The Kindest Cuts: Where and How to Prune

by Karan Davis Cutler

Even if you're not interested in becoming a pruning virtuoso, you don't want to be a botanical butcher. Any pruning stresses trees, shrubs, and vines—it's surgery, after all. A faultily pruned plant won't recover for years. Perhaps never. At the least, you need to know how to achieve your pruning objectives while doing as little harm as possible.

The term "pruning" has come to mean everything from cutting, pinching, delimbing, heading, and shaping to trimming, disbudding, topping, shearing, thinning, and more. Whatever the method—or the term—the pruner's aim is to keep people and property safe, and to keep plants healthy, productive, attractive, and in bounds. Over time you'll develop your own pruning techniques, but it never hurts to take advantage of others' knowledge and experience. No need to reinvent the pruning wheel.

However small or large the job—and whatever your goal—for the health of the plant:

Unless it's a topiary or hedge, respect the natural form of the plant when you prune. Don't overstress plants by cutting away too much at one time. Always cut back to healthy, living wood.
Make clean cuts. No ragged edges, no torn or bruised bark.
No hat pegs, as the British say. That means don't leave stubs and snags when you cut and saw.
Don't expect pruning to solve problems created by an inadequate site or poor maintenance.

And for your own health, use the proper tools, wear safety gear, know where limbs will fall, count your fingers, and keep your ladder upright.

The goal of pruning is to keep plants healthy, productive, attractive, and in bounds. Rhododendrons require little pruning beyond deadheading and removing very old wood.
Photograph: Walter Chandoha

Heading Cuts and Thinning Cuts

If you're a novice gardener, the place to start is with understanding the differences between and the effects of heading and thinning. All pruning begins with these two basic approaches.

Heading or heading back, is cutting off a portion of a stem or branch. Since heading eliminates the terminal bud, it forces new growth close beneath the cut. (See "The Why and When of Pruning" for more on the effects of removing terminal buds.) The more stem you remove, the more vigorous the new growth on the portion that's left. If you want to invigorate a plant, to encourage branching and bushiness, heading back shoots and limbs is the way to do it. Heading back, which is also known as tipping, is most effective with young stems.

When heading, make your cuts above a node—the point on the stem where buds, leaves, or stems are attached. Now the bud or buds just below the cut become the stem's new growing point, or terminal. Heading causes especially dense regrowth in maples (Acer), lilacs (Syringa), Clematis, and other plants with opposite buds, species with leaves that appear in pairs at each node, one on each side of the stem. That's because both buds form new growth. As a result, most woody plants with opposite buds tend to have a rounded shape, or at least a rounded crown.

On birches (Betula), roses (Rosa), passionflowers (Passiflora), and other plants with alternate foliage—one bud per node—heading back produces less branching but guides the direction of new growth. Cut to an outside bud—one pointing away from the center of the plant—and the new shoot heads in an outward direction; cut to an inside bud, and the new shoot grows in an inward direction. You'll want new stems heading out, which encourages an open habit and permits more sun and air to reach the inside of the plant. Unless there is a real need to "fill in" a plant's center, always cut to an outward bud.

Heading also affects flowering and fruiting because it alters the balance between above- and below-ground growth. The more stems and leaves you remove, the harder the plant tries to replace them—at the expense of flowers and fruits. Heading a young plant, especially, delays the development of flowers and fruits. Prune a mature plant lightly and blooms will be plentiful, but each will be smaller; prune severely and flowers and fruits will be larger but fewer in number.

Illustration: Stephen K-M. Tim

Heading was once standard practice for new trees, shrubs, or vines. Now that most nurseries and garden centers sell container-grown plants—which don't suffer root loss when transplanted—heading is not needed and is not recommended.

Heading the entire crown of a woody plant to reduce its height is known as topping, stubbing, or lopping. The approach, also called hat racking since the result resembles a hat rack, is used all too often by power, telephone, and cable companies to keep trees from growing into their lines. Garden writer Barbara Ellis describes a victim of topping as "a disfigured tree with a canopy of stumps." Trees that have been topped are unlikely ever to regain their natural form and are open to disease and sun scald. Their new growth will be thick but weak. Instead of topping a tree, replace it.

