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. This week Iowa State University Extension garden experts have answers to questions about this deciduous shrub named after William Forsyth, an 18th century Scottish horticulturist. Gardeners with additional questions can contact the experts by emailing or calling the ISU Extension horticulture hotline at firstname.lastname@example.org or 515-294-3108.
Forsythias bloom on old wood. Unfortunately, the flower buds on some varieties are not reliably cold hardy in Iowa. For example, the flower buds on ‘Lynwood Gold’ and ‘Spring Glory’ are hardy to minus 10 degrees Fahrenheit. Since most areas in Iowa experience winter temperatures below minus 10 F, these cultivars often don’t bloom well in the state.
Improper pruning is another possible cause. Flower buds on forsythias begin to develop by early summer. Pruning the shrubs anytime from mid-summer until just prior to bloom will drastically reduce flowering. To achieve the best floral display, forsythias should be pruned immediately after flowering.
When selecting a forsythia, choose a cultivar that reliably blooms in Iowa. The flower buds on some varieties are not reliably cold hardy in Iowa. For example, ‘Lynwood Gold’ and ‘Spring Glory,’ typically don’t bloom well in Iowa as their flower buds are often killed by cold winter temperatures.
Forsythia varieties that grow well and bloom reliably in Iowa include ‘Meadowlark’ (bright yellow flowers, grows 8 to 10 feet tall, has arching spreading form), ‘Northern Sun’ (medium yellow flowers, grows 8 to 10 feet tall, has arching spreading form, University of Minnesota introduction), ‘Sunrise’ (medium yellow flowers, grows 5 to 6 feet tall, dense growth habit, an Iowa State University introduction), and ‘Northern Gold’ (yellow gold flowers, grows 8 to 10 feet tall).
Since they bloom on old wood, forsythias should be pruned immediately after flowering. Pruning the shrubs anytime from mid-summer until just prior to bloom will 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 shrubs will grow back quickly and should begin blooming again in one or two years.
Forsythias grow and bloom best in areas that receive at least six hours of direct 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.
The forsythia is an excellent plant for mixed shrub borders. It can also be utilized as an informal hedge. Low-growing cultivars can be used as groundcovers.
The forsythia is easily propagated from softwood cuttings. Softwood cuttings should be made from the current season’s growth in late June or early July. Using a sharp knife, cut off 4 to 6 inch long shoots. Pinch off the leaves on the lower half of the cutting. Dip the base (cut end) of the cuttings in a root-promoting compound. Root the cuttings in a large pot or flat containing coarse sand or perlite. Insert the bottom two inches of the cuttings into the rooting medium and firm the material around the base of each cutting. After all the cuttings are inserted, water the medium and let it drain. Cover the container and cuttings with a clear plastic bag or dome to reduce water loss. Then place the cuttings in bright light, but not direct sunlight. Forsythia cuttings should root in six to eight weeks. When the cuttings have well developed root systems, remove them from the rooting medium and transplant into individual pots using a well-drained potting mix.
PHOTO: Forsythia (440KB)