Transplanting large lilac bushes may be a job for a contractor since the bush plus the root ball could weigh a few hundred pounds. Smaller lilacs, or the root suckers of large bushes, transplant well at most times of the year but planning and timing increase chances of success. Dividing a bush properly and transplanting only part of the plant could be much more practical than moving an entire bush. Large lilacs need years to recover after relocation.
Move lilac bushes in the early springtime before the leaf buds open, when winter stresses are past and the plant prepares for vigorous growth.
Judge the size of the root ball required for mature lilac by the diameter of the bush's canopy. Plan for a ball of soil and roots two-thirds the diameter of the spread of the bush.
Dig a trench at least 1 foot deep around the perimeter of the root ball. Use the mattock or pulaski to cut any large roots extending beyond the ball zone.
Press the transplanting shovel under the root ball to cut the bush loose. Work the entire perimeter of the root ball with the transplanting shovel. Use the blade of the garden spade for lifting leverage and to access the deeper zones beneath the bush.
Lift one edge of the root ball with the garden spade and work the edge of the tarp underneath the bush's roots as far as possible. Tip the bush away from the tarp to work the cloth past the center of the root system.
Lift the lilac bush and root ball by the stems of the plant and slide the root ball onto the tarp. Using the tarp as a lifting device, place the bush in the cart. Keep the tarp wrapped around the root ball to prevent feeder roots from drying out.
Push the cart and the bush to the new location, transplanting to a new hole slightly larger than the root ball of the lilac bush. Add good topsoil to the site to fill in the empty spaces and then water the plant thoroughly.