This is one of my favourite shrubs, despite its propensity for suckering and potential for high-maintenance. Common lilacs are ubiquitous, rock-solid hardy, insect and disease resistant, supremely drought-tolerant, and essentially bomb-proof. Actually, if someone let off some explosives on a lilac, I’m sure it would happily “sucker back” the next year and create a lovely shrub. It is available in a range of colours from light to dark purples, to blue, pinks, and white. Lilacs have many uses, from the traditional wind-break on farms, to specimen plantings in trendy, inner-city front yards, to privacy barriers in back-yard gardens. Common lilacs make excellent hedges, either formal or informal, and I consider a properly manicured lilac to be the best hedging material on the Prairies, eclipsing cotoneaster and caragana due to its disease-resistant nature.
Depends on the application and your tolerance for maintenance. Formal hedging should be carried out after the growth flush, preferably mid-summer onward. The hedge will likely need a touch-up trim in late summer to keep things looking neat. Prune anytime for specimen reinvigoration, although I always prefer to prune lilacs when the leaves are off so I can see what I’m doing.
Most commonly, we are called upon to clean-up or “reinvigorate” overgrown specimens. This means we remove the majority of the suckers and deadwood, selectively thin the stems from the base of the plant, and create an attractive, clean-looking shrub, with a pleasant “snow-cone” shape. This is tedious, time-consuming work but will transform an ugly, old lilac into a show-piece of the garden bed. It is worth the effort. If kept up annually, the pruning is minimal, a few suckers at the base and a bit of deadwood.
Ideally, trim formal hedges with sharp, long-handled hand shears, as opposed to the power hedgers. For budget and time constraints, we often use power hedgers followed by a quick hand-shear touch-up when working for clients. On my own hedge, I would spend the time and effort and use shears only. They make a nice, clean, scissor-like cut, and the edge of the leaves won’t “brown-off” after trimming.
If you want a privacy screen but don’t appreciate the bulky width of a mature lilac, try trimming only the sides of the hedge but leave the top alone. To me, this will give you the best of both worlds: a neat, crisp side-cut, with a beautiful, fragrant, flowering top. A mature lilac will max out around 15′ tall, so this method gives you a great privacy wall to block out a bad view or unfriendly neighbour.
(c) 2015 Shane LePage, Wild Rose Garden & Tree Service Inc., Red Deer, AB