The Japanese lilac tree's huge flower clusters are showy but most people find the fragrance not very pleasant.
Japanese tree lilac is a large shrub or (more commonly) a small tree, cone shaped, and getting up to 30 ft (9 m) tall and 20 ft (6 m) wide. The deciduous leaves are opposite, 3-6 in (8-15 cm) long, and oval to broadly heart shaped with pointed tips. They are dark shiny green, sometimes turning dull yellowish brown before falling in autumn. In summer Japanese tree lilac bears large showy panicles of fragrant creamy white flowers. Some compare the fragrance to that of Japanese privet (Ligustrum japonicum) blossoms, not necessarily a compliment. The flower clusters are 6-12 in (15-30 cm) long and composed of many tiny tube shaped blossoms. Fruits are small, dry leathery capsules that turn brownish yellow in late summer. The bark is shiny purplish brown and smooth when young, flaking in curled patches on older specimens. Small stems and twigs are hollow.
Cultivars of Japanese tree lilac include the popular ‘Ivory Silk’ which is smaller than the species, just 10-12 ft (3-4 m) tall and 6 ft (2 m) wide, and blooms when young in its second or third year of growth. ‘Summer Snow’ is a compact, rounded shrub to 20 ft (6 m) tall that produces abundant flower clusters. ‘Miss Kim’ is later blooming with pale lilac flowers and leaves that turn purple in autumn. ‘Chantilly Lace’ has leaves with yellow margins. Peking lilac (Syringa reticulata subsp. pekinensis) is a rangy, spreading shrub with arching branches.
Location Syringa reticulata occurs in Japan. The subspecies pekinensis is from Mongolia and northern China.
Culture Light: Japanese tree lilac should be planted where it will get full sun. Moisture: Grow tree lilac in well drained fertile, humus rich, neutral to slightly alkaline to slightly acidic soil. They like their soil moist and appreciate being watered during prolonged dry spells. Hardiness: USDA Zones 3 7. Japanese tree lilac is not suited for warm climates, and does best where the winters are cold. It needs to experience a few frosts before it will bloom.
Propagation: Seed can be sown as soon as ripe. Young, fast growing stem tips can be rooted under mist. Cultivars of Japanese tree lilac are propagated commercially by bud grafting on seedlings and sometimes on Ligustrum root stock.
Japanese lilac trees bloom in early spring.
Japanese tree lilac is covered with cone shaped clusters of creamy white flowers for two or three weeks in early and midsummer It makes a fine stand-alone specimen or addition to an informal mixed shrub border. A group of three tree lilacs in bloom might be too much to handle! The purple-brown bark is attractive in winter. Japanese tree lilac is used as a street tree in northern cities in Asia, Europe and North America. The flower clusters are used in cut flower arrangements. Like the common lilac (Syringa vulgaris), the showy Japanese tree lilac is robust and non-demanding, often persisting in landscapes after the gardener has stopped gardening.
Japanese tree lilac is probably the easiest of the lilacs to grow. Like other lilacs, Japanese tree lilac tends to flower its most every other year. However, if flower clusters are removed before the fruits and seeds develop in late summer, the plant will bloom at peak levels again the following year. Young plants should be pruned to a single leader (thinning cuts) if a tree form is desired. For a wider growing, bushy shrub, cut the central leader back (heading cut) to encourage branching. See Floridata’s primer on pruning for how to make these specialized pruning cuts.