Lilac roots are both shallow and deep. If it is a mature Lilac you will not hurt it if you hoe 2 or 3 inches deep. You may find you will have a few Lilac shoots starting from where you cut through the roots. These shoots can be easily transplanted by cutting a root ball 8 to 12 inches deep and about a foot in diameter with a round nose shovel. I prefer to move these shoots in the fall as soon as the leaves drop and depending on height, may prune them back at the same time. Because I lived in zone 8, some limited root growth can occurr all winter and a little fertilizer in the spring sends them on their merry way. Others will dig and transplant these just as the buds begin to swell in the spring. Fetcher

OK thanks for your help