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At a glance
| Botanical name | Syringa vulgaris (common lilac) |
|---|---|
| Family | Oleaceae (olive family) |
| Type | Deciduous, multi-stemmed suckering shrub |
| USDA zones | 3–7 (needs cold winters) |
| Mature size | 8–15 ft tall, 6–12 ft wide |
| Bloom | Mid-spring, on last year's wood; fragrant |
| Light | Full sun (6+ hours) |
| Soil | Well-drained, near-neutral to slightly alkaline |
| Native range | Balkan Peninsula, southeastern Europe |
| Common problems | Powdery mildew, bacterial blight, lilac borer, scale |
What a lilac bush is
Common lilac is a large, upright, multi-stemmed shrub with heart-shaped leaves arranged in opposite pairs and dense, cone-shaped clusters of very fragrant flowers in purple, lilac, blue, pink, magenta or white. NC State Extension lists its origin as the Balkan Peninsula, and Missouri Botanical Garden as southeastern Europe. University of Minnesota Extension calls lilacs long-lived, and they spread slowly by suckers from the base.
Other lilacs worth knowing:
| Lilac | Size | Bloom | Why grow it |
|---|---|---|---|
| Common lilac (S. vulgaris) | 8–15 ft | Mid- to late spring | Classic fragrance; widest color range |
| Dwarf Korean lilac (S. meyeri 'Palibin') | 4–6 ft | Mid- to late spring | Small yards; resistant to powdery mildew; blooms within a year or two of planting |
| 'Miss Kim' (S. pubescens subsp. patula) | 5–7 ft | Mid- to late spring | Compact foundation shrub; blooms young |
| Japanese tree lilac (S. reticulata) | Small tree, 20–30 ft | Late spring to early summer, creamy white | A lilac you can use as a street or patio tree; good mildew resistance |
Sizes are from University of Minnesota Extension and the Morton Arboretum; mildew resistance and early bloom from Iowa State University Extension.
Lilac zones and climate
Missouri Botanical Garden and University of Minnesota Extension list common lilac for zones 3–7. Lilacs need a real winter: NC State Extension notes they require a long period of winter chill for the buds to mature, and Missouri Botanical Garden does not recommend them for hot, humid zone 8 and warmer, where unmet chilling leads to unreliable bloom. Bloom tends to be less reliable at the warm edge of zone 7.
If you garden at the warm end of the range, NC State Extension notes some low-chill cultivars have been developed, though even these bloom best after an extended, cold winter rest. Late frost can also kill flower buds, so a protected site helps.
Felco F-2 bypass pruners
Deadheading and stem thinning right after bloom go faster with a sharp bypass pruner; use a pruning saw for old stems at the base. See how we chose it.
When do lilacs bloom?
Common lilac blooms in mid- to late spring; Missouri Botanical Garden gives May for St. Louis. Exact timing follows the weather and your latitude, earlier in the warm end of the range and later as you move north or uphill. University of Minnesota Extension notes lilacs bloom for 10 to 14 days, depending on the weather.
To stretch the season, combine early-, mid- and late-season lilacs: University of Minnesota Extension groups them from early spring (hyacinth lilacs, April to mid-May) through mid- to late May (common lilac, 'Miss Kim', dwarf Korean lilac), and Japanese tree lilac blooms a little later than the shrub lilacs, into early summer (Morton Arboretum). Check what is flowering near you with what's blooming in your zone this week.
Lilacs bloom on old wood: University of Minnesota Extension notes they set next year's flower buds right after this year's bloom finishes. That one fact drives every pruning decision below.
Where and how to plant a lilac bush
- Sun: full sun, at least 6 hours of direct light. University of Minnesota Extension notes less sun reduces flowering and increases powdery mildew, and Oregon State University Extension recommends thinning overhead tree branches so the lilac gets plenty of sunlight.
- Soil: moist, well-drained soil with a near-neutral to slightly alkaline pH; University of Minnesota Extension gives pH 7.0 to slightly alkaline. NC State Extension notes lilacs do not do well in highly acidic or poorly drained soil. If a soil test shows strongly acidic soil, lime can raise it; see raising soil pH.
- Spacing: space plants for their mature size, 6–12 feet wide for common lilac. University of Minnesota Extension notes proper spacing increases air circulation and reduces powdery mildew.
