lilac bloom

Common lilac (Syringa vulgaris)
Photo: Miri Talabac, HGIC

Updated: August 16, 2022

Key points

  • Common lilac (Syringa vulgaris) is a woody shrub grown for its extremely fragrant flowers in mid to late spring, depending on the location.
  • There are several species of lilacs but Syringa vulgaris is the most commonly planted species in Maryland.
  • Named cultivars can have a wide range of flower colors including lilac, purple, white, pink, and a reddish hue.
  •  Lilacs can become bare-bottomed or leggy with age and often look bedraggled after a hot summer with leaf infections. Planting shorter shrubs or perennials in front of them can distract from this eyesore and provide more seasonal interest.
  • Lilacs are prone to powdery mildew and other diseases. It is important to give them adequate spacing when planting. This improves air circulation around the foliage and reduces the spread of disease by keeping moisture levels low.

Growing lilacs in Maryland

Site

Requires full sun and neutral to slightly acidic, well-drained soil. Deer usually avoid browsing on lilac foliage. Not very heat-tolerant, so avoid locations near sources of reflected heat or limited airflow, such as next to walls, pavement, or solid fencing.

Spacing and mature size

8’ - 12’ tall by 6’-8’ wide. Space them at least 6’ apart. Plant them where they can be enjoyed during the brief flowering period in May but can fade to the background in the summer. Dwarf varieties are available for smaller spaces. Be sure to give all types of lilac plenty of space so that the foliage is not crowded. Good air circulation reduces the spread of disease.

Disease and insect resistant lilacs

blooming Bloomerang lilac
‘Blomerang’ growth habit
Photo: Miri Talabac, HGIC
  • Bloomerang ® series of lilacs is powdery mildew resistant and reblooms. Like many dwarf hybrid lilacs, the Bloomerang series is more disease-resistant than typical Syringa vulgaris and matures shorter in height. Members of this series also have the distinction of sporadically re-blooming later in the summer or autumn.
  • Syringa vulgaris cultivars with above-average powdery mildew resistance include ‘Charles Joly,’ ‘Sensation,’ and ‘Old Glory’.
  • Japanese tree lilac, Syringa reticulata, a lovely small tree or large shrub, has moderate resistance to powdery mildew, scale, and borers. It is susceptible to bacterial blights, Phytopthora, and leaf spot. It grows  to 30' tall and 20' wide 
'Miss Kim' lilac fall color
‘Miss Kim’ fall color
Photo: Miri Talabac, HGIC
  • Syringa patula ‘Miss Kim’ – matures about 4-7’ in height; blooms slightly later than common lilac; powdery mildew resistant; deep burgundy fall color.
  • Syringa meyeri ‘Palibin’ – matures about 4-5’ tall and 5-7’ wide; blooms slightly later than common lilac; powdery mildew resistant.
  • Syringa ‘Tinkerbelle’ is a cross between Syringa meyeri ‘Palibin’ and Syringa microphylla ‘Superba’ with good powdery mildew resistance.
  • Littleleaf lilac, Syringa microphylla, is heat tolerant and mildew resistant. 

Pruning

  • Lilacs can become leggy and unproductive if not pruned regularly after flowers fade. Younger growth blooms better than older growth.
  • Lilacs will lose their lower branches with age. 
  • If you cut the entire plant to the ground, you will not have blooms for a couple of years. Instead, prune out ⅓ of the oldest stems each year down to the ground level. A folding pruning saw is the best tool for working in tight spaces between stems.
  • Prune after flowering in early summer. Remove damaged stalks first. Then choose the oldest growth to cut to the ground. To minimize crowding, choose to keep young stems that are growing on the outside edges instead of the center of the plant. Make sure stems are not crossing each other where bark will rub off.
  • See the “thinning” and “renewal pruning” sections of the Pruning Shrubs and Hedges page for more guidance on how to maintain lilacs.

Abiotic problems and disorders of lilac

Poor flowering

  • Improperly timed pruningonly prune immediately after flowers fade, or else you run the risk of removing flower buds that have already formed for the following year.
  • Too much nitrogen fertilizer - promotes green leafy growth at the expense of flower production.
  • Not enough sunlight – the ideal amount is at least 6-8 hours of direct sun per day in summer.
  • Recovery from a severe pruning – plants may need a few years before regrowth is mature enough to flower again.
  • Trending warmer wintersCommon lilac (Syringa vulgaris) flower buds need a period of winter chill to develop and bloom fully in the spring.  

