Shrub Pruning –Expand Your Diversity
“Arboriculture: The cultivation of trees and shrubs especially for ornamental purposes.” – Merriam-Webster
“Bring me a shrubbery … one that looks nice, and not too expensive!” – The Knights Who Say “Ni,” “Monty Python and the Holy Grail“
If that shrubbery is to remain looking nice, it’s going to need some pruning.
Seventy-five feet of driveway at my boyhood home was flanked by the house and a privet hedge bordering the neighbors. Being a hardy, fast-growing plant, the privet was in frequent need of taming. My dad was of an ilk unafraid to let his only son be furnished tools a pre-teen could now only dream of. Misguided in the value of labor, I repeatedly contracted my services for what in retrospect was criminally minimal. Thus, I unwittingly began my pruning career.
From hand pruners to hedge shears to electric hedge shears (complete with tattered and taped electrical cord) to an exceptionally hefty chain saw, the hedge endured my pruning research. I was able to get first-hand knowledge of what happens after one of my pruning “treatments.”
I went on to work with trees, but continued to have an interest in and offer services for small ornamental trees and shrubs. I have always found it extremely satisfying to transform an overgrown planting back into scale. Almost all of my tree clientele have shrubs. All the necessary tools were already in the arsenal, and it was great for days when tree work was prohibitive.
Most of the options described for shrub pruning correlate with tree-pruning terminology. Thinning, reducing, heading and rejuvenating are familiar and defined treatments. Of course, it all starts with “right plant, right place.” Try to accord the client’s goals with the reality of the situation. Ideally, the plant should be compatible with the cultural conditions of the site and placed so it can realize its potential. Failure to observe this basic premise often results in plants that are unhealthy, flower poorly (if at all), require extensive maintenance and have no semblance of their true form. If that’s the case, it may be best to remove the plant and replace it, or just let surrounding plants fill the spot.
My privet hedge was a case of the wrong plant in the right place. It offered excellent hardiness and screening, holding onto its foliage well into the fall. It was, however, exuberant on the south-facing site and needed to be kept at a minimal width given the driveway and the neighboring property. The goal, as it often is with shrubs, was retaining their size with minimal maintenance.
Thinning and reduction pruning, in my opinion, are the gold standards. They provide a more natural appearance and the opportunity to constantly rejuvenate the plant by reducing or removing larger, older stems while maintaining a consistent size. Cuts are made below the remaining stems, and are hardly noticeable to the casual observer. The downside is the labor. Cost limitations may make it untenable for many. Educating the client is the key. You cannot compete with powered hedge shears attached to a landscaper.
Shearing is an option for many plants. It creates a formal appearance, usually in some type of un-natural geometric shape. It is best done during the growing season. The later it is done in the growing season, the longer the tight form will last. For best results, foliage should be sheared to within an inch or so above the previous cuts. This, of course, results in a larger plant each year that will eventually need to be rejuvenated.
Rejuvenating a sheared plant or hedge involves cutting back well below the existing growth to form a plant approximately half the size. Be sure to create a tapered form to allow the lower parts exposure to light. Allow a season or two of growth and then resume shearing. Another option may be cutting the plant to the ground. Many species can be cut back in the early spring and will soon form a new plant.
Thinning a plant is a good option to revive older shrubs. In addition to appearance, the increased light and air flow reduce disease and insect issues. Remove dead, damaged and diseased parts and then approximately one-third of the oldest stems. Invasive species can often be found amidst the subject plants. Resist the temptation to cut these out and instead, remove them by the root. Cutting the stems will only promote new, hardier growth.
Slow-growing shrubs (most broad-leafed evergreens) tend to develop a more permanent structure and form most of their new growth at the terminals. They will expand slowly and, if it is the right plant for the location, will require little to no pruning. Shearing is sacrilege. Only occasional pruning to reduce an overgrown branch and enhance the shape, or light thinning to open up the plant to air and sunlight, should be performed.
