We have a large (12-15 ft) lilac in our backyard that has been there for longer than the 15 years that we have owned this house. The last few years I noticed that it was not getting as many leaves, and the blooms were smaller. This year, it is much worse – very sparse looking – and when I was weeding around it the other night, I didn’t do much more than touch a branch and it was so brittle it just broke off. I don’t see any evidence of disease on any of the leaves. I have heard some people say that lilacs have a lifespan, while others have said this isn’t true. Can I bring back my lilac and if so how (it provides important privacy in our small city yard), or is it time to replace it?
Actually, lilacs have a lifespan of more than 100 years so there may still be the opportunity to bring new life to your lilac. Pruning it back is a first step. Cut the overgrowth back in late winter or very early spring when the weather is still cold and the plant is dormant. When pruning an overgrown lilac, remove and discard the dead stems first. Go to the bottom of the shrub and remove the small suckers that are coming up from the ground or around the base of the bush. Then, stand back and look at the shape of the tree. Cut unwanted branches from the bottom of the shrub. Cut back tall branches to about 18 to 24 inches above the ground. Shape with pruning shears to the desired shape.
Once you have pruned your lilac back and it begins to show growth, be sure to fertilize and water thoroughly weekly during the summer and fall. Since your lilac is already well established, I would suggest you follow these instructions versus planting a new bush.