One of my favourite times in the yard is when the lilacs are in bloom. For some of you, that time has just passed and for others, it’s just getting started. Either way, this is the time to be paying attention to the lilacs in your own spaces.
The most popular lilac is the common lilac syringa vugaris, which is actually a cousin of the olive and is native to the Balkans. This flowering shrub has been a staple in the garden and although it is pretty, it also comes with several issues. Known to grow 20 to 25 feet, the common lilac is notorious for suckering. Also called offsets, these little shoots can pop up all around and even in the middle of the lilac bush.
The good news is you can actually grow new lilacs from these shoots. Just make sure that the leaves match those of the parent plant as some lilacs are grafted on rootstock of less desirable plants. This variety is also susceptible to several pests and disease, including powdery mildew, lilac blight and the lilac borer larva. Make sure to keep an eye on the leaves for signs of distress in your shrub.
Recently, I’ve started adding dwarf lilacs into the yard as a flowering hedge option. I love dwarf Korean lilacs for this purpose. The scents and the colours are fantastic, but for me, the fact that the bush only gets around four feet tall makes it ideal for shaping and pruning.
The key to pruning all lilacs is timing. You should only prune a lilac in the first three weeks after it finishes blooming. This is because lilacs take a full year to set their flowering buds. If you prune them in the fall, or even in the late summer, odds are you won’t have nearly as many flowers as the previous season.
There are a couple of tricks when it comes to the health of your shrubs. Lilacs need at least six hours of direct sunlight. Less results in a leafy bush with no blooms. Another big issue is our lawn fertilizers. Often we plant lilacs on the edge of the grass in our spaces. The nitrogen that we use for the lawn, especially the slow release variety, feeds the roots of the lilacs and cause them to increase their leaf development instead of blooms. Instead, choose a fertilizer with a higher middle number. This will promote more flowers from your shrub.
Add coffee grounds around the base of your shrub. Lilacs like an acidic soil. Keep it to a few cups of grounds per season, but the increased acidity will allow your lilac to absorb more nutrients from the soil around.
One more thing ... and this may anger a few gardeners out there, but pruning off the old blooms or the brown seedpods does nothing for an established plant. Don’t tell my mom though, she swears that she gets more blooms because she spends at least an hour every season trimming them off.
Carson Arthur is an international landscape designer and media personality with a focus on environmentally friendly design and low maintenance outdoor rooms.