Ask Mr. Smarty Plants

The common lilac, Syringa vulgaris, is a native of Europe and Asia; therefore, we have no information on it in our Native Plant Database. We can understand your wishing to keep your lilac, even though at the Lady Bird Johnson Wildflower Center we encourage the use of plants native to North America and to the area in which the plant is being grown.

We looked and looked and looked without finding anything about damage to a foundation from lilac roots. Since they won't grow in hot country like Texas, we have no personal experience with them. We did find information that growing them over a septic field was not a good idea. Finally, in an article by Ron Smith, Horticulturist for North Dakota State University Extension Service, Questions on Lilacs, we found this question and answer:

Q: I have lilac bushes that apparently are planted too close to the foundation of my house. I’ve been told to move the bushes so they don’t cause a problem when they get bigger (with the drain tile and the foundation). How do I remove the bushes? Can I replant them in another location? When is the right time to do that?

A: I doubt the lilacs will be a problem to your drain tiles or foundation. If you still want to move them, now is not a good time. Early next spring or late this fall, after the foliage drops, would be better.