Colorado State University Extension Master Gardener in Larimer County
June 18, 2011
Lilacs were brought to America by the earliest settlers, dating back to the mid 1750s. Lilacs were grown in America’s first botanical gardens and were popular in New England. Both George Washington and Thomas Jefferson grew lilacs in their gardens. Later they were carried west by the pioneers. Lilacs are natives of colder regions of southeastern Europe and northern regions of China and Korea.
What we call Common Lilac, (Syringa vulgaris) came from Romania, Yugoslavia and Bulgaria. This species of lilac 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 six 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 single flowers (purple with white edges); and ‘Victor Lemoine’ – lilac double flowers (very fragrant)
For later blooming lilacs try one of the Preston cultivars. These lilacs have elongated leaves that are more resistant to powdery mildew. Two Preston cultivars include: ‘Donald Wyman’, which has purple single flowers and ‘Miss Canada’ that blooms pink single flowers.
Meyer Lilac (Syringa meyeri) grows four to eight feet tall with a width of six to 12 feet. These cultivars form a dense, broad-mounded shrub. Flowers are violet-purple in color and occur on panicles four inches long and over two inches wide. The flowers emerge before plants are fully leafed out. This species is not affected by powdery mildew.
Syringa patula, the Manchurian lilac, has an upright form and grows nine feet tall. The flower panicles often originate in pairs from the terminal buds from last year’s growth. These panicles range in length from four to six inches with lilac-purple flowers. The most commonly found cultivar is ‘Miss Kim’, which usually grows five to six feet tall and four to five feet wide. This lilac is a mid season bloomer.
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. This lilac has large panicles of fragrant white flowers. Good cultivars include: Ivory Silk, Chantilly Lace, Regent and Summer Snow. A related species, Syringa pekinensis (Pekin lilac) is a smaller tree growing 15 to 20 feet tall. This lilac is often multi-stemmed and finer in texture than the Japanese tree lilac. Flowers are creamy white on three to six-inch long panicles. These lilacs are very late bloomers.
Lilacs are adapted to USDA Zones 3 to 5 and milder areas of Zone 2. Lilacs thrive in sunny sites with good air circulation. These plants need at least four to six hours of sunlight a day for best flower production. The ideal soil for growing lilacs is a loam that is not too rich and that is neutral or alkaline. Space plants 10 to 15 feet apart for specimen displays and five to eight feet apart for a hedge.
After lilacs have bloomed, remove the spent flower heads. Removing these will help the plant to produce more flowers for the next season’s display. If you want to shape the plant, wait until after bloom, then prune. Rejuvination pruning also works well on established plants that are losing their shape. Remove one-third of the oldest, thickest canes at the base in late winter or early spring—knowing you are removing flower blooms. While flower numbers will be reduced, this pruning will eliminate much of the self-shading from overgrown foliage resulting in a better looking shrub than tip pruning alone. This pruning will remove the canes that are most likely to be badly infested with scale and borers.
Because lilacs are grown chiefly for their attractive, fragrant flowers, many gardeners are disappointed when plants don’t bloom quickly. Lilacs must grow and mature before they are capable of blooming. Exposure could also be a factor. 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. 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. Planting varieties resistant to powdery mildew is the easiest, least expensive and preferred method of disease management.
The author has received training through Colorado State University Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.
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Updated Tuesday, July 22, 2014