Jooni

An exemplary photo of a Syringa bonsai

Syringa

1 Species

Species

Syringa vulgaris

Lilac (Syringa), most often common lilac (Syringa vulgaris) or the compact Meyer lilac (Syringa meyeri), is a deciduous flowering shrub grown as bonsai for its fragrant spring flowers in shades of purple, pink and white. It is a very hardy outdoor tree and needs a cold winter to set flowers.

A lilac bonsai suits growers with some experience: common lilac has fairly large leaves and only flowers well when pruned at the right time, although the tree itself is tough and vigorous. Meyer lilac, with smaller leaves and denser growth, is easier to keep in proportion. Lilac is not considered toxic to people or pets.

At a glance Syringa vulgaris

Difficulty
Intermediate
Placement
Outdoors
Light
Full sun
Watering
Moderate
Min. temperature
-10°C (14°F)
Foliage
Deciduous

Fertilizing

Feed from spring until late summer with a balanced slow-release fertilizer, or with liquid fertilizer every 2 weeks at half strength. In late summer, switch to a fertilizer lower in nitrogen and richer in phosphorus and potassium to support next year's flower buds.

  • Too much nitrogen gives long shoots, large leaves and few flowers.
  • Stop feeding in autumn and winter.

Placement

Lilac needs full sun, at least 6 hours a day, to flower well. In very hot summers, light afternoon shade protects small pots, and good air circulation reduces powdery mildew.

The species is very frost-hardy and needs winter cold to flower, so keep it outdoors all year. Roots in a pot are more exposed than in the ground, so protect the pot below -10°C (14°F) in a cold frame or unheated shed.

Pruning

Prune straight after flowering. Lilac forms next year's flower buds at the tips of this summer's shoots, so any pruning from midsummer onwards removes them.

  • After flowering, cut off the faded flower clusters and shorten shoots to two or three pairs of leaves.
  • Remove dead, weak or crossing branches and thin crowded areas to let in light and air.
  • Remove suckers from the base of the trunk regularly.

Hard structural pruning can be done in late winter, at the cost of that spring's flowers. Wire young shoots in late spring or early summer, as older branches are stiff and brittle.

Repotting

Repot young trees every 1-2 years and mature trees every 2-3 years, in early spring before the buds open or straight after flowering. Lilac roots vigorously and produces suckers, so regular root work keeps it in check.

  • Use a free-draining mix, such as 2 parts akadama to 1 part pumice, or equal parts leaf mould, bark, loam and sharp sand.
  • Lilac prefers neutral to slightly alkaline soil (pH 6.5-7.5).
  • Remove root suckers while repotting, and expect fewer flowers that year if you repot in spring.

Watering

Keep the soil evenly moist and let the surface dry slightly between waterings, but never let the root ball dry out completely. Lilac is sensitive to both drought and waterlogging, especially while the flower buds open and during flowering.

  • Check the soil daily in summer, when small pots may need water every day.
  • In winter, water less and keep the soil just moist.

Seasonal care

  • Spring: Enjoy the flowers, then prune straight after they fade and repot if due. Start feeding as the leaves open.
  • Summer: Give full sun, water carefully and stop pruning by midsummer, as next year's flower buds are forming. Switch to a low-nitrogen fertilizer in late summer.
  • Autumn: Stop feeding and let the tree go dormant. Clear away fallen leaves to reduce mildew and blight next year.
  • Winter: Keep the tree outdoors, as it needs cold to flower, and protect the pot below -10°C (14°F). Water only when the soil starts to dry.

Common problems

Lilac is hardy and long-lived, but a few problems are common.

  • Powdery mildew: A white coating on the leaves, common in late summer with poor air circulation. Thin the canopy, keep the leaves dry and use a fungicide if needed.
  • Lilac blight: Black spots on leaves and young shoots, which wilt and die in cool, wet springs; it is caused by bacteria. Cut out affected shoots with clean tools and keep the foliage dry.
  • Lilac leafminer: Brown blotches and rolled leaves where small caterpillars feed inside. Remove affected leaves early and use an insecticide on heavy infestations.
  • No flowers: Usually caused by pruning too late, too little sun, too much nitrogen or a winter that was too warm. Prune right after flowering, give full sun and keep the tree outdoors through winter.