Lilacs aren’t very heat-tolerant

  • Excessive summer heat results in shriveled leaves, premature leaf drop, and lack of vigor.
  • Plants under stress may also be more vulnerable to insect pests and infection.
  • Climate change makes growing lilacs successfully a challenge, especially in the warmer areas of Maryland.
  • Consider replacing older unproductive lilacs with alternatives (several are listed below).

Lilacs do not age gracefully on their own

  • The branches become sparse, leggy, and unproductive over time.
  • Lilacs need regular renewal pruning to keep them vigorous and free-flowering.

Diseases of lilac

Bacterial blight

flowering lilac with bacterial blight on stem
Bacterial blight of lilac
Photo: UME/HGIC

 Symptoms and cause

  • Bacterial blight of lilac is caused by the bacterium Pseudomonas syringae cv. syringae.
  • This bacterium is commonly found on leaf surfaces as part of the natural population of microorganisms on plants.
  • Early symptoms include the blackening of new green shoots, leaves, and flower buds. Leaf symptoms are irregular dark spots on leaves sometimes ringed by yellow halos. Leaf spots quickly grow together and blight entire shoots.
  • Rainy, mild spring weather promotes the disease.
  • In Maryland, spring frost damage and late fall or winter pruning seem to predispose shoots to bacterial blight infection.
  • Older woody stems are rarely attacked.
lilac leaves infected with leaf blight
Symptoms of bacterial blight (Pseudomonas syringae) on a lilac
Photo: William Jacobi, Colorado State University, Bugwood.org

Prevention and management

Avoid overfertilization and excessive pruning to prevent an overabundance of young susceptible shoots in the spring.

Prune or thin out lilacs in early summer, after flowering, to promote better air circulation and allow time for wounds to heal before the next season.

Prune out diseased shoots right away during dry periods and remove the clippings from the area to prevent reinfection.

Fungal leaf spots

fungal leaf spot on lilac leaf
Pseudocercospora leaf spot on lilac
Photo: D. Clement, UME,HGIC
  •  Most leaf spots aren’t life-threatening to lilacs; they are more of a cosmetic issue. No treatment is recommended.
  • The best management practice is to prune off infected leaves and dead twigs during the winter or dry summer months to prevent the spread of the disease spores.
  • Keep lilacs well-spaced and properly pruned to encourage good air circulation around the foliage. Leaves that dry quickly after rain or dew are less vulnerable to infection.
  • Collect and dispose of infected fallen leaves in autumn.
  • Learn more about fungal leaf spots.

Powdery mildew

Powdery mildew commonly infects lilac
Powdery mildew commonly infects lilac
  •  Powdery mildew is a common fungal disease of lilacs.
  • The white powdery fungal spores grow on the surfaces of leaves, young stems, and shoot tips, blocking light needed for photosynthesis.
  • Despite this, powdery mildew is more unsightly than a serious health risk.
  • Warm days followed by cool, humid nights provide ideal conditions for the fungus.
  • Learn more about Powdery Mildew.

Prevention and management 

Select resistant cultivars.

Plant in full sun since leaves do not dry as quickly in shade.

Maintain good air circulation by avoiding crowding, which reduces humidity levels that can promote mildew outbreaks. Space plants 6’ - 10’ apart.

Keep lilacs pruned regularly.

Monitor for watering needs during dry weather.

Insect pest of lilac

Lilac-ash borer 

adult lilac ash borer
Lilac-ash borer adult
Photo: Suzanne Klick, UME
  • Lilac borer, Podosesia syringae, is a clearwing moth that resembles a wasp in appearance.
  • They are a serious pest of lilac and ash trees (ash trees are scarce in the landscape due to emerald ash borer). 
  • The moths emerge in mid-May and lay eggs on the bark.
  • The hatched larvae tunnel into the wood and feed, boring into the heartwood.
  • As they feed they push frass out of the tunnels via the holes.
  • Continual reinfestation of the shrub will result in branch dieback. Heavy infestations may kill plants.
wilted stems caused by lilac borer
Severe wilt due to lilac borers
Photo: UME/HGIC

 

small lilac borer exit hole in lilac stem
Photo: Lilac borer exit hole on a branch

Management

To prevent borers, keep mulch away from the base of the shrub. Keep shrubs well-watered during dry periods. Avoid wounding the stems, especially with lawnmowers and string trimmers.

