A lilac tree variety such as Ivory Silk can reach a height of 30 feet and width of 25 feet. Cold hardy in USDA Plant Hardiness Zones 4 through 7a, Ivory Silk grows in full sun and produces a profusion of summer blooms, even on a young tree. Fall is the best time to dig up a lilac tree, as the tree is dormant at that time. The root system of a lilac tree is deep and wide, often creating a large rootball requiring two or more people to pull from the ground.
Measure the diameter of the tree trunk at breast level, between 4 and 5 feet off the ground. A study by the Journal of Arboriculture determined the diameter of a lilac tree at breast level is indication of the diameter of the rootball.
Multiply the trunk diameter by 14 to get the approximate diameter of the rootball.
Dig a trench around the perimeter of the tree wide enough to accommodate the rootball. Mark the cut line with flour, spray paint or a garden hose. While standing outside the circle and facing the tree, thrust the spade into the ground as deep as it will go. Push the spade toward the tree, creating a V-shaped trench.
Continue to dig down and toward the center of the lilac tree, freeing as much of the rootball as possible. Use a shovel to remove dirt to free the roots. A transplanted lilac tree is more likely to survive when as much of the root system as possible is included in the rootball.
Push the lilac tree to one side and work a rolled portion of canvas underneath the rootball. Use loppers to cut roots that extend beyond the expected rootball diameter. Push the tree in the opposite direction and unroll the canvas. Wrap the canvas around the rootball and trunk.
Secure the canvas around the trunk with twine, wire or sturdy cord and remove the rootball from the hole. Transport the lilac tree to a wheelbarrow or garden wagon to its new location.