Dig, split and transplant lilac bushes in early spring prior to the leaves emerging from swollen buds. Perform this task after all threat of frost is completed in your climate. Damage to the roots can occur if exposed to any freezing temperatures. When splitting a lilac bush, only the new shoots or stems should be separated from the root ball. These new plants are then transplanted to other areas. The entire lilac bush will not be dug up. Only remove the new growth that lays to the outside of the established mother plant.
Use the pruning shears and remove any old and dead branches from the center of the lilac bush. This is not a required step, but removal of old or broken limbs will add vigor to the bush and the root system.
Identify the new shoot growth on the lilac bush. The new growth will reside to the outside edges of the branches on the plant. Typically new growth that can be separated will still be connected to the mother plant, but an individual root system is forming below the ground level. These new growth stems will range in height from 6 inches to 18 inches in length.
Dig new transplant holes prior to removing or splitting portions from the mother lilac bush. This will aid in keeping the air exposure to the young plant's roots to a minimum. The young roots may be susceptible to drying out, causing failure in the transplant. The transplant hole should be at least 12 inches in diameter and 18 inches deep. Loosen all soil in the hole. This will give the new roots a chance to spread after the transplant process.
Select the first of the new shoot growth from the mother lilac. Place the edge of the spade shovel to the inside of the lilac bush. In other words, the tip of the shovel must be set between the mother plant and the shoot you are going to remove.
Press down hard on the top of the shovel with your foot. Severe the small root structure from the mother plant.
Place the spade shovel to the outside of the new shot, just opposite of where you made the interior cut. Push the shovel into the soil. Pull back on the shovel's handle. Remove the new shoot from the soil.
Place the new transplant into the new transplant hole. Keep the soil line level with the existing ground. Backfill soil around the new transplant. Press the soil firmly into place with your hands.
Water the new transplant with the garden hose. Soak the transplant to remove any air from the root system. Add water to the lilac transplant at a rate of 2 inches per week until natural rainfall is equivalent for the first month.