Common Name: Border Forsythia
Scientific Name: Forsythia x intermedia
Order: Lamiales
Family: Oleaceae
Description Border forsythia is a medium-sized ornamental shrub that matures at 8 to 10 feet tall and 10 to 12 feet wide. Each limb has medium green leaves that are 4” long, thin, oval shaped, arranged in an opposite fashion, and have toothed margins on the upper half of the leaf blade with a sharp tip. They are usually light green in color, but can be mixed with yellow, red, and maroon in the fall. The most appealing feature to border forsythia is the flower. The flower is 1 ¼ to 1 ½ inches long, bell-shaped, and range in color from pale to deep yellow. They are produced in clusters with 4 petals on each flower fused at their base. The flowers bloom before the foliage emerges and tend to bloom in late March to mid-April and effective only for a few weeks. Small brown capsules are formed on the limbs of the border forsythia, but are ornamentally insignificant.
Growth Habit Border forsythia has an erect habit, with most canes growing upright. It has an irregular form sue to a mix of upright & arching stems and the rapid growth rate. In young plants the growth habit is upright, oval, open, and straggly, and quickly matures to be arching, rounded, thick, and semi- pendulous.
Hardiness Zone(s) Border forsythia can grow in zones 4 through 8. This means that the plant can survive in temperatures as low as -30° F in the northern United States and 10° F in the southeast United States.
Culture For optimal flowering, border forsythia must have full sun to partial shade and placed in a moist, well-drained alkaline soil. Though this is where it would grow best, it is very adaptable to poor, rocky, dry soils as well as various pH levels, drought, pollution, and heavy pruning. The Forsythia hybrids compete successfully with the demanding roots of other shrubs and trees. Pruning should only involve thinning out older branches at the base of the plant. Any pruning after mid-July will cause the loss of many floral buds. Instead, prune the plant in the spring after flowering so that buds for the next year can develop in the fall. Border forsythia can be trimmed into a formal hedge, trimmed to reduce the size of the plant, or cut back to the ground & allowed to produce all new growth.
Diseases & Insects Botryosphaeria canker can be a problem on any woody shrub under extended drought conditions. Phomopsis gall is not common, but more frequently occurs on forsythia than other types of shrubs. They are spherical nodules that cluster along a branch and cause branch dieback.
Landscape Value Border forsythia plants are used for spring accents, row planting, group or mass plantings, formal or informal hedges, borders, entranceway cover, non-thorny barriers, or embankments. Sometimes it is improperly used at foundations where it becomes too large and pruning becomes frequent and the shrub loses most of its potential flower buds.
References Brun, C. 2015. Border Forsythia. Washington State University Clark County Extension, PNW Plants. Online.
This document was authored by Morgan Wheeler, Department of Agricultural Sciences, Louisiana Tech University, April 2015.