By Richard Jauron
Iowa State University Extension
After a long, drab winter, most gardeners anxiously await the arrival of spring. One sure sign that spring has truly arrived is the bright yellow flowers of the forsythia. Named after William Forsyth, an 18th century Scottish horticulturist, the forsythia is a deciduous shrub that is native to China, Korea and Europe.
In Iowa, forsythias typically bloom in early to mid-April. The four-petaled flowers vary from light yellow to bright golden yellow and persist for 10 to 14 days. Flowers are produced in groups or clusters along the stems. Forsythias bloom only on old wood.
Leaves emerge shortly after flowering. Forsythia leaves are medium to dark green in summer. Fall leaf color is usually poor. Occasionally, however, leaves may turn pale yellow to reddish purple in fall. Forsythias are one of the last deciduous shrubs to drop their leaves in fall. In Iowa, leaf drop typically occurs in late October or early November.
Forsythias are fast growing shrubs. Many cultivars (varieties) have spreading, arching growth habits and can reach a height of 8 to 10 feet.
Forsythias grow and bloom best in full sun. They will grow in partial shade, but won't bloom as heavily. Forsythias adapt to a wide range of soils. However, they do not perform well in wet, poorly drained sites. Forsythias do not have serious insect or disease pests.
The forsythia is an excellent plant for mixed shrub borders. It can also be massed on sunny slopes or used as an informal hedge. Low-growing cultivars can be used as groundcovers.
When selecting a forsythia, choose a cultivar that reliably blooms in Iowa. The flower buds on some cultivars in Iowa are not reliably cold hardy. For example, the flower buds on 'Lynwood Gold' and 'Spring Glory' are hardy to -10 degrees F. Since most parts of Iowa experience winter temperatures below -10 degrees F, these cultivars often don't bloom well in the state.
An excellent forsythia for Iowa is 'Meadowlark.' Jointly introduced by North Dakota State and South Dakota State Universities, in collaboration with the Arnold Arboretum, 'Meadowlark' will bloom after exposure to temperatures down to -30 degrees F. Flowers are bright yellow. 'Meadowlark' is a vigorous, rapidly growing shrub. Its height and width are 8 to 10 feet. 'Meadowlark' has a spreading, arching form.
'Northern Sun' is another good choice for the upper Midwest. Introduced by the University of Minnesota, 'Northern Sun' will flower after temperatures drop to -30 degrees F. The spreading, arching shrub grows 8 to 10 feet tall and has a similar spread. Flowers are yellow-gold.
Introduced by Iowa State University, 'Sunrise' is an excellent cultivar for southern and central Iowa. Its flower buds are hardy to -20 degrees F. Plants are covered with masses of small, medium yellow flowers in early spring. 'Sunrise' is a semi-spreading, compact shrub with a mature height and width of 5 feet. Its compact size makes 'Sunrise' ideal for small hedges or shrub borders.
Other forsythia cultivars that bloom well in Iowa include 'Northern Gold,' 'New Hampshire Gold' and 'Vermont Sun.'
While most forsythia cultivars are grown for their attractive yellow flowers, a few are grown for other features. 'Bronxensis' is a low-growing cultivar that is often used as a groundcover. Plants commonly grow 18 to 24 inches tall. Unless covered by snow, 'Bronxensis' doesn't usually bloom well in Iowa as its flower buds are hardy to -10 degrees F. Gold Tide(R) is another low-growing forsythia. The compact, spreading plant grows 2 to 3 feet tall. Its flower buds are hardy to -15 degrees F. Gold Tide(R) is commonly used as a groundcover and foundation planting. 'Fiesta' is a compact shrub with variegated foliage. Plants typically grow 3 to 4 feet tall. Leaves are green with yellow centers.
Forsythias are easy to grow, but do require some maintenance. Pruning is the most important chore. Proper pruning produces healthy, vigorous, heavily blooming shrub. Since they bloom on old wood, forsythias should be pruned immediately after flowering. Pruning the shrubs from mid-summer to late winter will drastically reduce flowering in spring.
When pruning mature forsythias, it's best to remove one-fourth to one-third of the oldest (largest) stems at ground level every other year. New shoots will emerge from the ground and bloom in following years. Old, neglected forsythias can be rejuvenated by pruning them back to within 3 to 4 inches of the ground in late winter or early spring. The rejuvenated shrubs will grow back quickly and should begin blooming again in one or two years.
Some shrubs provide multi-season interest with attractive flowers, fruits or foliage. While the forsythia is rather one-dimensional, its yellow flowers are a beautiful, welcome sight in the spring landscape.