The heavenly scent of lilacs has begun to drift around on the spring breezes, which carry the fragrance from my two French hybrids directly into my kitchen window.
What? This isn’t happening at your house? Your lilac is way out in the corner of the yard somewhere, and not positioned to take advantage of the prevailing westerlies? Too bad. And you aren’t getting ready to cut armloads of blossoms to perfume your rooms? Really too bad.
Older lilacs can be disappointingly shy of bloom, leaving gardeners despondent about shrubs that bloomed once — three years ago — and not again. Without their Rubenesque trusses of fragrant flowers, lilacs are just another big, green bush, right? I’m here to help.
Let’s think first of location. Lilacs need lots of sun to produce flowers, at least six hours of direct light daily. This is on the high end, similar to what is required for roses, say, or vegetables.
Perhaps, in your leafy suburban neighborhood, the trees have grown up around your lilac since it was planted, depriving it of sun. There’s precious little you can do, because a lilac wants what a lilac wants. You can: a) move the lilac; b) trim the trees; or c) plant another lilac in a more open location.
Maybe, if you’ve planted it recently, your lilac is just immature. Young plants need two or three seasons to establish a decent root system before they hit their flowering peak. Meanwhile, you can help it grow big and strong by keeping it watered, since these plants suffer in a drought. That’s not a sprinkle, but a good, deep soak every week or so during the first season if rain doesn’t fall.
As with all newly planted shrubs, you should keep groundcovers, grass and weeds away from the base of the plant, since they rob it of water and nutrients. A nice blanket of mulch helps to retain moisture, but don’t pile it up in a volcano-like mound around the base, or you’ll be inviting mice to nibble the bark away on a cold, winter’s day when the mousy larder is bare.
Although lilacs are easy to grow and hard to kill, they wouldn’t mind a little fertilizer, especially in the early years. Don’t overdo it, though, since too much nitrogen and too much fertilizer in general will get you big, healthy leaves but not much flower power.
Nutrients will go wasting if your soil is too acidic. Lilacs are lime-lovers, preferring soil with a pH reading of 6 to 7.5 on a scale where 7 is neutral. If you live in a pine and oak woods, or on thin, sandy Pine Barrens soils, chances are your soil is on the acid side. If you need to lime your lawn, you’ll need to lime your lilacs.
I inherited some truly ancient lilacs, since fallen prey to borers and rot and replaced outright. I did find that a serious pruning and a single dose of superphosophate (available at garden centers) kick-started them into blooming more prolifically. Follow the dosage recommendations on the package and water it in well. Phosphate is the element most associated with the production of fruit and flowers.
If you have been trimming back your lilacs in fall or winter, there’s a simple reason why you have no flowers. You’ve cut them off, silly. Flower buds are formed in early fall, primarily on the current season’s growth. The correct time to prune is immediately after the lilacs have bloomed in spring. (Obviously, cutting all the flowers you want will do no harm.)
Pare away crossing branches to open the center of the bush to light and air. Head back those tall limbs waving overhead by about a third to put flowers within reach. On established plants, get the saw out and cut to the base one or two of the oldest, thickest branches to allow younger ones to develop.
As for deadheading spent flowers, experts are divided on whether this will boost the blossom quotient next season. This can be quite a chore on a big, sprawling bush; I just cut flowers for the house with abandon and leave it at that. Yearly pruning to promote new, flowering wood is really more important than clipping every faded flower truss away.
If you’ve done everything right and your lilac still won’t bloom, here’s a final trick I learned from a specialty grower in Maine: Scare it. Make a scrape in the bark 2 or 3 inches long near the base of the trunk right after blooming season.
The theory is that by stressing the plant, you frighten it into producing seeds so that it — or its progeny — will survive the threat. And what precedes seeds? Flowers, of course. Just don’t overdo it, since girdling the trunk (removing a ring of bark completely around the circumference) will almost certainly kill it. And then you’ll have no flowers at all.