Tipping off your lilacs in this way will encourage them to sprout.
Jul 08, The general shrub pruning rule is to cut no more than a third of the stems each year. 2 That will help the plant remain constantly vital, with new stems developing as old stems bloom. Your goal is to have a lilac bush that has somewhere between eight to 12 stems of various ages, all of them between 1 to 2 inches in stumpdelimbing.clubted Reading Time: 6 mins.
Article is very specific.
A second way to prune old lilacs is to cut back the overgrown shrubs over a three-year period. Begin the procedure by removing one-third of the large, old stems at ground level in late winter.
The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of. Apr 02, The best time for pruning lilac bushes is right after their flowering has ceased. This allows new shoots plenty of time to develop the next season of blooms. Pruning lilacs too late can kill young developing buds. If you are pruning lilac trees or shrubs entirely to within inches of the ground, it is best to do so in early stumpdelimbing.clubted Reading Time: 2 mins.
Jul 14, Trim mature lilac bushes so that they remain within 6 to 8 feet. Aim to have 10 to 12 main stems, each of them 1 to 2 inches thick.
Never prune more than one-third of the bush. Create a balance of older stems and new flowering shoots.

Jan 09, Cut back 1/3 of the older lilac canes or branches. The following year cut out the next 1/3 of the oldest branches then the final year cut back the last of the oldest branches. Doing this in 1/3’s will let you have blooms and still cut back the old worn out branches fully renovating the lilac.