Syringa, commonly called lilac forms buds in spring. Lilacs flower on second year's wood. This means that shortly after the lilac flowers in late spring, the following year's flower buds start to form. Pruning to avoid loss of the following years' flowers ideally takes place immediately after flowering (within two weeks after the flowers fade). Pruning now will remove those buds. There many lilac varieties, an easy care lilac is Syringa reticulata are wonderful disease- and pest-resistant plants which can grow up to 20 feet tall. They have creamy-white flowers that appear in late June.

More from our library guides (Mertz library's Plant Info Service) http://libguides.nybg.org/troublefreelilacs

Hope this is helpful.