- Planting: set the plant at the depth it grew in the pot, water after planting, and make sure the soil drains and does not pool. Mulch lightly, keeping mulch off the stems.
Young lilacs take time: University of Minnesota Extension notes blooming may begin in years 2 and 3, and Iowa State University Extension says common lilac cultivars often do not bloom for five or more years after planting.
Watering and fertilizing
Water regularly through the first growing season. Established lilacs handle dry spells reasonably well but benefit from water during long summer droughts, when next year's buds are forming. Water at the base rather than over the foliage.
Lilacs are light feeders. Iowa State University Extension says it is generally not necessary to fertilize lilacs, though they can be lightly fed in early spring, and University of Minnesota Extension suggests an all-purpose shrub fertilizer every few years once the plant is established (2 to 3 years after planting). Both warn that heavy nitrogen, including lawn fertilizer applied near lilacs, produces leaves at the expense of flowers.
When and how to prune lilacs
Prune immediately after flowering. Lilacs set next year's flower buds soon after bloom, so pruning in late summer, fall or winter removes them (Iowa State University Extension; Oregon State University Extension). This is the most common reason a healthy lilac in good sun fails to bloom.
Every year after bloom
- Deadhead spent flower clusters, cutting them off down to a pair of leaves, per University of Minnesota Extension. Oregon State University Extension notes removing faded flowers stimulates new growth and more blooms the following spring.
- Remove suckers you do not want at ground level. Missouri Botanical Garden advises promptly removing root suckers, particularly on grafted plants; on own-root lilacs you can leave a few well-placed ones as future replacement stems.
- Take out dead or damaged wood.
Renewal pruning for an older lilac
University of Minnesota Extension's renewal method is to remove a third of the thickest stems at the base each year until all the large stems are gone. Oregon State University Extension describes the same approach over two or three consecutive seasons, always right after flowering, and warns not to cut below the graft union on grafted lilacs. This keeps flowers at eye level instead of only at the top of tall, leggy stems.
Hard rejuvenation
For smaller, densely branched lilacs such as dwarf Korean (Meyer) lilac that have become overgrown, University of Minnesota Extension describes cutting the entire plant to the ground in late winter. New growth comes from the roots in spring, but expect little or no bloom for 1 or 2 years. The same approach is covered in coppicing shrubs for renewal.
Lilacs belong to the "prune after bloom" group of spring-flowering shrubs; see how to prune flowering shrubs and the pruning calendar.
Why a lilac won't bloom
| Cause | How to tell | Fix |
|---|---|---|
| Pruned at the wrong time | Shrub was cut back in late summer, fall or winter | Prune only right after bloom; expect flowers again the following spring |
| Too much shade | Fewer than 6 hours of sun; flowers only on the sunny side | Thin overhead trees or transplant to a sunny site |
| Too much nitrogen | Lush, dark leaves and long shoots, few buds | Stop fertilizing; keep lawn fertilizer away |
| Plant too young or just moved | Planted within the last few years; common lilac can take five or more | Patience; water during summer drought |
| Old, overgrown stems | Flowers only at the top of tall, woody stems | Start one-third renewal pruning |
| Climate too warm | Zone 8 or warmer, or mild winters at the edge of zone 7 | Grow low-chill cultivars or other shrubs |
The causes and fixes follow University of Minnesota, Iowa State and Oregon State University Extension, plus Missouri Botanical Garden for climate.
Cutting lilacs for a vase
Cutting flowers is a form of after-bloom pruning, so it does no harm to next year's display, and Missouri Botanical Garden rates common lilac a good cut flower. Cut stems in the cool of the morning using sharp pruners, strip the leaves that would sit below the water line, make a fresh cut on the woody stem end, and put stems straight into cool water.
Lilac problems
- Powdery mildew: a white coating on leaves in summer. Iowa State University Extension calls the damage mainly aesthetic and notes common lilac is highly susceptible while dwarf Korean and Preston lilacs are resistant; Missouri Botanical Garden says it generally does little permanent damage. Good spacing and full sun help. See powdery mildew on garden plants.
