Japanese Tree Lilac (Syringa reticulata)

The Japanese tree lilac is a fragrant flowering tree native to northern China that is perfect for the garden or street. With full sun and moderate water, its masses of small blooms will appear in early summer and emit a pleasant scent. Though the japanese tree lilac is relatively hardy on the whole, the flowers are susceptible to late frosts.

I. Appearance and Characteristics 

Syringa reticulata, the Japanese tree lilac, is a species of flowering plant in the family Oleaceae native to eastern Asia, which is grown as an ornamental in Europe and North America.

It is a deciduous small tree growing to a height of 12 m (39 ft), rarely to 15 m (49 ft), with a trunk up to 30 cm (12 in), rarely 40 cm (16 in) in diameter; it is the largest species of lilac, and the only one that regularly makes a small tree rather than a shrub. The leaves are elliptic-acute, 2.5–15 cm (0.98–5.91 in) long and 1–8 cm (0.39–3.15 in) broad, with an entire margin, and a roughish texture with slightly impressed veins. The flowers are white or creamy-white, the corolla with a tubular base 0.16–0.24″ (4–6 mm) long and a four-lobed apex 0.12–0.24″ (3–6 mm) across, and a strong fragrance; they are produced in broad panicles 5–30 cm (2.0–11.8 in) long and 3–20 cm (1.2–7.9 in) broad in early summer. The fruit is a dry, smooth brown capsule (15–25 mm long), splitting in two to release the two winged seeds.

II. How to Grow and Care

Sunlight

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.

Watering

Japanese tree lilac thrives in moderately moist soil, mirroring its origins where it experiences distinct wet and dry seasons. It has adapted to tolerate some drought but flourishes when the relative humidity is higher. Watering should be moderated to once every three weeks, ensuring that the soil dries out slightly between waterings. As japanese tree lilac is more commonly grown outdoors, it benefits from a mulch layer which helps retain soil moisture and mimics the leaf litter of its natural setting, crucial for maintaining adequate hydration during its active growth cycle.

Soil

Japanese tree lilac can endure poor soil and adapts to various soil types, but it is sensitive to acidic soil. It prefers well-drained, loose, fertile soil which is neutral to alkaline (pH close to or higher than 7). It should not be planted in low-lying areas, because long-term accumulated water can cause poor growth and even death. If the soil in the garden is not fertile enough, add compost, bone fertilizer or other fertilizers.

Fertilizing

For Japanese tree lilac, utilize balanced nutrition fertilizers to boost health, flower proliferation, and vigor. Apply fertilizer annually in spring, before new growth starts. A slow-release formula, appropriate in quantity to manufacturer’s guidelines, is ideal. Avoid over-fertilization, which can harm Japanese tree lilac. Fertilization alters with growth phases; young Japanese tree lilac benefit from regular fertilizing, while mature ones require less. Apply evenly around the root zone and water deeply to integrate nutrients. Adherence to these practices ensures optimal results for Japanese tree lilac.

Planting Instructions

Select varieties with bloom time, color, and height you prefer. Japanese tree lilac can be transplanted after leaves fall off in the fall or after the soil is defrosted in spring. If transplanted in the fall, plants can form a root system before the next bloom season and perform well. Transplanting in spring can prevent the seedlings from freezing in the harsh winter and increase the survival rate. If transplanted in summer, leaf buds and flower buds grow quickly. However, excessive evaporation of the aboveground part may negatively affect its growth and blooms for the following year.

If you can buy two-year-old or older saplings from the nursery, they will blossom the same year or the following year. Ramets can be dug from mature Japanese tree lilac for transplanting. Care should be taken to ensure that the seedlings are at least 30 cm tall. It may take 3-4 years for these smaller seedlings to blossom.

When transplanting a seedling, dig a pit 5 to 8 cm larger than the earth ball and twice its diameter. Stretch the roots of the seedling out and put them into the pit. Cover the pit with soil mixed with compost. Water the pit when half the soil is filled in, then continue to fill in soil. The filled soil should be kept level with the ground. Also make sure that the top layer of the root system is several inches under the soil surface, so the root system is completely buried. Water thoroughly after planting, and then once every 10 days, 3-5 times in succession, for strong root establishment. Depending on the variety, space the plants 1.5 to 4.5 m apart.

Pruning

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.

Propagation

Japanese lilac trees can be propagated from cuttings taken in the late spring or early summer. Once the cutting is planted in the soil, it should take root in about six weeks. Here’s how:

• Select a healthy branch, and use pruning shears to cut a 4 to 6-inch leafy cutting. Make sure to cut it at a 45-degree angle when taking the cutting from the branch.
• Dip the cut edge into a root hormone powder formulated for softwoods.
• Prepare a 10-inch container with drainage holes, with potting soil, and make a 2-inch deep hole with your finger in the center of the soil.
• Put the cutting, with the cut edge down, in the hole, and press the soil down around the cutting.
• Water the pot until the soil is evenly moist. Do not over-wet.
• Place the potted cutting in partial or dappled sun and keep the soil damp during the rooting period.

How to Get to Bloom

These trees love to show off their fragrant flowers in the late spring and early summer. To get the most blooms from the Japanese lilac tree, plant in full sun and do maintenance pruning. The flowers will last about two weeks and then produce green-colored clusters, which turn into yellow seed capsules that last during the cool months. Songbirds enjoy feasting on the seed capsules.

III. Harvesting and Storage

Blooms can be used as excellent fragrant cut flowers with a vase life of 3-5 days. Cut off the stalks and insert them into the vase when about 1/3-1/2 of the flower buds bloom. Cut at the bases of the branches with sharp scissors, not broken by hand. Japanese tree lilac can produce many flowers each spring. However, don’t cut too many stalks from a sapling blooming for the first time; otherwise, it will impact the growth of the sapling.

You can also dry Japanese tree lilac flowers. Tie the fresh stalks into a bunch with a rope, and hang them upside down in a dry, airy place for 1-3 weeks. After the flowers are completely dry, take them off gently and appreciate them as dried flowers.

IV. Types of Japanese Lilac Tree

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).