Fast-growing plants are a different animal. They may need to be pruned on a regular basis to keep them from becoming a disheveled mess. Begin by removing dead, diseased and broken branches, along with any stems lying on the ground. Then remove up to one-third of the remaining stems, beginning with the oldest. Remove young, vigorous shoots without laterals growing up and through the canopy back to the base. At this point, you can shape the plant by reducing overextending branches back to a lateral, below the desired canopy. Try to make the cuts at different levels, and avoid any cuts on the perimeter.
Timing of pruning will depend on flowering and the importance thereof. Plants that flower in spring through early summer should be pruned just after flowering (i.e., andromeda, forsythia, lilac, mock orange, rhododendron, spirea, viburnum). Plants that flower in late summer (i.e., butterfly bush, beautyberry, various hydrangea, Rose of Sharon) are best pruned in late winter to early spring. Many plants are grown for their foliage, and their flowering is insignificant. These shrubs can be pruned in either time frame.
Additional considerations for timing include client expectations and maintenance costs. A plant pruned early in the growing season will likely look a bit unruly before long and require additional attention. Try to time pruning for later in the season, but refrain from late summer on.
For plants that become too large for the site, some species (i.e., certain cultivars of hydrangea, rhododendron and viburnum) can be pruned to a more tree-like form. Raising the crown, along with reduction and thinning cuts, can extend the life of a plant that can no longer be maintained laterally on the site.
Vines are also in the realm of arboriculture. As with shrubs, timing will be dependent on species and when the plants flower. In general, flower buds that develop on older wood should be pruned immediately after flowering. Those that develop on the current season’s growth, such as many clematis varieties, should be pruned in late winter/early spring.
Vines can grow upright in a variety of ways. Boston ivy attaches to surfaces by way of aerial roots, Virginia creeper with suction-like structures. They may be sheared close in early spring, before new growth appears.
Grape vines use tendrils, wisteria a coiling habit, to attach themselves to a support system, without which they would not climb. Pruning these types of vines requires forming a basic framework and pruning back to it to maintain size and health. The framework is formed by pinching back young vines to form several stems to train into the desired direction. The number of stems will vary by site, but three to five should be sufficient.
With vines, try to develop a system and compartmentalize your goals. You may occasionally come upon a situation that appears overwhelming. Begin by removing any dead or diseased stems back to their origins. Then remove any old parts of the framework back to a lateral or to its origin, as they become less productive. Young, vigorous stems growing beyond space limitations should be removed or, if needed, trained to the support system as a replacement for removed stems.
Vines such as wisteria will need to be pruned more than once per season for good results. Over the growing season, shoots growing from the main framework are headed back to two or three leaves. In the early spring, those cut shoots should be removed, leaving one or two buds. Growth from these basal spurs will produce the current year’s flowers.
Due to a tendency to overplant or use species too large for the site, foundation plantings are especially in need of conscientious pruning. Try to keep the cuts inconspicuous. Allow at least 2 feet of space from the building to allow for airflow and access. Remove a branch to the base rather than leaving it with sparse foliage.
Shrubs with more permanent frameworks (Taxus, Rhododendron, Chamaecyparis species) are subject to the same considerations as trees when making cuts. Heading cuts are made back to laterals no less than one-third the size of the parent branch. Refrain from leaving stubs and respect the branch collar. When making inter-nodal cuts, make them at an angle, just above a bud facing the preferred direction.
A good pair of hand pruners will be your best compadre, but tools of the trade have become more innovative and specialized. Compact, razor-sharp handsaws with thin blades and pointed tips allow for quality cuts in tight spots. Small, battery-powered chain saws can make a smooth cut in no time. Lightweight, battery-powered hedge shears are more ergonomic and, as a bonus, relieve the user from cord entanglement and risk of electrical shock.
Shrub pruning is not for everyone. A fusion of art and science, it requires the ability to envision the plant within the plant and make it so. It can be tedious and is far less thrilling than a crane pick, but the fruits of the labor may be quite gratifying.
Howard Gaffin, BCMA, RCA and Massachusetts Certified Arborist, is owner of Gaffin Tree & Landscaping, a 10-year TCIA member company located in Rowley, Massachusetts.