Persian lilac

Persian lilac: how do you recognise it?

Habit

Rounded, dense shrub about 2 m tall and as wide, with slender, slightly arching stems.

Leaves

Narrowly lance-shaped, 2–6 cm long, untoothed, in opposite pairs; dull green. They fall in autumn without notable colour.

Flowers

Loose panicles of 5–8 cm along the previous year’s stems, in May. Each flower is a small tube with four lobes.

Colour

Pale lilac; white in ‘Alba’.

Scent

Sweet, the classic lilac scent, strongest on a warm, still day.

Fruit

Rarely sets seed; the spent trusses turn brown and stay on until you cut them off.

Flowering: May · Plants: March–April and October–November · Pruning: June

Why grow it?

• A generous show in May, with fragrant lilac panicles all over the shrub.
• Smaller and finer than common lilac: it also fits a small garden or a mixed border.
• Bees and butterflies love its nectar.
• Flowering stems look lovely in a vase and scent the house.
• Tough and fully hardy, on sand, loam and clay.
• Even after flowering it is a calm green shrub with a graceful, arching shape.

Persian lilac: where does it grow best?

• Sun to partial shade; it flowers most freely in full sun.
• Any well-drained garden soil: sand, loam or clay. It tolerates acid to chalky soil, but prefers neutral to chalky.
• Moderately moist soil; not a spot where water stands.
• Allow 2 m; in an informal flowering hedge, plant 1–1.5 m apart.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

2 m tall, 2 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Peony: Flowers just afterwards and fills the border with large blooms.
• Ornamental onion: Purple globes in May, in the same colour range as the lilac.
• Hardy geranium: Low, flowering ground cover at the base.
• Columbine: Flowers at the same time and self-seeds freely between the shrubs.
• Late tulips: Colour at the base while it flowers in May.

Persian lilac: when and how to plant it?

Plant in March–April and October–November.

1. Plant in March–April or October–November, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and loosen the bottom.
3. Mix a few spadefuls of compost into the soil you dug out.
4. Set the shrub at the same depth as in the pot and firm the soil well.
5. Water in thoroughly straight away.
6. Spread a mulch of compost or wood chips around the base.

Care

Water

Regularly in dry spells during the first year. After that, only in long dry periods.

Feeding

In March, a spadeful of compost or some organic fertiliser. Too much nitrogen gives lots of leaves and few flowers.

Mulching

A layer of compost in spring keeps the soil moist and weed-free.

Spent flowers

Cut off the faded trusses straight after flowering, just above the first leaves. This keeps the shrub tidy.

Space

Give it room to show its arching shape; a lilac that is cut back hard every year flowers poorly.

Tip: Cut off the faded trusses straight after flowering and never prune later in summer or in winter: you would remove next year’s flower buds.

Persian lilac: when to prune it?

Pruning months: June.

When: In June, straight after flowering. It flowers on the previous year’s wood.

How:

• Cut the faded trusses back to just above the first leaves or new shoots.
• Remove dead, weak and crossing stems.
• Every few years, take out one or two of the oldest stems right at the base so that young stems can come through.
• An overgrown or bare shrub can be renewed over three years: each year after flowering, remove a third of the oldest stems at the base.

Caution: Do not prune later than July or in winter: in summer it already forms the flower buds for next year.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June: 10 cm cuttings from young, non-flowering shoots, lower leaves removed, in moist cutting compost under plastic. Keep them warm and moist until they root.

Layering

In spring, bend a low stem into the soil and peg it down; sever it a year later and replant it.

Persian lilac: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy to about −30 °C: no protection needed in Belgium.
• In winter the flower buds are already in place on the stems, so do not prune in winter.
• In a large pot: wrap the pot in hessian in hard frost so the roots do not freeze.

Diseases and pests

• Powdery mildew: White powder on the leaves in late summer. It looks unsightly but does little harm. Keep the shrub open and water in dry spells.
• Lilac leaf miner: Small caterpillars mine and roll the leaves, which then turn brown. Pick off affected leaves and put them in the household waste.
• Lilac blight: In a cold, wet spring, young shoots and flower buds can blacken and wilt because of a bacterium. Cut them back to healthy wood and clean your secateurs.
• Poor flowering: Usually caused by pruning in summer or winter, too much shade or too much fertiliser. From now on prune only straight after flowering.

Through the year

• March: Plant. Give compost.
• April: Plant. Mulch. The flower buds swell.
• May: Flowering: fragrant lilac panicles. Cut stems for the vase.
• June: Remove spent trusses and prune. Take softwood cuttings.
• July: Water in dry spells. No more pruning: the new flower buds are forming.
• August: Watch for powdery mildew. Water in dry spells.
• October: Plant.
• November: Plant. Clear fallen leaves if there was mildew.
• December: Rest. Do not prune: the flower buds are already in place.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Persian lilac is one of the parents of Rouen lilac (Syringa × chinensis), which arose in the 18th century in the botanic garden of Rouen from a cross with common lilac.
• Despite its name it is not known in the wild in Iran: it has been a garden plant there for a very long time.
• Lilacs belong to the olive family, along with privet, forsythia and jasmine.