Everything you need to know about lilac

These easy-to-grow, low-maintenance, hardy shrubs grow best in northern states and areas with cool summers; however there are varieties available for warmer regions as well. The heavily-scented purple flowers on the common lilac (Syringa vulgaris) bloom in late May and attract hummingbirds, butterflies, and other pollinators. The cut flowers are perfect to bring the scent of spring right into your home. This upright, multi-stemmed, deciduous shrub can last decades in your garden.

LILAC BASICS

Zones:
Most lilacs are hardy in zones 3-8; however, there are varieties cold hardy to zone 2, like Scentara® Double Blue (S. hyacinthiflora). There are also varieties, like 'Lavender Lady' (S. vulgaris) that are heat tolerant to zone 9 and don't require a winter chill. Most others do require a cold, dormant period over winter.

Height/Spread:
The common lilac (Syringa vulgaris) grows 12 to 15 feet tall and 10 to 12 feet wide. There are many smaller dwarf varieties that mature at 4 to 6 feet tall and 3 to 7 feet wide. Japanese tree lilacs (Syringa reticulata) can reach 25 to 30 feet tall.

Exposure:
Lilacs need a minimum of 6 hours full sun for best flowering.

Bloom Time:
Most bloom in late May; however there are early spring, mid spring, and late-season blooming varieties, as well as new re-blooming varieties, like the Bloomerang® series.

Color:
The common lilac (Syringa vulgaris) has purple blossoms, dark gray-green to blue-green foliage (with no fall color change), and gray to gray-brown bark. However, there are officially 7 colors of lilac flowers: white, violet, blue, lavender, pink, magenta and purple with many shades within each color.

Other:
California lilac, mountain lilac and wild lilac aren’t true lilacs, but actually belong to the genus Ceanothus. Summer lilac is often used to refer to butterfly bushes, especially those types that are sterile and non-invasive.

PLANTING LILACS

When to plant:
Lilacs can be planted in early spring after the ground thaws or in fall before it freezes.

Where to plant:
For healthy and productive lilacs, plant them in an area with well-drained soil and where they'll receive at least 6 hours of sunlight daily. They'll also benefit from good air circulation to help prevent powdery mildew. Avoid planting in an area with grass directly underneath, as the regular watering can be too much for them. Also, grass fertilizers tend to be high in nitrogen, which is bad for lilacs.

How to plant:
When planting container-grown lilacs, dig a hole twice as wide and just as deep as the container. Gently remove the plant from the container and place it in the hole. Spread out the roots and back-fill with soil mixed with compost and water well. Clear a 2- to 3-foot area around the base and apply a loose layer of mulch to the area, keeping the mulch from touching the bark to prevent insect borers. Spacing should be 5 to 15 feet apart depending on the variety.

LILAC CARE

Pruning lilacs:

Since they bloom on old wood, lilacs should be pruned soon after flowering. Next spring’s flower buds are set almost immediately after flowering, so if you wait too long to prune, you’ll be sacrificing next year’s flowers. Prune not only for the health of the shrub by removing dead, diseased, or damaged branches, but also for shape and size. Pruning will also help in preventing powdery mildew on the leaves by improving air circulation throughout the plant. They are quite hardy and will withstand hard pruning, even down to as low as 6 to 8 inches; this may be needed to revive or rejuvenate an older specimen. However, keep in mind, it may take a few years to completely grow back, and blooms will be diminished in the first 2 to 3 years. Spent blooms should be deadheaded. Root suckers on grafted lilac plants should be removed when pruning.

Amendments & Fertilizer:

Lilacs won’t bloom well if over-fertilized. A small amount of 10-10-10 applied in late winter is sufficient. They do like rich soil, so add compost if needed. Jerry Fritz, of Linden Hill Gardens, says that ash from the fireplace can be sprinkled on soil around the base of the shrub.

Watering

Water regularly to establish a deep root system. It is best to water them at soil level and avoid overhead watering. Once established, lilacs are water wise. Water weekly in dry conditions, more often in extreme heat. Too little water can result in wilting or distorted leaves.

Propagation:

Seeds can be sown in spring. Seeds taken from specific cultivars may not come true from seed. In early summer, shoots from the base of the trunk can be used to propagate (not recommended for grafted varieties). Dig down at the base of the trunk and cut away the shoot, being sure to include some roots.

Diseases and Pests:

Powdery mildew on the leaves can be a frequent problem in summer and can greatly affect the foliage; however, it generally doesn’t do any permanent harm. Blights, leaf spots, and wilt can also affect lilacs, but cultivars such as the Bloomerang® series have been developed with exceptional disease resistance. Pests such as scales, borers, leaf miners, and thrips can be a nuisance as well.

LILAC DESIGN TIPS

Lilacs are an excellent choice for cottage-style gardens.
Plant where their fragrance can be enjoyed: near a pathway, main door, or window.
Use as single specimens, in small groups, mixed in borders, or as a deciduous hedge.
The blooms make excellent cut flowers and will last 3 to 5 days in fresh water. Cut single flowers when about one-third of the buds are open, cut double flowers when about half of the buds are open, cutting them at a slight angle.
Some suggested companion plants: boxwood, weigela, coneflower, juniper, maiden grass, Shasta daisy, phlox, and black-eyed Susan.

FREQUENTLY ASKED QUESTIONS

Why isn't my lilac blooming?
If your lilac is getting too much water or fertilizer, or not enough sunlight, it may experience diminished flower production. Also, if it was recently hard pruned, it may take a few seasons to get back to its full glory. Also, make sure that your annual pruning is being done correctly and you aren’t cutting off the “old wood” branches that produce the flowers.

Are lilacs poisonous?
They are not toxic to humans or animals.

Are lilac roots invasive?
Their roots do need space as they will spread to about 1-1/2 times the width of the shrub, but are not considered to be invasive.

LILAC FESTIVALS

Rochester Lilac Festival - Upstate New York
Lilac Time - Lombard, IL
Mackinac Island Lilac Festival - Mackinac Island, MI
Spokane Lilac Festival - Spokane, WA
Taos Lilac Festival - Taos, NM
The 4th Street Lilac Festival - Calgary, Alberta

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Credit: GARDEN DESIGN