Green Thumbs Up: Pruning tools and techniques

Suzanne Mahler

March is the ideal time to begin the process of selective pruning to produce balance, symmetry, direct growth, or rejuvenate old, sparse, or overgrown shrubs. Regular pruning will improve the overall appearance of nearly all woody plants, since few grow with perfect shapes, and even when selected appropriately for their allotted space, most benefit from an occasional trim to look their best.

The two basic approaches to pruning are heading back and thinning out. Heading back is the technique used for trimming a hedge — the entire shape is clipped, producing a more formal appearance with denser, sturdier growth.

Yews, hemlocks, boxwood and Japanese hollies are often shaped into geometric forms by this technique. The heading back of rhododendrons, azaleas, forsythia or other flowering shrubs into little round forms often spoils their individual beauty and character, although this approach is often necessitated by space limitations.

Hedge shears are the weapon of choice, with manual shears preferred for small jobs. Electric shears are faster and easier and permit greater accuracy of line for shaping hedges and larger specimens.

Thinning out produces a more natural, graceful appearance and tends to be the preferred technique for pruning woody ornamentals. When thinning out a tree or shrub, step back and observe the shape and structure of the plant before you begin the pruning process. Remove only those branches that are crossed or crowded without changing the basic form of the plant, unless you wish to modify its overall shape. Trim back individual branches, varying their length to produce a natural-looking yet compact plant. Up to one-third of a plant can be safely pruned away.

To ensure precise pruning, quality pruning tools are essential. Inexpensive pruners tend to produce ragged cuts because they are easily bent out of shape. Bypass pruners and loppers tend to be preferred by nurserymen, their scissors-like action making cleaner, closer cuts that facilitate healing. High quality pruners, like the Swiss-made Felco, are worth the additional cost for their durability and precision.

Avoid anvil-style pruners that have one sharp blade with an opposing flat blunt edge, as these may crush stems and produce uneven cuts. Hand-pruners are preferred for smaller branches, up to 1/2 inch across. Long-handled lopping shears are useful for cutting larger branches up to 2 inches thick.

Curved-blade pruning saws are usually designed to cut only on the pull-stroke and are ideal for larger branches and great for tight places. Bow saws cut on both the push and pull strokes but require more room to maneuver.

When pruning entire branches from the trunk of a tree, cuts should be made just beyond the ridge (above the branch) and the collar (a swollen area below the point of the branch’s attachment to the trunk). Sawing a branch too closely to the trunk may disrupt the healing process or produce new unwanted sprouts around the site of the wound, but do not leave stubs, which look unsightly and may lead to disease.

It is not necessary to apply paint to the wound — this may actually interfere with the plant’s natural healing ability.

To shorten a branch, always prune back to a side branch or bud. Cut the stem at an angle, and cut away from an outward facing bud to encourage growth away from the interior spaces of your shrub or tree (unless you are striving to fill a gap that may have been produced by storm damage).

Trees and shrubs that bloom in spring generally bloom on the previous year’s growth, known as old wood, and severe pruning just before new growth begins will significantly reduce their flowering. Forsythia, crabapples, plums and cherries, dogwoods, magnolias, azaleas and rhododendrons are just a few of these springtime delights. If you do not wish to sacrifice those lovely blossoms, prune spring bloomers immediately after they finish flowering.

Trees and shrubs that flower in late June or after tend to bloom on new wood. Spring pruning stimulates vigorous new growth and greater flower production for butterfly bush, sweet pepperbush (clethra), "Peegee" and "Annabelle" hydrangea. The popular blue and pink mophead hydrangeas are exceptions to the rules; although they produce their spectacular blossoms later in the season, their flower buds are formed on old wood at or near the end of the branches. Substantial fall or spring pruning of the stems will eliminate a majority of the flowers.

Suzanne Mahler is an avid gardener, photographer and lecturer who has been developing the 1.5-acre property surrounding her home in Hanover, Mass., for more than 30 years. She is a member of two local garden clubs, past President of the New England Daylily Society, an overseer for the Massachusetts Horticultural Society and is employed at two garden centers.