Shearing hedges into cubes, globes, and squares is a form of architectural pruning that balances appearance with shrub health. This balancing act is most evident in the Pearl Fryar Topiary Garden in Bishopville, SC. Mr. Fryar, and now his protegee, Mike Gibson, Topiary Artist in Residence, skillfully maintain whimsical, fanciful living works of art from ordinary junipers, pines, and cypresses.
Regardless of your level of pruning prowess, which can be as basic as squaring off the tops and sides of your hedges, shearing impacts the growth and development of your plants. Every time you use your hedge trimmer or clippers, you prune away photosynthesizing or “food-producing” leaves and shoots. The shrub responds by producing bunches of leafy stems from behind each cut. When the new growth reaches a length that makes the hedge look scruffy, the cycle of removing and regrowing continues. Admittedly, dense, coiffed hedges possess an air of formality, even aristocracy. Underlying this visually appealing look, however, is the fact that frequent shearing affects the growth and longevity of the shrubs.
Peek inside the hedge. Observe the dense shell of leaves that surrounds the outer portions of the shrub and the bare stems below. This leafy shell sustains the entire shrub, including the roots. Many sheared evergreens exhibit no short-term ill-effects from shearing, but others, notably boxwoods, may gradually decline over time. Besides blocking sunlight, this leafy covering also reduces air movement in the interior, which can foster the growth and spread of fungal diseases. Fungal diseases common to boxwoods include Macrophoma leaf spot and Volutella leaf and twig blight; both can lead to injury and decline. For more information, see HGIC 2052, Boxwood Diseases & Insect Pests.
To reduce the effects of shearing stress, consider opening up the crown with selective reduction and removal cuts. A reduction cut shortens the length of a branch or stem back to a smaller lateral branch. A removal cut involves cutting back a branch to a larger main stem or trunk. Besides increasing sunlight penetration, it also improves air circulation. By adding 2 or 3 of these cuts to your shearing regimen will reduce the number of times you will have to interact with your shrubs to keep them neat-looking and tidy. Be aware that shrubs pruned in this manner will look more natural and less formal, but when you balance your aesthetic desires with the needs of your shrubs, it will prolong the life of your hedges. For more information, see HGIC 1053, Pruning Shrubs.