G1860

Lilacs

Lilacs are versatile, hardy, easy-to-grow and come in different shapes, sizes, and colors. Learn about the available cultivars and how to care for this popular shrub.

• Species
• Descriptions
• Propagation
• Culture
• Pests
• Cultivars
• Acknowledgments

Lilacs are among the most versatile shrubs grown in Nebraska. They come in various shapes, sizes, flower types, and flower colors. Time of flowering also varies with species and cultivars. Lilacs can be used statewide for wind screens, hedges, accent plants, or strictly for flower beauty and fragrance. Their drought and winter hardiness makes them easy to grow. They can survive, even when neglected, but perform better with care. Good soil drainage and full sun exposure are essential for optimal performance.

Species

About 26 species, and more than 4,000 cultivars (varieties), comprise the genus Syringa (lilac). The main species of lilacs grown in Nebraska include:

• Syringa meyeri, the Meyer lilac, is slow growing, with dense foliage and a broadly rounded plant shape. It grows from 4 to 8 feet high and equally as wide or wider. It has purple-violet flowers and begins flowering when quite young. A compact form is also available.
  
  
• Syringa microphylla is referred to as the Littleleaf lilac. Considered a compact form, it can grow to 6 feet in height and tends to be wider than tall. The cultivar ‘Superba’ is heat tolerant and mildew resistant and has dark pink, single flowers.
  
  
• Syringa oblata, the Early lilac, grows to a height of 10 to 12 feet and flowers in shades of purple.
  
  
• Syringa patula, the Manchurian lilac, has dense foliage, grows from 5 to 8 feet high and 4 to 5 feet wide. Its foliage often has an attractive fall color, and its primary flower color is lilac-purple. Its primary cultivar is called ‘Miss Kim’.
  
  
• Syringa reticulata, the Japanese Tree lilac, is often listed as a small tree rather than a large shrub. It grows 25 feet high and 20 feet wide. It bears white flowers in early to mid-June. Unlike most other lilacs, it is resistant to mildew, scales, and borers.
  
  
• Syringa villosa, the Late lilac, grows to a height of 7 to 10 feet and a width of 4 to 10 feet. The flowers are slightly fragrant and pinkish-white to lavender. Unlike many species, it does not sucker.
  
  
• Syringa vulgaris, the common or French hybrid lilac, is the most common and popular species. Its flowers are extremely fragrant, come in various flower types and in an array of colors from white to purple. Cultivars grow from 5 to 20 feet tall.

Descriptions

Lilacs are selected and described by both their flowering and foliage characteristics.

Flower Color

The general classes of flower colors of lilacs are white, violet, blue, lilac, pink, red, and purple. These petal colors may overlap in shades and tones and some are bicolor, such as found in the cultivar ‘Sensation’. Individual cultivars can vary in flower color shade because of weather, year, soil and location differences. Environment (hot versus cool and dry versus wet) and shade also can affect flower color.

Flower Type

Individual flower structure is listed as single or double. A single has four petals while the double has multiple sets of four petals.

Shape of Plant

Plants can vary in shape or form. They may be rounded, vase-like, tall and spreading, tall and straight, or intermediate between these shapes.

Time of Flowering

Flowering time is highly dependent on the species, cultivars, and spring weather conditions. Most lilacs flower from mid-May to the first of June. However, early, warm conditions will stimulate earlier flowering. Lilacs usually flower for two weeks. Flower buds are occasionally injured by a spring frost.

Fragrance

Fragrance varies, not only between cultivars and species, but also with temperature. On windy days, fragrance can be diluted. The common or French lilacs are the most fragrant.

Suckering

“Suckering” refers to a plant’s tendency to send up shoot sprouts from roots. Some cultivars sucker profusely and can spread into unwanted territory, others do not sucker and stay confined to a limited area. The only way to control suckers is to dig or cut them out.

Height

The height of lilacs varies between species and cultivars and certainly with age. The tree lilac, S. reticulata, can grow to a height of 25 feet while shorter cultivars, such as ‘Miss Kim’, may only grow to a height of 5 to 8 feet. More compact cultivars will be available in the future.

Foliage

Leaves vary in shape, size and color. Variegated leaf forms are also available.

Propagation

Lilacs are usually propagated by professional nurserymen. However, because many lilac varieties are not available through nurseries, the homeowner may have to propagate these themselves.

Root sprouts are usually the simplest and easiest way for the gardener to propagate many lilacs. Some cultivars send out suckers, near the base of the plant, which already have their own roots. These can be dug up and be permanently transplanted or set in a temporary nursery pot for later use. Rooted suckers are most successfully transplanted in early spring before buds start to unfold. They can develop into satisfactory plants within several years.

Layering is a slow but easy way to propagate plants. First, select a flexible branch and make a 2-inch slanting cut on the branch about 1 foot from the tip. Using a wire wicket or heavy object, fasten this branch to the ground between the wound and the base of the branch. Bend the tip of the branch upward at the wound and mound 2 to 4 inches of firmly packed soil over the wound. Water frequently. When roots have developed on the layered branch, cut it from the parent plant and leave this new plant in place. In several weeks, the rooted branch can be transplanted. This process takes about one year.

