The best time for pruning lilac bushes is right after their flowering has ceased. If you are pruning lilac trees or shrubs entirely to within inches of the ground, it is best to do so in early spring.
New shoots will develop during the regular growing season as long as there are a few healthy shoots left. 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.
Jul 08, Most flowering shrubs need regular pruning to keep them vibrant, and the common lilac (Syringa vulgaris) is no exception. Lilac bushes will typically flower without any effort from you. However, if left to grow and spread on their own, common lilacs will eventually only flower on the tops of the uppermost branches.
Rather, prune each major branch back to a side shoot. Remember, as with pruning any shrubs or trees, the shoot or bud just below where you prune will grow out in the direction it is pointing.
If you don’t want a shoot there, perhaps blocking a walk or path, prune elsewhere.