When, Why and How to Prune Trees and Shrubs

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A Tree Steward volunteer uses a pruning saw to trim a young tree at Claudius Crozet Park. Photo: Bill Sublette.

By Chase Giebner and Bill Sublette
Piedmont Master Gardeners   

Careful pruning can improve the health, strength and structure of trees and shrubs. But before you head out with your saw and clippers, give some thought to whether it’s the right time to prune, why you’re pruning, and how to do it safely and efficiently. 

Safety First 

Job one is to protect yourself: wear long sleeves, gloves and safety glasses. All it takes is a stray twig or wood chip to cause a serious eye injury. Add ear protection if using power tools such as a hedge trimmer or leaf blower. 

As you work, be mindful of your body position. The pros will tell you it’s easy to injure your non-dominant hand when sawing and snipping. If making a cut requires leaning precariously, stop and reposition yourself to get a better angle. If you need a ladder to reach your tree care work, think twice. It may be time to find a certified arborist. Search online for “ISA certified arborists near me.” 

Tools You Will Need  

Virginia Cooperative Extension has produced a series of helpful pruning guides that are available online. Search for VCE publication 430-455 (“Pruning Basics and Tools”) to find a concise overview of tools—from pruning saws and hand clippers to loppers and pole pruners—and how they should be used. Use “bypass” clippers and loppers rather than the “anvil” type, which tend to crush stems as they cut.  

When to Prune 

As a general rule, midwinter is an ideal time to prune deciduous (non-evergreen) woody plants. 

In this dormant season, cuts will result in less sap loss and are less likely to introduce pests and disease. Pruning trees toward springtime will optimize the growth of healthy material that covers wounds, like a scar. Oaks, which face a variety of pest and disease threats these days, should be pruned in November or December and no later than February. Never prune them in the growing season. Avoid pruning all trees and shrubs in late summer or early fall; this can stimulate tender new growth that will be vulnerable to cold damage in the coming winter months.    

Most flowering trees and shrubs should be trimmed after their blooms fade so as not to remove the buds that formed on old wood in the previous growing season. The recommended span for pruning redbuds and serviceberries, for example, is May through July. Crape myrtles, which set their flower buds on new wood, are an exception. They should be pruned right now through March. 

Virginia Cooperative Extension offers detailed calendars for tree and shrub pruning. Search for VCE publication 430-460 for deciduous trees and for VCE publication 430-462 for both deciduous and evergreen shrubs.  

Prune Trees While Young 

Pruning is an injury to the plant and should be done only when necessary. For trees, the aim is to remove any material that is dead, damaged, diseased or in the wrong place. 

The top priority is to remove dead branches, recognizable this time of year by the lack of viable buds. Do this if nothing else. It will improve a tree’s vigor and appearance while reducing the danger of limbs coming down in high winds. The next priority is to remove limbs damaged by storms, disease, pests or deer and other wildlife. When pruning diseased wood, clean tools between cuts with a disinfectant such as rubbing alcohol. 

To improve a tree’s structure, prune it while it is still young and its upper branches are still reachable. This will save labor, expense and potential safety problems in the years ahead. Moreover, younger trees are better able to recover from pruning than older specimens. That said, you should prune as little as possible the day you plant a tree. Wait two to three years. 

Keeping in mind the tree’s natural shape, make room for new growth and air flow in the canopy.  Remove crossing or rubbing branches, branches that would keep light from reaching those below, and branches with narrow or weak connections. Preserve branches that form wide angles of attachment to the trunk; they will become the tree’s permanent scaffolding. Trim away suckers and thin out “watersprouts” that pop up on the trunk or branches. 

While a tree is young, choose a single, main stem that will become its permanent leader and remove or cut back any co-dominant stems. If allowed to mature, a co-dominant stem will form a weak connection with the main trunk, increasing the risk of failure in the future. Also, act early to remove tree branches that in time will brush up against a wall, block desirable views, reduce visibility for drivers and pedestrians, or impede traffic. Remember that a branch will not move up as the tree grows but will remain at the height where it formed.  

Making the Cut 

Before removing a branch, take a moment to find the “collar” where the branch forms. Flush cuts used to be the norm, but now we know that preserving the branch collar will promote healthy sealing of the wound. Leaving a stub will also hinder wound sealing and should be avoided. 

Preserving the branch collar promotes sealing of the wound. Photo: Bill Sublette.

When removing branches more than an inch in diameter, use the three-cut method to prevent bark tearing. About 12 inches out from the branch’s source, make a first cut from underneath about halfway through the branch’s diameter. Just beyond this cut, remove the rest of the branch to reduce its weight. Make the final cut at the branch collar, as noted above. For more details on proper cutting (and helpful illustrations), search online for VCE publication 430-456. 

Pruning Shrubs 

Shrubs should be pruned to remove damaged material, to maintain desired shape and size and to bring light and air into the plant. In Virginia Cooperative Extension’s guide to pruning shrubs (search for VCE publication 430-459), authors Susan French and Bonnie Lee Appleton describe two basic types of cuts for shrub pruning. Thinning cuts remove branches to their source and are used to reduce shrub density without stimulating regrowth. Heading cuts are made just above a bud at a slight angle and should be used selectively to reduce the height of the shrub. Be aware that heading cuts will stimulate new growth below the cut in the direction of the remaining bud.  

The growth habit of a shrub dictates how it should be pruned. For mounding shrubs, such as evergreen azaleas or spirea, the authors recommend pruning only the longest branches and then making thinning cuts to branches inside the shrub where they won’t be visible. This method reduces the shrub’s size while preserving its natural shape.  

For shrubs that send up fountains of cane-like branches, such as forsythia, cut the tallest canes to near ground level, take out canes crowding the center, and remove canes growing in unwanted directions. For shrubs with a tree-like habit, such as witch hazel and rhododendron, remove any rubbing branches, suckers coming up from the roots, and branches that bend down to the ground. Carefully use thinning cuts to open up the center and bring in more light. As a final step, use heading cuts to reduce the shrub to its desired height while maintaining its natural form. 

To rejuvenate old, overgrown shrubs, French and Appleton recommend two methods. Drastic pruning reduces the entire plant to just 6 to 10 inches above ground. It should be done in early spring just before bud break. At midsummer, remove half of any new canes that come up, and trim some of the others with head cuts that promote outward rather than inward growth. Shrubs that can tolerate this treatment include abelia, hydrangea, lilac, spirea and St. John’s wort (hypericum), among others. 

A more gradual approach involves removing one-third of the oldest, unproductive branches the first year, half in the second year, and the remainder in the third year. This technique requires patience, but it is easier on the plant—and the eye.  

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