Q. Recently I have seen trees around town that were beautiful. They have gorgeous sprays of white flowers, which I found unusual for this time of year. What kind of trees are they? Are they good to use in my landscape?
A. The trees in question were probably Japanese Tree lilacs. Although a lilac, this member of the olive family is quite different in appearance from the shrub lilacs most of us are familiar with.
The genus Syringa (lilacs) has about 30 species of trees and shrubs native to Europe and Asia. Japanese tree lilac is the only species that attains a tree-like form. Japanese tree lilac was introduced into cultivation in 1876.
The tree lilac is native to northern Japan. Plants are commonly found growing on limestone cliffs. Tree lilacs are small to mid-sized trees, reaching a height of about 20 to 30 feet, with a 15-foot spread. The huge clusters of creamy white flowers, borne in early summer for about two weeks, are the main ornamental feature of the tree, but they lack the perfume fragrance of the spring-blooming lilacs.
Tree lilacs are being used more frequently as a street tree in some parts of the country. They tend to be quite hardy to cold and tougher environmental conditions; they are salt-tolerant; and their small stature makes them a good candidate for spaces near power lines.
Japanese tree lilac is also popular as a garden specimen, as an accent in a shrub border, and for providing shade and a colorful early summer show for a deck or patio area.
The tree is often sold as a multi-stemmed specimen or as a single-trunked tree. Several cultivars exist:
Ivory Silk is cold hardy to USDA hardiness zone 3. It has an upright oval form. Ivory Silk won the Cary Award in 2006 for outstanding plant for New England gardens.
Summer Snow is also cold hardy, with a compact upright rounded form and persistent seed pods.
Morton – trademarked as China Snow – is from the Chicagoland Grows program and is noted for its tolerance of drought, extreme cold and de-icing salts, as well as its narrow habit and attractive, cherry-like bark.
Summer Charm bears profuse white blooms similar to those of Ivory Silk. However, its lustrous dark green foliage is finer textured than that of Ivory Silk and has a more rounded, relaxed form.
If properly located on an appropriate site, healthy, well-maintained trees will have few problems. However, lilac borer can be a problem for stressed trees. The larvae tunnel in the branches, causing wilting, particularly on drought-stressed trees. Severely infested branches may break off.
Plants in partial shade can be infected with powdery mildew, common with many lilacs, which can cause some defoliation. Even though tree lilac is not a native tree, cardinals, chickadees and finches have been observed eating the seeds.
This distinctive tree can be a good choice for small spaces to prolong the flowering season and provide more interest in home and urban landscapes.