The Best Time to Prune a Lilac Tree
The best time to prune a lilac tree is immediately after flowering. Prune back to a branching limb or 2-3 inches above the ground.
Prune A Japanese Lilac Tree
The Japanese lilac tree--scientifically known as Syringa reticulata--is a large ornamental multi-stemmed shrub that features a vase-shaped crown, spreading branches, oval, dark green leaves, and profuse, showy flowers of creamy white, borne on large panicles. By using the proper pruning techniques, you can encourage shapely and vigorous growth, promote flowering, and make your Japanese lilac tree more resistant to pests and diseases. Prune the flowers from your Japanese lilac tree as soon as they are spent. Perform a rejuvenation pruning on mature Japanese lilac trees every few years by cutting one-third of the large, old stems all the way back to the ground in late winter. The following year, again in late winter, remove half of the old stems.