Cuttings can be used to propagate many lilac varieties. Cuttings, 8 to 10 inches long, taken in mid-June to early-July and treated with a rooting hormone, offer the best chance for success. Strip leaves from the cuttings’ lower 2 to 3 inches, dip in rooting hormone and place in a rooting medium of sand or perlite under high humidity. Once rooted, the plants can be potted in containers and later transplanted to the garden or landscape.

Grafting lilacs is challenging and requires planning. Privet (Ligustrum sp.) and ash (Fraxinus sp.), both in the same family (Oleaceae) as lilac, have commonly been used as an understock on which to graft lilacs. This method is useful to propagate non-suckering lilacs. Generally, though, lilacs do better on their own roots.

Seeds can also be used to propagate lilacs. This works well for species such as S. villosa and S. reticulata in which cultivars are not available. Seeds of some species require cold treatment, and others require a warm treatment for germination. Propagating lilacs from seed can be challenging and requires patience. This method is often left to those interested in developing new cultivars and those with experience in this area.

Culture

Lilacs are usually purchased as containerized or bare root plants. In Nebraska, they are normally planted in the spring but can be planted anytime during the growing season. Plants 2 to 4 feet tall are good selections to purchase.

Site Selection

Lilacs perform best in sites with soils high in organic matter and good water drainage, adequate nutrition and full sun.

Planting

Plants should be set 6 to 7 feet apart, but this varies with cultivar size and intended use. Plant the lilac at the same depth as it grew in the nursery.

Lilacs require moderate moisture during establishment but, once established, can endure dry weather better than most garden shrubs. Avoid planting where there will be competition with trees and other shrubs.

Maintenance

Lilacs are pruned or thinned out (not sheared) to maintain a desirable shape and size, to stimulate flowering, to remove insect injured and/or infested stems and to rejuvenate the plants. Lilacs should be pruned beginning three to four years after planting. A few of the older stems can be removed to the soil level each year to encourage younger, renewed stems. Pruning is generally done immediately after flowering. If selective pruning of older growth is too difficult, lilacs can be totally renovated by pruning the entire plant to 2 to 6 inches above the ground. In two to three years, the plant will resume flowering.

Removing the seed capsules soon after flowering has been reported to alter the every-other-year flowering cycle in some lilacs. This is because less energy goes into the current year’s seed production and more into the next year’s flower production. Some researchers agree with this recommendation and some do not. Removing seed capsules also improves the plant’s appearance.

Pests

Weeds can be a problem around lilacs but can be controlled by hand weeding or by mulching. For more extensive plantings, mechanical cultivators and/or herbicides can be used to control weeds.

Borers, insects that commonly burrow into lilac stems, cause leaves to wilt by inhibiting water movement. Severe borer injury can also cause the stems to break off. The larvae stage is a creamy-white caterpillar, about 3/4-inch long, that usually invades older branches first. Some lilac species are more resistant to borers than others. Appropriate pesticides applied at the proper time can reduce or eliminate borers.

Scales are small, shelled insects about 1/16-inch long. They injure plants by sucking sap from stems, weakening the plants. Scales can be controlled with horticulture oils.

Powdery Mildew is a disease affecting lilacs statewide. It is favored by shade and warm, humid conditions. A grayish white fungal growth develops on leaves, making them unsightly. New leaves may become distorted. Because the disease normally appears late in the growing season, it does little damage. Plant lilacs in full sun and in well drained areas with good air circulation. Air circulation can be improved by adequately spacing plants and pruning branches. Plant resistant cultivars or species.

Bacterial Blight starts as brown spots on leaves and stems as they develop in early spring. The spots turn black and enlarge rapidly, especially during wet weather. Leaves may become malformed, die and drop. Young stems are girdled, resulting in death of shoots and blossoms. Spots on mature stems enlarge along the stem, killing leaves only within the infected area. Space plants adequately and prune branches to provide good air circulation in the canopy. Prune infected branches 10 to 12 inches below visible infection and destroy them. Pruning should be done during dry weather. Keep plants healthy by properly fertilizing and watering. Avoid overhead irrigation. Plant resistant cultivars or species.

Cultivars

There are thousands of lilac cultivars to choose from. Some examples of commonly grown lilac cultivars that do well in Nebraska include:

In Nebraska, lilac collections can be seen at several locations. Important collections are located at The Maxwell Arboretum at the University of Nebraska–Lincoln, East Campus, south of the C. Y. Thompson Library, and at the Max and Darlene Peterson Lilac Collection located south of Ogallala.

Acknowledgments

The authors would like to recognize contributions made by Don Steinegger, retired Extension Horticulture Specialist and Todd Morrisey, Nebraska Statewide Arboretum, to the first edition of this publication.

This publication has been peer reviewed.