Lilacs are hardy perennial flowering plants of the genus Syringa, in the olive family Oleaceae. Broader botanical consensus identifies about 20 to 30 species, some subspecies, defined by geographical original territories, and many cultivated hybrids. Their natural habitat includes woodland and scrub across a range of altitudes distributed across Eurasia, with the centre of diversity in East Asia, and are now naturalized in many temperate, and colder climates of the world.
There are more than 2000 named lilac cultivars, some dating back to the 1800s.
They come in:
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seven colour classifications; white, pink, violet, blue, magenta, lilac and purple, with variations.
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a range of heights, S. reticulata can grow up to 18 m tall, other lilac species grow into a large bush or spread to form dense thickets via asexual reproduction. Lilacs can be purposed in foundations, borders, tall privacy hedges and as specimen plants grown as focal points in the landscape.
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bloom sizes ranging from 4cm to 30cm+ panicles on long, stout stems that make excellent cut flowers.
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various blooming periods, where when planted together they provide a longer season of colour and scent that extends over weeks each spring.
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different flower forms.
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diverse aromatic profiles, ranging from heavily scented to faint or even nonexistent smell. The older dark purple heirloom lilacs often offer the most intense perfume while white lilacs are more softly scented. Variety wise, the common lilac has the strongest, classic lilac smell, French hybrid lilacs can be very fragrant or have a very light smell, early Korean lilacs have a more subdued aroma and tree lilacs possess a differing, pungent fragrance. The fragrance of lilacs is heavily influenced by weather, smelling strongest on warm, sunny days and faint or absent in cold or damp conditions. Lilac flowers are edible and have culinary, medicinal and cosmetic uses.
Recognized lilac species:
Syringa emodi, the Himalayan lilac is a robust shrub that grows 5m tall and spreads 4m wide. The vigorous branches bear upright panicles of scented purple, pale lilac or white flowers in early summer. Their natural growing range is found on the highlands of Central Asia and where they grow on slopes at 2000m to 3000m altitude.
Syringa josikaea, the Hungarian lilac, or Lady Josika's lilac is a large shrub with a very restricted range in Europe. The deciduous shrubs grows 2m to 4m tall with strongly fragrant dark pink flowers produced in slender panicles. This species demonstrates vigorous clonal reproduction, which seems to predominate over sexual reproduction. The fully frost hardy plant allows for cool to temperate climate growing conditions, including oceanic extremes and the northern arctic, and also grows in full sun to semi shade.
Syringa komarowii, the nodding lilac, indigenous to central China, is a shrub growing to 3m to 6m with erect branches on which panicles that often hang limply are borne. The fragrant flowers range from pink to mauve in colour, sometimes with a white base. The blooms are produced in early summer, rather later than most other cultivars and attract bees, butterflies and birds. This species needs to be planted in full sun, like most lilacs and is able to survive cold winters. The flowers are good for cutting and the plant is used for breeding with other species of Syringa.
Syringa oblata, the early blooming lilac or broadleaf lilac is the most commonly seen lilac species in China. The 3.5m to 5m tall shrubs or small trees inhabit gravelly mountains, roadsides, stream banks, thickets, valleys, and woods at 100m to 2600m altitudes. The fragrant flowers range from purple to lilac, occasionally white, in colour borne in lateral, congested, lax or erect panicles that appear earlier than any other species of Syringa.
Subspecies:
Syringa oblata subsp. dilatata, the Korean early lilac.
Syringa pinetorum grows in valleys under pines at altitudes of 2200m to 3600m in China and is not yet known in cultivation. The 1m to 3m tall and wide shrub bears lateral, erect and loose panicles of pale red or lilac flowers in early summer.
Syringa pinnatifolia, the pinnate lilac, native to Western China, is an open, upright, deciduous, 2.5m to 4m tall shrub, that mostly grows in a temperate biome, surviving at altitudes up to 9000 ft and bear panicles of fragrant, lilac to pink flushed, white flowers in early summer. The leaves are unusually pinnate.
Syringa pubescens, the hairy lilac, native to Korea and China, is a substantial deciduous shrub reaching 6m tall and wide, and bears panicles of heavily scented, white throated lilac flowers in early summer.
Subspecies:
Syringa pubescens subsp. julianae.
Syringa pubescens subsp. microphylla.
Syringa pubescens subsp. patula, also called Syringa velutina, Korean lilac, Manchurian lilac or Miss Kim lilac.
Syringa reticulata, the Japanese tree lilac, native to eastern Asia, is the largest species of lilac and the only one that regularly makes a small tree rather than a shrub. The deciduous small tree grows to a height of 12m, sometimes 15m, and, in early summer, produces white or creamy white flowers with a strong fragrance in broad panicles.
Subspecies:
Syringa reticulata subsp. reticulata, also called Syringa japonica, S. amurensis var japonica or Ligustrina japonica.
Syringa reticulata subsp. amurensis, also called S. reticulata var. mandschurica.
Syringa reticulata subsp. pekinensis, the Pekin lilac or the Chinese tree lilac.
Syringa tomentella, native to China, reaches up to 1.5m to 7m tall and wide at maturity. The white to pink, or lilac red flowers are sweetly scented and appear in summer. The shrub, introduced into cultivation in 1904, can be found in the wild on woodland slopes, in valley thickets and along gullies, at 2500m to 3600m altitude.
