“Our lilac bushes have started sprouting from the roots, despite weed blocking fabric and rock mulch. What can we do to kill these unwanted sprouts without harming the main plant?” -Elizabeth
Lilacs are known for what is called “sucker growth,” which is when the plant sprouts from the root system. Some varieties are more prone to sucker growth than others. Unfortunately, they’re hard to control, because the more you damage the roots by digging or cutting the suckers, the more the plant produces – it’s a stress response.
Since your landscape fabric didn’t work, here are a few things to try:
- You may need to go with a thicker plastic barrier cloth. Weed control fabric works mainly by blocking sunlight and seed germination – it doesn’t stop shoots and roots from penetrating the fabric. A plastic barrier should prevent all growth, but it also blocks water and nutrients and holds in heat – you’ll need to keep an eye on any plants surrounded by such a barrier to make sure they aren’t cooking.
- Monterey Sucker Stopper is a commercial product containing the growth inhibitor NAA (napthaleneacetate), designed to stop growth of suckers from roots and pruning wounds. It is widely used in the orchard industry but is available for home gardens in a ready-to-use spray bottle.
- Remove suckers by tearing, not cutting. You want to remove the sucker all the way back to the root where it originates, and tearing them off will help remove dormant buds at the base.
- Dig them up with a sharp spade, removing the root as well. These can be transplanted if you wish.
- Prune the roots in a circle, using deep plunges of a sharp shovel, and then treat the suckers outside the circle with an herbicide such as Roundup®. Avoid spraying herbicide on any suckers still connected to the parent plant.
- You might also try surrounding your plant with a 6” – 12” deep underground barrier, such as buried metal or plastic landscape edging, to try to contain the roots. If your lilac is well established, its roots likely go deeper than this, but it can help.
- With root pruning or underground barriers, make the circle at least 2-3 feet wide, and ideally as wide as the shrub’s drip line.
Obviously, most of these tips will have to be repeated as the plant continues to sprout. I still have suckers coming up from a lilac I dug up and removed ten years ago – it’s not a battle easily won. Some gardeners deal with the problem by clearing more space around the shrub and just letting it spread, or by removing the shrub completely and having the roots ground out.