Look for dead stems in the center of a lilac bush. Examine them for holes in the bark. Pupal cases may be visible at adult exit holes. Prune out all of the dead and dying stems as close to the ground as possible.

The best management option is to prune out and destroy wilting branches.

There are no conventional insecticides that will kill borer larvae once they are inside the branches.

Alternatives to lilac 

No plant can provide all of the traits that make lilacs popular – fragrance, spring bloom, and their namesake color. If you desire to plant an alternative, prioritize which traits are most important to you.  Be sure to research the plants before purchasing. Their mature size and shape often differ from lilacs, and some of their cultural needs (sun exposure, soil moisture, etc.) are different and might be better suited to another part of the yard. For showy spring flowers, there are several native plants to consider. 

Trees

Flowering dogwood, Cornus florida

pink dogwood blooms
Cornus florida with pink flowers
Photo: D. Ricigliano, HGIC
  • Prefers light shade and blooms in mid-spring. Flowers are white or range from pale to deep pink.
  • Be sure to look for cultivars resistant to powdery mildew and discula anthracnose. See the table of disease-resistant dogwoods on our Dogwood: Identify and Manage Problems page.

Eastern redbud, Cercis canadensis

red bud tree in bloom with magenta pink flowers
Eastern redbud
Photo: Ria Malloy, UME/HGIC
  • Reddish-purple buds open to magenta or rosy pink flowers directly attached to the branches. There are also pure white forms. The display is spectacular for 2-3 weeks in April.
  • A member of the legume (pea) family, the flower shape is the same as garden peas and the flowers are edible.

Fringetree, Chionanthus virginicus

white blooms on a fringe tree
Fringetree in bloom
Photo: Ria Malloy, UME/HGIC
  • Flowers are white and slightly fragrant, with large clusters of thin petals. Blooms in late April or early May. Plants can be single-stemmed trees or resemble a multi-stemmed shrub while young.
  • If pollinated, female trees will produce dark blue olive-sized berries attractive to birds.

Shrubs

If fragrance is what you desire there are some native and non-native options to consider, although none can truly compare with lilac. 

Carolina Allspice (Calycanthus floridus)

  • Native to the southeast but sufficiently hardy, spring blooms resemble miniature waterlilies and come in maroon or pale lime-green. Scents can vary a bit from plant to plant but tend to be fruity and/or spicy.
  • Deer resistant.

Deciduous azaleas

  • Several deciduous azaleas, including Swamp Azalea (Rhododendron viscosum), Sweet Azalea (R. arborescens), Alabama Azalea (R. alabamense), Coast Azalea (R. atlanticum), Roseshell Azalea (R. prinophyllum), and Pinxterbloom Azalea (R. periclymenoides).
    • All are either locally native to native to the eastern U.S.
    • Bloom season varies with species but ranges between mid-spring and early summer overall.
    • Several species display showy autumn leaf colors.
    • Visited by hummingbirds and large butterflies.

Summersweet (Clethra alnifolia)

  • Locally native and beloved by pollinators.
  • Flowers are intensely sweet-scented and appear in summer. White is the most common color, but there are a couple of pink cultivars.
  • Deer resistant.

Native roses

  • Native roses, such as Swamp Rose (Rosa palustris), Carolina Rose (R. carolina), and Virginia Rose (R. virginiana).
    • Blooms are simple, with only five petals and a pink color, but the scent carries well and the flowering period is half the summer or more.
    • Autumn hips (fruits) have good wildlife value and blooms are attractive to pollinators.

False Holly (Osmanthus heterophyllus)

  • Unrelated to true hollies but has very similar prickly evergreen foliage.
  • Some cultivars have colorful foliage.
  • Blooms are white and small, but the scent carries well. Very late-flowering, between mid-October and mid-November.
  • Non-native. Deer resistant. 

Mockorange (Philadelphus)

  • Blooms are white and appear in May or early June, with some cultivars able to re-bloom sporadically into summer.
  • Non-native.

Author: Ria Malloy, HGIC. 2021

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