Answer: The roots of your lilac have lots of stored energy so even if you completely cut the top down, the stored energy is capable of producing new shoots. If you keep the shoots cut down before they grow leaves (which transports more energy to the roots of the plant), the roots will eventually run out of energy and will not be capable of sending out new shoots. This can be labor intensive over a period of several years. Another way to attack the problem is to make a fresh cut in the stump of the plant and paint the cut with an herbicide such as undiluted Round-Up or Fertilome Stump Killer. These herbicides can take some time to work but they are effective when applied according to label directions.
Q&A Library Searching Tips