Everything 10 minutes down the highway from me is a month.
Iowa State University Extension.
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). Pruning in early spring will also cut off some of that season’s flowers. Broken branches of course should be pruned off whenever seen.
Just be sure if pruning after bloom to not prune past mid-summer. This will allow time for the wounds to heal before winter, and any new growth that might be stimulated should harden properly before shrubfalling.clubg: Chesapeake VA. May 20, Pruning in the winter will remove all the bloom for the following spring.
If your lilac is very thin and lanky, renovate it by removing the oldest branches gradually over two or three consecutive seasons, always in the late spring.
The first spring, remove about one-third of the old canes all the way down to the shrubfalling.clubg: Chesapeake VA. 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 shrubfalling.clubg: Chesapeake VA. Jul 14, Trim mature lilac bushes so that they remain within 6 to 8 feet.
Left on their stems, the flowers will die but continue sapping energy that could be spent on new growth.
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 shrubfalling.clubg: Chesapeake VA. Monitor the miniature lilac in the spring. Prune the plant right after the flowers die so as not to sacrifice the buds that will develop into next year’s blossoms.
2 Deadhead spent blossoms by Missing: Chesapeake VA.