Topping overgrown shrubs and vines also stresses the plants, but sometimes it may be necessary—and can have more satisfactory results. Most vines respond fairly quickly, but plan on waiting several years for established deciduous shrubs to recover. Some—including many evergreen species—won't recover and should never be topped. Always think of topping as pruning of last resort.

Another form of heading is shearing, cutting back all the stems of a plant to follow a predetermined shape. Customarily reserved for hedges and topiaries, shearing works well with some species, such as boxwood (Buxus) and yew (Taxus), but would be disastrous—and possibly lethal—with a Rhododendron.

The easiest, safest, and most effective form of heading is pinching, using your thumb and index finger to nip out the tender growing tip of a shoot. No tools are required, wounds are small and close up quickly, and the plant doesn't look as if it has been scalped. Pinching slows growth—it's an effective tool for keeping plants small—and is virtually imperceptible.

Using proper technique will help avoid most pruning accidents, such as tearing off bark. Photograph: Chris Roddick

Thinning is removing an entire shoot, stem, or branch back to its point of origin, the main stem, a lateral stem, or even to the ground. Thinning opens woody plants, promoting good health by reducing foliage and allowing more air and light to reach their interiors. It is less invigorating than heading, produces less regrowth, and better allows plants to retain their natural forms. Thinning cuts are also used on woody plants to establish strong frameworks and to direct and shape growth.

Crown thinning, which is most commonly used when pruning deciduous trees, is the selective removal of center growth in the crown, or canopy, while maintaining the plant's natural form. Reducing the density of the crown and correcting asymmetrical growth are the usual reasons for crown thinning. Crown raising—also called lifting or skirting—refers to removing branches at the bottom of a plant, cutting back to the main stems or trunk.

Raising the crown may be a way to keep a plant that has overgrown its site—a pair of 40-foot Norway spruces (Picea abies) planted by the front door, for example—or the solution to the nothing-will-grow problem under the stately American beech (Fagus grandifolia) in the front yard. Raising the crown can open the view, reduce shade, and make plants more attractive. It isn't always an ideal solution—some plants, conifers in particular, look awkward without their bottom limbs, but lifting may be a better alternative than having to cut down a mature tree, shrub, or vine.

Renewal pruning of plants also involves thinning cuts, lots of them. Trees with a single trunk—and plants that have been grafted—are thinned of everything except the limbs you want to retain as the basic framework. Multistemmed plants can be renewed by cutting the stems to the ground, either all at once or over several seasons.

Know as much as you can about a plant's habit—how it grows, how it responds to pruning—before you attempt renewal pruning. Renewal pruning is a grievous shock to all woody plants, and they don't all respond the same way. Some species, such as mountain laurel (Kalmia latifolia) and many conifers, are famously intolerant of such manhandling. Even plants that ought to respond well to renewal pruning sometimes don't. I've cut a European cranberry bush (Viburnum opulus) to the ground a half-dozen times and it still comes back, but renewal pruning was lethal to my doublefile viburnum (Viburnum plicatum f. tomentosum). Renewing sometimes means replacing.

Upper Left: A tree is forming woundwood aroudn the perimeter of a proper pruning cut. Upper Right: Eventually, the tree will close off the wound completely. Lower: If the bark on the trunk or the branch collar are injured when a branch is removed, the tree cannot form woundwood properly and is open to infection by pathogens.

Top Left: A tree is forming woundwood around the perimeter of a proper pruning cut. Top Right: Eventually, the tree will close off the wound completely. Bottom: If the bark on the trunk or the branch collar are injured when a branch is removed, the tree cannot form woundwood properly and is open to infection by pathogens. Photographs: Neil Soderstrom

Making the Cut

Before you rip into pruning your trees, shrubs, and vines, have the appropriate tools and be sure that they are sharp and in good repair. Hand pruners are made for small cuts, loppers and pruning saws for bigger jobs, and pole pruners and saws for limbs you can't reach from the ground. Most pruning cuts are pretty straightforward, but there are a few tricks you should know.

