Lilacs will propagate by sending out shoots near the outside of the main plant. Perhaps the best time to replant lilacs is when the leaves are shed from the upper branches and the bush is in dormancy, according to New Mexico State University Master Gardeners. A well-prepared growing bed is necessary for the success of the lilac bush transplant. If possible, use a good source of compost to enhance root growth for the newly planted lilac bush.
Work the soil of the transplant area with the rototiller. Remove as many rocks and weed plants as possible.
Add a generous amount of rich compost material to the new growing bed. The more compost material you add, the better the chances for good root growth on the lilac transplant.
Dig the lilac bush from the ground using the shovel. Keep as large of a natural root ball as possible under the lilac bush. More intact roots lead to a more successful transplant.
Dig a hole in the transplant bed as wide and deep as the lilac's root ball in the center of the new grow bed and insert the lilac. Keep the existing soil level from the lilac transplant at the same level in the new grow bed. Backfill all soil around the root ball of the transplant. Tamp the soil around the roots with your hands.
Water the new transplant into the soil using the garden hose. Maintain a moisture depth of at least 3 inches around the lilac bush.
Add a layer of mulch around the lilac bush to discourage weed growth and aid in retaining moisture.