- Bacterial blight: Penn State Extension describes leaves that turn brown to black, girdled shoots and blackened flower buds; University of Minnesota Extension notes it is more common in cool, wet weather. Prune out infected branches well below the diseased tissue, disinfecting shears between cuts.
- Lilac (ash) borer: Iowa State and University of Minnesota Extension list this clearwing borer among lilac pests. Cut out wilting, damaged stems at the base, and keep up renewal pruning; see tree borer damage by gallery pattern.
- Scale insects: crusty bumps on stems; Iowa State University Extension lists oystershell scale. Prune out heavily infested stems; see scale insects on shrubs.
Common mistakes
| Mistake | Why it matters | Do this instead |
|---|---|---|
| Pruning in late summer, fall or winter | Removes the flower buds formed after this year's bloom | Prune immediately after bloom ends |
| Planting in part shade | Bloom declines steadily as shade increases | Site in at least 6 hours of direct sun |
| Shearing the shrub into a ball | Cuts off flower buds and thickens the outside, inviting mildew | Deadhead and thin whole stems at the base instead |
| Feeding with lawn fertilizer | High nitrogen gives leaves, not flowers | Skip fertilizer if leaves and bloom look good |
| Crowding lilacs against walls or other shrubs | Still, humid air encourages powdery mildew | Space for the full mature width with open air around it |
Frequently asked
When do lilacs bloom?
Common lilacs bloom in mid- to late spring, May in much of the Midwest per Missouri Botanical Garden, with the exact week set by local weather and latitude. University of Minnesota Extension notes each bloom lasts 10 to 14 days. Japanese tree lilac blooms a little later, carrying the season into early summer.
When should you prune lilac bushes?
Prune immediately after the flowers fade. Lilacs set next year's flower buds soon after bloom, so pruning in late summer, fall or winter removes them, per Missouri Botanical Garden, Iowa State and Oregon State University Extension.
How big do lilac bushes get?
Common lilac grows 8 to 15 feet tall and 6 to 12 feet wide, per University of Minnesota Extension, and Missouri Botanical Garden lists 12 to 16 feet, occasionally 20. Dwarf Korean lilac stays 4 to 6 feet, while Japanese tree lilac becomes a 20- to 30-foot tree. Plant for the mature size so you are not fighting the shrub later.
Do lilac bushes need full sun?
Yes. University of Minnesota and Iowa State University Extension both call for at least 6 hours of direct sun, and Missouri Botanical Garden notes best bloom is in full sun. A lilac in part shade may grow but will flower sparsely and get more powdery mildew.
Why is a lilac bush not blooming?
The usual causes are pruning at the wrong time, too much shade, too much nitrogen, or a plant that is still young; Iowa State University Extension notes common lilac may take five or more years to bloom after planting. Old, overgrown stems and a too-warm climate also cut bloom. Check sun and pruning timing first.
How long do lilac bushes live?
University of Minnesota Extension calls lilacs long-lived shrubs, and because they renew themselves from suckers a well-kept clump can last for many decades. Renewal pruning that replaces old stems with young ones keeps an old lilac productive.
How do you propagate a lilac bush?
Missouri Botanical Garden lists propagation by cuttings in spring. Lilacs also sucker from the roots, so on an own-root lilac a rooted sucker dug with its roots can be replanted. NC State Extension notes most lilacs are grafted, though, and suckers from a grafted plant come from the rootstock rather than the named variety.
Do deer eat lilacs?
Missouri Botanical Garden notes deer tend to avoid common lilac, and NC State Extension lists it as deer resistant. Hungry deer will still eat almost anything, especially young growth. Rutgers Cooperative Extension maintains a deer-resistance rating list for landscape plants, and fencing remains the only sure protection where deer pressure is heavy.
Sources
- Syringa vulgaris, Missouri Botanical Garden Plant Finder
- Syringa vulgaris (common lilac), NC State Extension Gardener Plant Toolbox
- Growing lilacs for Minnesota landscapes, University of Minnesota Extension
- Keep lilacs healthy and blooming with regular pruning, Oregon State University Extension
- How to manage potential problems growing lilacs, Iowa State University Extension
- Lilac diseases, Penn State Extension
- Japanese tree lilac, The Morton Arboretum
- Landscape plants rated by deer resistance, Rutgers Cooperative Extension