Syringa villosa, the villous lilac or late lilac is a shrub that grows up to 4m tall. The red, white, pink or purple flowers are long and highly fragrant, and appear in early summer.
Subspecies:
Syringa villosa subsp. villosa.
Syringa villosa subsp. wolfii.
Syringa vulgaris, the lilac or common lilac, native to the Balkan Peninsula, grows into a large deciduous shrub or multi stemmed small tree, up to 7m tall, and produces secondary shoots from the base or roots, which in the course of decades may produce a small clonal thicket. The scented flowers, arranged in dense, terminal panicles, are usually lilac to mauve, occasionally white in colour, that appear in early summer, before many summer flowers come into bloom. Many hybrid cultivars have been bred from the fast growing Syringa vulgaris, including the doubled flowered French lilacs.
Syringa meyeri, the Meyer lilac or Korean lilac is a smaller, slow growing, disease resistant lilac with pink to pale purple flowers. The heavy bloomer flowers at a very young age.
Hybrids:
S. × chinensis (S. vulgaris × S. persica), the Chinese lilac or Rouen lilac.
S. × diversifolia (S. oblata × S. pinnatifolia), the varyleaf lilac, is a relatively early lilac.
S. × henryi (S. josikaea × S. villosa).
S. × hyacinthiflora (S. oblata × S. vulgaris).
S. × josiflexa (S. josikaea × S. komarowii).
S. × laciniata (S. protolaciniata × S. vulgaris), the cut leaf lilac, a lilac hybrid of old origin.
S. × persica L., syn Syringa protolaciniata , the Persian lilac prefers the warmer winters of USDA zones 5 to 9.
S. × prestoniae (S. komarowii × S. villosa).
S. × swegiflexa (S. komarowii × S. sweginzowii).
S. x prestoniae (S. villosa x S. reflexa), the Preston hybrid lilacs are later blooming lilacs developed in Canada.
Lilac wood is a relatively hard wood, with an estimated Janka hardness of 2 350 lbf /10 440 N, good for woodturning. The heartwood can have various streaks of brown and purple.
When do lilac plants blossom?
Lilacs reliably set flower every year in spring and early summer, and the remontant Bloomerang® series offer a large initial spring bloom followed by a rest period then reblooming mid summer until the first fall frost.
How to prune lilac plants to get more flowers, promote new growth and rectify leggy growth?
- Lilacs flower profusely, originating in pairs from the terminal buds, and will produce more flowers the following year if the flower clusters are promptly pruned off, or deadheaded, as they begin to dry up, after the colour has faded and before seeds form.
- Lilacs flower on old wood, or growth from the previous year, and develop next year's buds shortly after blooming in the spring. Pruning in late summer, autumn, winter or early spring removes the new flower buds. Prune at the same time that the spent blooms are removed, within a couple weeks after the plant flowers.
- Lilacs bloom best on younger growth, flower panicles can be sparse if the lilac plant consists primarily of aged wood, twiggy growth on shoots that have flowered more than once or twice can be cut to a strong, outward growing side shoot.
- To fix leggy lilac bushes, remove 1/3 of the oldest, thickest canes at ground level each year for three consecutive years.
- A heavily overgrown lilac bush can be rejuvenated with a hard, severe pruning back to half a foot from the ground. The plant will grow back to full, consistent flowering in 1 to 3 years.
Optimal growing conditions:
- Lilac plants thrive in full sun but can tolerate light shade.
- Lilacs are exceptionally cold tolerant, they are hardy to USDA zones 3 to 7, although some varieties grow in zone 2, others in zones 8 and 9.
- Protection from localized harsh, strong bitter cold winds, which can damage their flower buds and break stems, can be advantageous.
- Lilacs benefit from good air circulation, especially to control powdery mildew, a common lilac disease.
- Plant lilacs in well draining, fertile grounds.
- Lilacs grow best in neutral to slightly alkaline, sweet soils at pH 7.0 to 8.0.
- Lilacs are drought tolerant plants once established.
- Lilacs do benefit from lightly moist and organic rich soils, let amassed leaves accumulate at their base to form mulch and provide composted nutrients independently.
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An excess of nitrogen and too little light will limit blossoming.
How to propagate lilacs:
- Lilac flower panicles mature into clusters of brown capsules that split to release two winged seeds. The harvested dried seed pods need to be cold stratified to germinate. Follow the natural weather cycle, cold stratify the seeds outdoors or artificially indoors for 6 to 8 weeks. Germination usually occurs in 14 to 60 days at 16ºC to 21ºC. The seedling may not grow to be identical to the parent plant and should bloom in 3 to 5 years.
- Lilacs plants spread in their immediate vicinity through vegetative reproduction. The adventitious shoots can be removed and transplanted as a means of propagation. Divide in late spring to early summer to give the shoot enough time to become established in its new environment before cold weather sets in.
- Other methods include rooting cuttings, grafting and air layering.
Lilac seed pod clusters provide food for birds and small mammals along with winter interest in the garden. In the summer, lilacs are food plants for the larvae of several moth species, the night pollinators, who also find shelter among the branches as adults, and the nectar rich flowers provide essential nutrients and amino acids to native bees, butterflies, moths and hummingbirds.
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