Answer: Wherever sunlight can penetrate, crabgrass will grow. You might want to consider weeding the area and then using a pre emergent herbicide along the foundation and under the first few inches of weed block. Check the pre emergence labels and buy one that prevents crabgrass. I'm afraid pulling and cutting back the crabgrass that grows near your lilac is about the only option. You won't want to apply weed killers too close to your lilac. Wish I had more suggestions!
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