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James Romer, Horticulture Extension, (515) 294-2336,
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Yard and Garden Column for the Week Beginning May 25

Lilacs in Iowa Landscapes

By James Romer
Extension horticulturist
Iowa State University Extension

A springtime favorite of many Iowans is the lilac. Though they offer mainly one season of interest, their spring flower displays are greatly appreciated after a long, hard winter. There are several different types of lilac available to include in the home landscape.

The most widely planted of all types are the common lilacs, Syringa vulgaris, also known as French hybrid lilacs. These shrubs are easily identified by their large bloom sizes and wonderful fragrances. This genera of lilacs became known as French hybrids due to Victor Lemoine, a French hybridizer, who was responsible for approximately 200 different cultivars dating back to the 1870s. The common lilac will attain a height of 10 to 15 feet and spread of 6 to 12 feet. There are seven color classifications for the common lilac: blue, lilac, magenta, pink, purple, violet and white. Flowers are single or double in form. Some outstanding cultivars of Syringa vulgaris include:

'Agincourt Beauty' -- Violet single flowers (late midseason bloomer)
'Charles Joly' -- Magenta double flowers (fairly resistant to mildew)
'Edmond Boissier' -- Purple single flowers (one of the darkest)
'Leon Gambetta' -- Pink double flowers (profuse bloomer)
'President Lincoln' -- Blue single flowers (truest of the blues)
'Sensation' -- Bicolor of single flowers (purple with white edges)
'Victor Lemoine' -- Lilac double flowers (very fragrant)

For later blooming lilacs, try one of the Preston cultivars. Preston lilacs have elongated leaves that are more resistant to powdery mildew. Two cultivars include:

'Donald Wyman' -- Purple Single flowers
'Miss Canada' -- Pink Single flowers

Meyer Lilac, Syringa meyeri, grows 4 to 8 feet tall, with a width of 6 to 12 feet. These cultivars form a dense, broad-mounded shrub. Flowers are violet-purple in color and occur on panicles 4 inches long and 2 1/2 inches wide. They emerge before plants are fully leafed out, usually early to mid-May. This species is not affected by powdery mildew, as are many of the other species.

Syringa patula, the Manchurian lilac, has an upright form and grows 9 feet tall. The flower panicles often originate in pairs from the terminal buds from the last year's growth. They range in length from 4 to 6 inches with lilac-purple flowers and appear in late May to June. The cultivar most commonly found in the trade is 'Miss Kim,' which usually grows 5 to 6 feet tall and 4 to 5 feet wide.

The Japanese tree lilac, Syringa reticulata, grows 20 to 30 feet tall with a spread of 15 to 25 feet forming an oval- to round-shaped small tree. The large panicles of fragrant white flowers appear in early to mid-June. 'Ivory Silk,' 'Chantilly Lace,' 'Regent' and 'Summer Snow' are good cultivars. A related species, Syringa pekinensis, the Pekin lilac, is a smaller tree, growing 15 to 20 feet tall. It is often multi-stemmed and finer in texture than the Japanese tree lilac. The flowers are creamy white on 3 to 6 inch long panicles in late May to June.

Lilacs are adapted to USDA Hardiness Map zones 3, 4, 5 and milder areas of zone 2. They thrive in sunny sites with good air circulation. Lilacs on their own roots are much more hardy than grafted lilacs. Lilacs need at least 4 to 6 hours of sunlight a day for best flower production. Space plants 10 to 15 feet apart for specimen displays and 5 to 8 feet apart for a hedge effect.

Since many lilacs have bloomed, now is the best time to remove the spent flower heads. This will help the plant to produce more flowers for next season's display. While pruning a lilac in late winter or early spring is done to remove the oldest stems, flower numbers will be reduced. In the long run, one will come out ahead by continually removing one-third of the oldest branches in the late winter or early spring.

Since lilacs are chiefly grown for their attractive, fragrant flowers, many gardeners are disappointed when plants don't bloom quickly. Lack of flowering may be due to several factors. While Syringa meyeri 'Palibin' will flower when quite small, many lilacs won't bloom for 4, 5 or more years after planting. Lilacs and most woody plants must grow and mature before they are capable of blooming. Exposure also could be a factor. Lilacs need at least 6 hours of sun to bloom well. Improper pruning is another possibility. Many lilacs bloom on the previous season's growth. The flower buds form during the summer months. Pruning lilacs in fall or late winter could remove much of the blooming wood. There is little that an individual can do to encourage lilacs to bloom. Fertilizing the shrubs encourages vegetative growth, but may actually delay flower formation.

Powdery Mildew is a disease that affects lilacs, infesting the leaves and leaving a gray film on the leaf surface. Because the disease normally appears at the end of the growing season, it seldom does permanent damage to the plants. Lilacs should be planted in full sun and in areas with good air movement to discourage this disease. Humid, overcast weather when days are warm and nights are cool favor powdery mildew development. Planting varieties resistant to powdery mildew is the easiest, least expensive and preferred method of disease management. Unfortunately, variety descriptions are often ambiguous and don't identify resistance to specific diseases. Varieties of various lilacs differ in their mildew susceptibility, so ask about disease resistance to powdery mildew when buying them.


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