Garden: Rejuvenating Lilacs
The following is a regular column that addresses basic issues facing the ever-inquisitive back and front-yard toiler, proffered by the people who know best, the fertile master gardeners from the Berkshire Botanical Garden in Stockbridge. This week, they ponder the proper care of lilacs.
Sometimes in the garden, we don’t think about plant problems until they are staring us in the face. Often, however, the solution to these problems are things that take a fair bit of foresight — planting the right plant in the right place, soil quality, and in the case of this week’s subject, pruning.
I know some people who are so desperate to turn back the clock a few years that they would gladly give up a limb if that’s what it took. When it comes to rejuvenating lilacs, that is exactly what needs to happen. Lilacs are mostly in their prime right now (or just finishing up) and a lot of people notice that their older shrubs are leggy, with few blooms, and want to know why their plants aren’t weighted down with flowers like their neighbors’. The truth is, that for most species of lilac, the best blooms form on branches that are between three and five years old.
That means that you need to get rid of the old stuff. If you have older plants, you will want to plan this out over a three-year period, cutting back the oldest branches, all the way down to the ground, after the plant has flowered in the spring. This will encourage new growth throughout the growing season. Never cut more than 1/3 of the plant back at one time. Pruning all at once won’t leave the plant enough resources to encourage adequate new growth. The next year, cut out another 1/3 of the remaining old growth and repeat again the following year. You’ll also want to keep an eye on the new shoots, thinning as necessary to prevent overcrowding and to maintain the shape of the plant.
Once you’ve gotten your lilac back in shape, you’ll want to continue routine pruning to keep the plant looking young and fresh.