Plant taxonomy classifies common lilac bushes as Syringa vulgaris. An example of a cultivar of this plant is 'Wedgewood Blue.' Mention of these plants almost surely does not evoke thoughts of the extra virgin olive oil you find so essential when you cook Italian meals, yet Syringa is, in fact, a member of the olive family, along with other such ornamental plants as ash trees, forsythia shrubs, and privet shrubs.
Most kinds are deciduous shrubs. 'Wedgewood Blue' is one variety that has a compact growth habit. But because of the height some varieties attain at maturity, people sometimes refer to them as "lilac trees," lumping them in with the other wonderful flowering trees of spring. These plants should not, however, be confused with the true "tree lilacs," that is, Japanese tree lilacs (Syringa reticulata) and Chinese tree lilacs (Syringa pekinensis).
True "tree lilacs" (Syringa reticulata and Syringa pekinensis) bloom a bit later than lilac bushes. Their blooms are white, and they are not as aromatic as the flowers of common lilac bushes. But the tree lilacs do have an attractive bark, especially the Chinese tree lilac, which has a shedding bark similar to that of the paper birch.
Profile of the Lilac Shrub
'Wedgewood Blue' attains a height at maturity of only 6 feet, with a spread equal to that. But the species plant can grow to be anywhere from eight to 20 feet high. Flower color for 'Wedgewood Blue' is lavender-blue, and the flowers are contained in thick clusters. But other types come in a variety of different colors such as white, burgundy, deep purple, and, of course, the namesake color, "lilac" (light purple).
Blooming time is late spring. The leaves are dark green, but this shrub is grown first and foremost for the fragrance of its flowers and their beauty, not its foliage. The smell of their blossoms is one of the most unforgettable aromas of the plant world.
It is beyond dispute that the outstanding quality of many of these plants is the smell of their flowers. However, not all types are equally fragrant; grow Syringa vulgaris when in doubt if the smell is your main interest. They are among the most fragrant flowers available to gardeners in cold climates.
Growing Tips: Planting, Care (Pruning, Etc.)
The climate is most favorable for growing these flowering shrubs in USDA plant hardiness zones three through seven. Grow lilac bushes in full sun. They prefer a rich, well-drained, loamy soil with a neutral soil pH, but they will still grow in clay soil (just not as well). These wonderful bushes are, unhappily, prone to powdery mildew disease, so provide good air circulation by keeping their branches pruned.
The right time to prune is just after blooming is over, since these are shrubs that bloom on old wood. Branch pruning is done to thin out the growth (for better air circulation) and to keep the height of the plants in check. In addition, cut the dead flowers off when they are done blooming. This will prevent the seed from forming and thereby promote more profuse flowering the next spring.
If your lilacs are not flowering, there are some tricks you can try. A frequent problem growers have with common lilacs is that they become too big as the years go by. This happens when you (or the prior landowner) have failed to stay ahead of their growth by pruning them. But the problem is fixable by trimming the overgrown lilacs, which will also help rejuvenate them.
Uses in Landscape Design
Common lilac bushes are attractive enough to be treated as specimens. They are also often planted in rows along property borders and pruned into loose hedges. Other kinds of lilac bushes exist, too, in addition to the common type covered above. The 'Miss Kim' cultivar is small enough for use in foundation plantings, as is the even more compact Bloomerang lilac, which is a dwarf shrub.