The Japanese lilac is a deciduous tree-form lilac attractive enough to serve as a specimen. It has a moderate growth rate, an upright growing habit, and a rounded shape. It is a mid-size tree belonging to the olive family and grown for the panicles of white flowers that are 6 to 12 inches long, which it bears for about two weeks in early summer. Seeds follow the flowers and last through the winter, giving the plant (along with its graceful form and pretty bark) some visual interest for the winter.
The best time to plant a Japanese lilac tree is in the late winter or early spring. Late fall is also an acceptable planting time.
|Botanical Name||Syringa reticulata|
|Common Name||Japanese lilac tree, tree lilac|
|Mature Size||20-30 ft. tall, 15-20 ft. wide|
|Sun Exposure||Full sun, partial sun|
|Soil Type||Well-drained, with average moisture and average fertility|
|Soil pH||Neutral to slightly acidic|
|Flower Color||Creamy white|
|Hardiness Zones||3-7 (USDA)|
|Native Area||East Asia|
Japanese Lilac Care
The Japanese lilac is very different from the plant most people associate with the word "lilac," so it helps to familiarize yourself with it before you consider buying one. It is more resistant to powdery mildew disease than the common, shrub-form lilacs (Syringa vulgaris). With its superior resistance to powdery mildew disease, the tree's leaves add to its beauty. Though these lilac plants are resistant to powdery mildew disease, it's still a good idea to space them far enough so that they have good air circulation.
You will be most happy with a Japanese lilac tree if you grow it in full sun. It will survive if grown in partial sun, but it won't produce as many flowers.
Since it needs well-drained soil, mix compost into the ground when you plant Japanese lilac trees. The compost will loosen the soil, promoting proper moisture flow. This is particularly important in clay-rich soils.
Keep the ground evenly moist, but make sure it drains well. Mulch will help with water retention. So will compost. Suitable water retention means you won't have to water the plant as often.
While a Japanese lilac tree can live in soil of average fertility, it does better in more fertile soil. Feed the plant by mixing soil amendments into the ground every spring. Buy a balanced fertilizer if you feel an extra boost is needed. Make sure to follow instructions on the bag carefully since over-feeding can burn the plant. After applying the fertilizer every spring, hose down the soil so that the fertilizer goes down to the roots.
Japanese Lilac Varieties
Tree-form lilacs come in three subspecies, having subtle differences from one another (such as the Chinese being a bit smaller, etc.):
- Japanese lilac tree (Syringa reticulata subsp. reticulata)
- Chinese lilac tree (Syringa reticulata subsp. pekinensis)
- Amur lilac tree (Syringa reticulata subsp. amurensis)
Cultivars are also available. The cultivars generally bear more blooms than the species plant and, for this reason, may be preferred over the latter. Cultivars include:
- 'Summer Snow': A smaller tree (20 feet high), this plant is even more tolerant of pollution than the species plant, making it an excellent street tree.
- 'Chantilly Lace': This is one of a few choices available with variegated foliage. In this case, the leaves bear creamy yellow margins. It grows to 20 to 30 feet high and 15 to 25 feet wide. Partial sun is better for this type.
- 'Ivory Silk': This is the most popular cultivar. At a maximum height of 25 feet, it stays a little shorter than the species plant. It begins blooming at an early age, and it bears many panicles.
- 'Signature': Gardeners truly interested in a continual sequence of blooms love 'Signature' because its panicles, although smaller than those on 'Ivory Silk,' come out a week or two later. Grow both to extend the bloom period.
- 'Ivory Pillar': This Japanese tree lilac sports a columnar form (25 feet high and 15 feet wide).
Comparison of Tree Lilacs and Common Lilacs
While common lilac shrubs and Japanese lilac trees belong to the same genus (Syringa), there are important differences between them, beyond the fact that you can more easily train the latter into tree form.
- Flower scent: Common lilacs have one of the plant world's most fragrant blooms, but many people feel that tree lilacs have flowers that smell overly sweet. The smell is often compared to the pungent smell of the flowers of privet shrubs (Ligustrum).
- Bloom time: A Japanese lilac tree flowers a bit later, giving you color in early summer (rather than late spring). This fact is useful as you plan out the sequence of blooms in your garden.
- Bark: The Japanese lilac tree's bark is a pretty brown, studded with lighter lines (called "lenticels"), as on cherry trees, whereas the common lilac's bark is an uninspiring gray.
Perform maintenance pruning on a Japanese lilac tree as you would on any tree or shrub. This means removing damaged, dead, and diseased limbs as soon as you find them, thereby reducing the chances that your plant will experience severe pest or disease infestations. Also, occasionally prune out some of the limbs from within the canopy of mature trees to improve air circulation. Focus on removing any branches that are crossing and/or rubbing against each other.
Beyond this maintenance pruning, Syringa reticulata often needs help in achieving the classic tree form. If left to its own devices, it will sometimes become multi-branched, rather than growing with a single trunk. To this end, prune off low branches each year in early spring until you expose as much trunk as you desire. Such pruning is especially important in the early years when you are training your plant to become a tree.