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Archive for Thursday, June 20, 2013

Garden Calendar: Tree lilacs add color to summer landscape

June 20, 2013

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When I think of lilacs, I usually think of fragrant, pale-purple blossoms that are a harbinger of spring.

But a different kind of lilac is earning a place in the Midwest landscape and my memory bank, and they are blooming in downtown Lawrence right now. This lilac is the Japanese tree lilac (Syringa reticulata), a small tree that produces large, creamy white panicles on the tips of its vase-shaped crown and bears little resemblance to its purple shrubby cousins.

The Japanese tree lilac, seen here in a planter in downtown Lawrence, is a small tree that produces large, creamy white panicles on the tips of its vase-shaped crown and are blooming in time for summer.

The Japanese tree lilac, seen here in a planter in downtown Lawrence, is a small tree that produces large, creamy white panicles on the tips of its vase-shaped crown and are blooming in time for summer.

Japanese tree lilac is native to eastern Asia, northern Japan, northern China, Korea and southeastern Russia, and is well-suited to the northeast Kansas climate. The tree is rated in USDA Cold Hardiness Zone 3, so it can handle much lower winter temperatures than we typically experience in Douglas County (rated as Zone 6). Japanese tree lilacs are generally not recommended for planting in Zone 7 or warmer climates.

Besides the showy flowers that appear when few other trees are blooming, Japanese tree lilacs have reddish-brown bark that peels back from the trunk in an ornamental fashion. They are also resistant to most pest problems, and only occasionally suffer from bouts of the powdery mildew that plagues most shrub forms of lilac. Borers are also an occasional problem when the tree is planted in a location that is unsuitable because of poor soil conditions or moisture issues.

​Japanese tree lilac is very fragrant, but the scent is quite different from shrub lilacs. Some people love it, while others find it reminiscent of mildew. If you have a sensitive nose, you might wish to visit a tree lilac in bloom and decide for yourself if the fragrance is enjoyable.

The blooms typically last a few weeks before turning into a cluster of attractive brown capsules. Pruning the clusters from the tree can encourage more prolific flowering in the following year, but it is unnecessary for plant health.

​The Japanese tree lilacs in downtown Lawrence and in some of the parks and landscaped right-of-ways are a variety called Ivory Silk. This variety grows to about 20 feet tall and 15 feet wide and has reddish-brown, exfoliating bark. The biggest difference between Ivory Silk and the species is the flower size. Ivory Silk’s flowers are larger and showier than that of the species. Ivory Silk is also a little smaller — the species is typically closer to 30 feet at maturity and can grow to greater sizes in the right environment.

​Another variety of Japanese tree lilac is called Summer Snow (Syringa reticulata subsp. pekinensis). Summer Snow is the same size as Ivory Silk, but its blossoms have a more buttery hue. Summer Snow is slightly more susceptible to disease and insect problems than other tree lilacs.

​Amur tree lilac (Syringa reticulata subsp. amurensis, previously mandshurica) is closely related to the Japanese tree lilacs. Amur lilac is much smaller than the other tree lilacs, only reaching 6 to 8 feet high by 4 to 6 feet wide at maturity. It also prefers to grow in a multi-stemmed clump rather than from a single trunk, but it is still more tree-like than the shrubby cousins.

Japanese tree lilacs are also fairly drought tolerant.

— Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. Contact her or an Extension Master Gardener with your gardening questions at 843-7058.

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