Is there a way to rehabilitate this lilac bush? It's gotten really leggy, and has all those suckers(?) growing underneath. It didn't flower well at all this year, and it had flowered beautifully last year. Could the mildness of this past winter have something to do with that? I've heard that you can cut back a lilac to 2 or 3 feet, and that it won't flower the following year, but will fill in and flower the second year after it's been cut back. Is this true? Thank you.
Carroll County Maryland
Thank you for your question.
You can and should prune old wood from lilacs on a regular basis. The rule of thumb is to cut back no more than 1/3 of the plant at any one time, removing the oldest wood first.
What you see is common on lilacs and not just because of the past winter. Wood that is too old ceases to flower well. A folding pruning saw is the ideal tool, but any gardening saw small enough to work among the stems should suffice. This is a multi-year project (to give the plants time to recuperate and re-grow) that gradually removes all old wood to encourage vigorous new replacement growth. It could be done all at once, but that may unduly stress the plant and will eliminate all flowering for the following two or more years. The younger shoots that regrow will flower better (once mature enough) and are not attractive to pests such as lilac borer. Below are links to a video demonstrating the procedure and a description of how to prune:
Once the lilacs have reached a more youthful, vigorous state, such drastic pruning will not be regularly needed except to periodically remove aging stems here and there. Maintaining full sun exposure (6+ hours a day in summer) will also help them flower to their fullest potential.