Small Cuts For jobs that can be done easily with pruning shears—cutting shoots, stems, and branches less than one inch in diameter—you have two choices. If you're heading, cut back to a bud that is pointing in the direction you want the new growth to go. Ninety-nine percent of the time, that will be an outward-facing bud. Cut about a quarter inch above the bud, and slant the cut away from the bud; with opposite buds, cut straight across the stem. (Cut closer than a quarter inch and you're likely to damage the bud; cut farther away and you'll leave a stub to decay.) Rather than head all stems to the same length, vary their lengths. That way, your plant won't look as if it's had a crew cut.

If you're removing an entire stem or limb—thinning, rather than heading—cut to an outward-facing branch that has a crotch angle of no less than 45 degrees to the branch you're taking off. Be careful, too, that you don't slice into the connective tissue of the branch that will remain—cut about half an inch above the branch you're cutting to.

Large Cuts Big thinning cuts—those made with a saw—are harder on plants than snips made by shears or even loppers. Big wounds close up more slowly, leaving plants open to infection. Always try to cut back to a branch with a diameter that is at least half as great as that of the limb you're removing. When taking off large limbs, either dead or living, be sure to cut to—but not into—the branch collar, the swollen area surrounding the base of a limb. Arborists once recommended flush cuts, sawing as close to a limb or trunk as possible. No more. Botanists have discovered that the branch collar helps the plant to form a chemical barrier against pathogens that may attempt to enter through the open wound. It gives the plant protection while it closes up the cut surface with woundwood.

A poorly executed cut caused a large section of bark to tear off.
Photograph: Neil Soderstrom

Just above the branch, on the wood you're cutting to, you should be able to see the branch bark ridge, a dark bark line that runs approximately parallel to the branch you're removing. You don't want to cut into the branch bark ridge either. Depending on the tree species, the branch collar and the branch bark ridge may be more or less obvious. If you have trouble finding them, look for older pruning cuts on the same tree or another tree of the same species. Cuts that have closed up properly will give you an indication of what the branch attachment looks like and will help you find the right area and the right angle for your pruning cut.

To thin a large lateral branch—one more than two inches in diameter—cut as close to the remaining limb or trunk as you can without cutting into the branch bark ridge or the branch collar. The cut should angle away from the wood you're cutting to. It often helps to have another pair of hands to support the branch you're removing so that when it falls, it doesn't damage or strip the bark of the limb or trunk to which it's attached. (If the branch isn't too heavy, use your free hand to provide support and slow the fall.)

The Three-Cut Technique

When removing large limbs it will be necessary to use a three-cut technique to avoid damage. If you'd rather be safe than sorry, use this technique every time you work with a saw rather than hand pruners.

Illustration: Paul Harwood

Step 1 Notch under the limb upward, 6 to 12 inches from the trunk or branch, stopping before the saw binds.
Step 2 Cut through the limb from the top, 1 to 3 inches beyond the underneath notch until the limb falls.
Step 3 Remove the remaining stub, cutting just outside the branch collar and bark ridge.

If you're heading a secondary branch, cut to a limb that is at least one third the diameter of the one you're taking off. Follow a three-cut technique for large limbs so that you don't strip bark from the remaining branch. First, make a V-shaped notch on the side of the branch away from and about eight inches above the node you're cutting to. Second, from the opposite side and just above the notch, make a second cut through the limb. Third, remove the stub. Make your cut as close as possible to the branch collar, but don't cut into the collar or the branch bark ridge. The size and angle of the collar vary greatly from one tree species to the next and vary somewhat between trees of the same species, which means the ideal angle for the cut will be different each time. Don't rush this step: The quality of your final cut determines whether or not the wound will close up properly.

Should Tree Wounds Be Dressed?

As a general rule, don't dress. Tree wound dressings, a.k.a. pruning paints, once were standard treatment for cuts larger than an inch or two. The theory was that they prevented disease and insect damage to (and through) the wound. More recently, researchers have established that bituminous paints and other wound dressings not only don't prevent damage, they may do damage by slowing the formation of woundwood. (In a very few regions, wound dressings are recommended for particular species as protection against specific diseases; for example, against the spread of oak wilt in some parts of Texas. If you're pruning an old and valuable tree, check with local specialists.)