Japanese Lilac Tree Profile

Japanese lilac tree in bloom.

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The Japanese lilac is a deciduous, tree-form lilac. 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 that is grown for the panicles of white flowers it bears for about two weeks in early summer. It is very different from the plant most people associate with the word, "lilac," so familiarize yourself with it before you consider buying one.

Botanical Name

Syringa reticulata

Common Name

Japanese lilac tree, tree lilac

Plant Type Tree
Mature Size 20 to 30 feet tall and 15 to 20 feet wide
Sun Exposure

Full sun to partial sun

Soil Type

Well-drained, with average moisture and average fertility

Soil pH

Neutral to slightly acidic

Bloom Time June
Flower Color Creamy white

Hardiness Zones

3 to 7
Native Area East Asia
japanese lilac tree
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How to Grow Japanese Lilac Trees

The best time to plant Japanese lilac tree is in the late winter or early spring. Late fall is also an acceptable planting time. Although more resistant to powdery mildew disease than are the common, shrub-form lilacs (Syringa vulgaris), it is still a good idea to space them far enough so that they get good air circulation.

Light

You will be most happy with 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.

Soil

Since it needs a well-drained soil, mix compost into the ground when you plant Japanese lilac trees. The compost will loosen the soil, promoting moisture flow. This is particularly important in clayey soils.

Water

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.

Fertilizer

While Japanese lilac tree can live in soil of average fertility, it does better in more fertile soil. To feed the plant, mix soil amendments into the ground every spring. If you feel an extra boost is needed, buy a balanced fertilizer. Follow instructions on the bag carefully, since over-feeding can burn the plant. Apply the fertilizer every spring. Hose down the soil afterward so that the fertilizer goes down to the roots.

Pruning Japanese Lilac Trees

Perform maintenance pruning on 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.

Varieties of Japanese Lilac Trees:

The cultivars generally bear more blooms than the species plant; for this reason, alone, they would be preferred over the latter. Cultivars include:

  • 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 continuous sequence of bloom love Signature because its panicles, although smaller than those on Ivory Silk, come out a week or two later.
  • Ivory Pillar: This Japanese tree lilac sports a columnar form (25 feet tall 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 stink. The smell is often compared to the smell that the flowers of privet shrubs (Ligustrum) have.
  • Bloom time: 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 bloom in your garden.
  • Bark: Japanese lilac tree's bark is a pretty brown studded with lighter lines (called "lenticels"), as on cherry trees, whereas common lilac's bark is an uninspiring gray.

Landscape Uses for Japanese Lilac Trees

Because Japanese lilac tree bears panicles of flowers that are 6 to 12 inches long, it is attractive enough to serve as a specimen. 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. With its superior resistance to powdery mildew disease, its leaves add to its beauty.

It is small enough to grow near a deck or patio, and it lacks the kind of aggressive root system that is dangerous to plant around patios, walkways, driveways, and septic lines.