Pruning Shrubs and Trees
Posted: March 20, 2017
In addition to improving a plant’s appearance, correct pruning promotes plant health and encourages flower and fruit development. Additionally, pruning hazardous trees protects you and your property. Here are some tips to follow when pruning specific plants, the best tools to use and some basic techniques.
Late winter, while plants are still dormant, is the ideal time for pruning many trees and shrubs. Pruning wounds are exposed for a short time before new growth and healing begins and you can see the structure of a deciduous plant before leaves obscure it. Prune apple trees (Malus pumila), flowering crabapples (Malus spp.) and cotoneasters (Cotoneaster spp.) now to reduce the chance of the bacterial disease, fireblight. Also prune maple (Acer spp.), birch (Betula spp.) and walnut (Juglans spp.) trees at this time as they have free flowing sap that ‘bleeds’ when they are no longer dormant. It is important to prune oak, especially trees in the red oak group, while they are dormant to prevent insects from entering pruning wounds and transmitting oak wilt.
Prune summer and fall flowering shrubs in early spring before buds break and the plants leaf out. These are shrubs that “bloom on new wood,” or the current season’s growth. They include sweetshrub (Calycanthus floridus), beautyberry (Callicarpa spp.), summersweet (Clethra spp.), bush honeysuckle (Diervilla spp.), smooth hydrangea (Hydrangea arborescens), PeeGee hydrangea (Hydrangea paniculata), summer-blooming spirea (Spiraea x bumalda and S. japonica) and repeat-blooming roses (Rosa spp. and hybrids.)
Immediately after flowering
Prune spring-blooming shrubs as soon as they finish flowering. These are the plants that “bloom on old wood,” meaning they set next year’s flower buds promptly after blooming. If you prune too early the plant will not bloom this year, and if you prune too late there will be no flowers next year. Spring-blooming shrubs include azaleas and rhododendrons (Rhododendron spp.), forsythia (Forsythia spp.), mock orange (Philadelphus spp.), ninebark (Physocarpus opulifolius), Virginia sweetspire (Itea virginica), spring-blooming spirea (Spiraea prunifolia and S. x vanhouttei), spring-flowering roses (Rosa spp.), lilacs (Syringa spp.), and viburnums (Viburnum spp.)
At planting time
Remove dead or broken branches when you plant the tree or shrub, then prune to shape during the following dormant season. Thin out branches for good spacing. Pruning is the best preventative maintenance you can give a young plant.
At any time
Prune a diseased plant at any time of the year. Remove the diseased parts as soon as you notice them. Sanitize your tools in a ten percent solution of household bleach (one part bleach to nine parts water) to prevent spread of infection.
When NOT to prune
It is futile to try to keep a large tree or shrub small with pruning, as it will always strive to grow to its predetermined size. Proper plant selection is more important. For safety, do not attempt to prune large established trees yourself, or take down hazardous trees, but contact a qualified tree care professional who has the necessary equipment. For advice on the safety and health of your trees, call an ISA (International Society of Arboriculture) certified arborist. Never prune near electrical and utility wires – contact your utility company. Do not top trees as this will result in vigorous, but weak upright growth called water sprouts. Topping opens the tree to internal decay making it more likely to break in the wind and heavy storms.
Equipment includes hand-held pruners, long-handled lopping shears, hedge shears, a pruning saw and a bow saw. Use the hand pruners on branches up to one-half inch diameter. A bypass (scissor action) hand pruner is preferred for close-cut precision. Use the lopping shears on branches one-half to one-inch in diameter and a bow saw for larger branches. The pruning saw is invaluable where the bow saw will not fit. You will need hedge shears for shearing shrubs into formal shapes; do not use hedge shears on trees. It is important to keep your tools sharp. When you use the bleach solution for sanitization, oil the blades afterward to prevent rusting.
- Remove dead, damaged, diseased or insect-infected branches first, then branches that are rubbing together.
- To shorten a small branch or twig, make the cut about ¼ inch above a bud, facing the outside of the plant so the new branch will grow in that direction.
- For large branches make three or four cuts to avoid tearing the bark. Starting about 18 inches from the trunk, make the first cut on the underside of the branch cutting half way through. Make the second cut an inch further out on top, cutting down until the branch breaks free. This eliminates the weight of the branch before making the third cut close to the trunk. The final cut will sever the remaining part of the branch from the main stem at the branch collar. Be careful to remove only the wood beyond the collar. The branch collar should be left intact but with no stub if the wound is to seal effectively without decay.
- Research shows that pruning paints are not necessary.
- When pruning hedges, shear the sides so the top is narrower than the base to allow the plant to get enough light.
- Overgrown shrubs such as forsythia and lilac may need renewal pruning: remove a third of the oldest stems or trunks right down to the ground to encourage the growth of new stems.
- You can rejuvenate badly overgrown flowering shrubs by cutting all stems back to the ground in early spring. The shrub will not flower that year but will return to its normal size and shape in one growing season.
Late winter in the Poconos is too early to do many gardening tasks, but it is a good time to check your shrubs and trees and begin to implement your pruning plan. Following these few basic tips can help you achieve a more beautiful landscape.
- Penn State Master Gardener of Monroe County