Technically to answer your question: flowering starts after 80-110 growing degree days, when specifically would depend on where you live.
Lilacs (Syringa) (sometimes called Pipe trees) are a genus of about 20 species of flowering plants in the family Oleaceae, native to Europe and Asia. Lilacs range in size from large shrubs to small trees, 2-10 m tall. The leaves are opposite, deciduous, and in most species simple and heart-shaped, but pinnate in a few species (e.g. S. laciniata, S. pinnatifolia). The flowers are produced in spring, each flower about 1 cm diameter, white, pale pink or more generally purple, with four petals. The flowers grow in large panicles, and in several species have a strong fragrance. Flowering starts after 80-110 growing degree days.
Lilacs are used as food plants by the larvae of some Lepidoptera species including Copper Underwing, Scalloped Oak and Svensson%26#039;s Copper Underwing.
When do lilacs bloom?
Mine have been blooming for about 3 weeks now.
Reply:In my area--zone 5 in N. Ohio--they bloom in early May.
Reply:Right now. I have some starting to bloom in the back yard. It smellswonderful!
Reply:Depends on where you live and what variety of lilac. Usually only a couple of weeks in early spring.
Reply:I%26#039;m in zone 4...early May... there are some varieties that will bloom a little throughout the growing season, one of them is Dwarf Korean Lilac...also, if you need to prune lilacs, be sure to do it within a week or 2 after the blooms are spent... lilacs set their next flowers about 2 weeks after the current ones are spent