Look for an area on one of the lilac's main trunks where.

May 26, In the spring after it has bloomed, when you cut it back again, trim your lilac tree to one foot shorter than the height you want it to reach during springtime.

If you can't stand the look of your old lilac or you just want a quicker approach, you can take the drastic measure of cutting back the entire plant to about 6 to 8 inches above the ground in the early spring.

When you prune a lilac tree, you want to give it as much of a chance to be healthy and strong. Cutting it back like this is helpful to your lilac tree.5/5(1). Jul 08, Start by taking out the thickest stems first.

Although you'll be losing some flowers for the current year, pruning overgrown lilacs is easiest early in the spring before the branches leaf out. After three consecutive years of pruning your overgrown lilac in. Apr 02, If lilac bushes are already too large or becoming unsightly, however, pruning the entire bush or tree to about 6 or 8 inches ( cm.) off the ground may be necessary. Keep in mind that you may have to wait for flowers, as it takes about three years for them to develop once the entire shrub has been cut.

When to Trim Lilac Bushes.