growth habit, vigor, and attractiveness.

Shrubs are often sheared to control size. However, the desired height and width of a shrub can be maintained for many years with thinning cuts. By thinning, it is also easier to see branches that are suckering up from below or resting on the ground and rooting down. These can then be removed to control a shrub’s width or spread.

Using a hand pruning shears, not a hedge shears or trimmer, thin shrubs by removing the oldest and tallest branches where they attach to another branch or back to an outward facing bud on the stem. The reason for pruning to an outward facing bud is to encourage new growth to grow outwards rather than towards the center of the shrub. This allows more sunlight into the shrub.

If a shrub has not been pruned in some time, remove all dead branches before thinning live stems. If this is an overwhelming job, a shrub can be renovated by removing a third of the largest and tallest stems clear to the ground each year for three years.

Neglected shrubs, those with a lot of dead wood or that are too dense to effectively thin, can be cut at ground level for complete renovation. Don’t leave a stub 6-12 inches sticking up, take it off at ground level. Those stubs of old wood may attract borers and weaken the shrub. I call this “chain saw pruning” but I’ve used it and it is quite effective.

You may sacrifice blooming for a couple years, but it can be the easiest method to rejuvenate old, neglected shrubs. These will regrow much faster than if you set out a new shrub because it has a mature, established root system to support the regrowth. Be sure to thin out the shrub each season thereafter to avoid an overgrown mess again.

The ideal time to prune most deciduous shrubs is from now until the buds start to swell in the spring. Wait to prune spring flowering shrubs until after they bloom unless a renovation type pruning, where over 50 per cent of the plant will be removed, is planned. In that situation, it is best to prune when the shrub is dormant.

If spring blooming shrubs are only in need of a small amount of thinning, consider pruning them before they bloom, then bring the branches indoors to force them to bloom. Spring-flowering shrubs and trees set their flower buds the previous summer. Once flower buds are exposed to cold for a few months, usually by mid-January, a branch can be cut and forced to bloom indoors.

Some of the easiest branches to force are forsythia, pussy willow, honeysuckle, crabapple, and redbud. Look for branches with many flower buds. These will be larger and fatter than leaf buds. Cut a few branches, about six to eighteen inches long. Always cut just above an outward facing side bud or where the branch attaches to another branch. Remove branches from crowded spots to help thin the shrub.

Place the branches in a vase of cool water. The flower buds will open indoors in one to five weeks, depending on the plant type. The closer to the natural blooming time the branches are cut, the shorter the wait until forced branches will start to bloom.

For more information on pruning shrubs, contact your local UNL Extension office.