The yellow bell bush, or forsythia (Forsythia x intermedia) is a rangy shrub growing to 10 feet tall and 8 feet wide. There are several varieties available in the nursery trade with the most common being the border forsythia (Forsythia x intermedia 'Spectabilis'). The outstanding feature of the forsythia is the multitude of yellow flowers that appear along the bare stems in early spring before the leaves emerge.
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After the spring bloom period, the forsythia tends to fade into the landscape. Also, it can become shaggy looking, especially in warmer climates. Plant forsythia behind shorter blooming perennials or behind annual flowers so the rangy stems are not as visible once the flowers fade. Another way to plant forsythia is in a large groups of three or more plants planted as close as 3 feet apart. That way, the many branches will overlap and create a mass of green. Forsythia can also be used as a single specimen plant.
Forsythia is suitable for planting in U.S. Department of Agriculture plant hardiness zones 4 and warmer. It grows best in full sun to part shade, which means exposure to at least four hours of direct sunlight each day. The more sun exposure a forsythia has, the better the bloom production. The soil should be well-drained and not waterlogged. Plant at least 10 feet from a structure or walkway to avoid the need for constant pruning to keep the fast-growing plant in bounds.
Forsythia requires evenly moist, but not waterlogged, soil throughout the growing season. An annual application of 1 inch of fresh compost covered with a 2-inch layer of compost is sufficient to conserve moisture, control weeds and supply a low level amount of nutrients throughout the growing season. If desired, you can fertilize with a fertilizer that is specifically labeled for blooming shrubs. Follow the directions carefully as over-fertilization will cause the leaf margins to turn brown and encourage tender new growth susceptible to disease and insect damage.
Prune forsythia in late spring after the blooms have faded. Forsythia require a specific pruning technique to maintain a natural shape and encourage maximum bloom production. Do not shear forsythia plants as you would a hedge or try to shape the plant into a ball. To properly prune a forsythia, locate the longest or most unruly stem first and cut that stem at the ground level. Next, find another unruly stem and cut that one back the same way. Continue cutting the longest stems until the shrub is the desired size. Vigorous new growth will grow from the base of the plant and fill in where the limbs were removed. Limbs that arch over and touch the ground will root to form new shrubs. Prune back arching branches in the same manner, unless you want to propagate new forsythia.
Forsythia bloom best on wood that is two years old or older, so only prune as needed, and always prune out any dead wood. The best way to avoid pruning a forsythia often is by planting it where it has plenty of room to grow.