Mike Klahr, Ph.D. is the Boone County Extension Agent for Horticulture for the University of Kentucky Cooperative Extension Service.
 

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Japanese Tree Lilac
by Mike Klahr - posted 07/22/11


Some lighter colored evergreens at the base help show off the dark green leaves and white flowers of Japanese tree lilac.

If you saw a single-stemmed, creamy-white flowered tree blooming in late May, would you suspect that it was a lilac? Maybe not, but if the plant was a Japanese tree lilac (Syringa reticulata), that’s just what you would see.

Reaching heights of 20 to 30 feet, this tree-version of a lilac stands tall in many other ways when compared to the old-fashioned common lilac. For starters, the extremely showy flowers are presented several weeks later than the common lilac, extending the spring blooming season into late spring or early summer. Some years it even flowers into June. The slightly fragrant flower panicles are extremely showy, up to 12 inches long. Not only that, but the Japanese tree lilac is nearly pest free, being much more resistant than common lilac to problems such as powdery mildew, scale and lilac borer.

Michael A. Dirr, author of “Manual of Woody Landscape Plants: Their Identification, Ornamental Characteristics, Culture, Propagation and Uses,” has proclaimed this tree to be “the most trouble-free lilac, and the toughest of the lilacs; an excellent specimen tree or street tree, good in groups or near large buildings,” and even calls it one of his favorites.

Although the flowers appear late enough to avoid spring frosts, the dark green leaves of this deciduous plant emerge quite early. The showy blooms are then presented for two weeks against the backdrop of the lovely foliage. Sometimes described as a large shrub or small tree with stiff, spreading branches and an oval to rounded crown, Japanese tree lilac eventually becomes a graceful, somewhat arching specimen, spreading to a width of 15 to 25 feet.

In winter, the bark on young plants will make people think you have a cherry tree, since it is definitely cherry-like in appearance with a glossy reddish-brown color and marked with prominent horizontal lenticels just like many of the flowering cherries. Of course, even in winter, you can tell the difference just by looking at the small twigs. Lilacs always have opposite buds (directly across from each other), while cherry buds always have an alternate arrangement on the twig (left-right-left). As the lilac tree ages, its bark becomes gray and scaly.

Hardy from Zones 3 to 7, this tree is suited for use throughout the Midwest, even though it is native to Japan. Tolerant of clay soils and a range of soil pH from 6.5 to 8.0, Japanese tree lilac flowers best in full sun conditions. Surprisingly, many people are still not familiar with this tree, although it was introduced into cultivation in 1876. Today, it is successfully grown throughout much of the United States. ‘Ivory Silk’, an extremely hardy cultivar introduced in Ontario, Canada, in 1975, is a popular, vigorous and sturdy, upright tree with a straight trunk. This cultivar is good for planting under utility lines or in planters.

The Japanese tree lilac is a beautiful, hardy flowering tree that is adaptable and easy to grow. It should be used more often in home landscapes, parks and street plantings.

 


The giant flower clusters of Japanese tree lilac can be nearly 1 foot across.

Common name:  Japanese tree lilac

Botanical Name:  Syringa reticulata

Varieties to look for: ‘Ivory Silk’, ‘Chantilly Lace’, ‘Summer Snow’, ‘Regent’ 

Color: Flowers are a creamy white

Blooming period: May to June

Size: 20 to 30 feet tall, 15 to 25 feet wide

Exposure: Full sun

When to plant: Early spring

How to plant: Choose a balled-and-burlapped or containerized plant; dig a wide hole the depth of the rootball

Soil: Loam or clay

Watering: 1 inch per week during growing season

When to prune: Immediately after blooms fade

When to fertilize: Late fall or early spring, based on soil test results

Other maintenance: Apply a 2- to 3-inch layer of organic mulch in late spring

In your landscape: Great for use as a specimen tree, street tree, under utility lines, near large buildings, in planters or in group plantings

 

(Photos by Mike Klahr.  Story from Kentucky Gardener Volume III Issue IV.)

 

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