The best time to rejuvenate large, overgrown shrubs is late winter or early spring.
Apr 28, To prune lilacs, get to work in the spring: cut fresh flowers for bouquets, nip off the longest stems, and thin out any weak stems at the base.

Avoid pruning late in the summer or fall since doing so can limit future growth. Part 1 Doing an Annual Pruning75%(4). Feb 05, Subscribe Now:bushdelimbing.club?add_user=ehowatHomeChannelWatch More:bushdelimbing.club lilacs after bl. Jun 03, While a young, healthy lilac bush thrives with virtually no maintenance, pruning it each year after it blooms helps ensure a gorgeous array of new blooms the following spring.
Maximize blooms by removing the old flowers, along with some new shoots, within the few weeks after the flowers. 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.
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.