Border Forsythia
 

Mature Size, Growth, Longevity

Average mature size 8-10' tall &10-12' wide, w/ upright-arching canes, needing a yearly pruning for a neat appearance. May sucker (slowly) to form colonies. Fast growth rate. Can become rampant.

Native Range

Both parents are from China.

Flower and Fruit Details

Perfect flowers, 1.25-1.5" long, 4-lobed, brilliant yellow, borne in clusters of 2-6, w/ good distribution along old wood, usually March-April for 2-3 weeks. Early spring bloom usually excellent, but can be injured by late freezes reducing flower quality. Fruits are two-celled, dehiscent, brown capsules, 0.33" long, often housing many winged seeds, but not ornamental.

Leaf and Bark Features

Deciduous: Leaves are ovate-oblong to oblong-lanceolate, simple, opposite, serrated along upper half of margin, 3-5" long and half as wide, glabrous, dark green above and lighter green beneath, w/ a 1/2" long petiole. Fall color is variable from year to year, Usually green or yellow-green, sometimes with a tinge of purple. Leaves hold late (November) and may turn a deep burgundy. Stems often somewhat squarish or 4-sided, yellowish brown and with many lenticels. Stems have a chambered pith in the internodes, solid at the nodes, but changing with age.

Culture and Care

Transplants easily. Prefers a good, loose soil but will do well in about any soil. Withstands city conditions and air pollution, and is pH adaptable. Plant in full sun to maximize flowering. Will tolerate some shade. Prune out old stems, or prune to ground after flowering. Winter temperatures of -10 to -15 degrees F will kill flower buds above the snow line. Tolerates deer, poor soils, clay soil, and juglone from nearby walnut trees. No serious diseases, but can get crown gall, leaf spots, dieback, four-lined plant bug, Japanese weevil, northern root-knot nematode and spider mites.

Strengths, Weaknesses, Other Facts

3-season interest: Spring, summer and fall. Flower buds may be killed at -15 to -20 degrees F, although such temperatures do not damage the stems or leaf buds. After a severe winter, flowering may only occur below the snow line, where the snow insulated the flower buds from the extreme cold. In Olive Family. A hybrid between weeping forsythia (F. suspensa) & greenstem forsythia (F. viridissima), the name "intermedia" refers to characteristics being intermediate between those of the parents.

Suggested Uses

Uses: shrub border, massing, groupings, or on slopes. Not ideal for foundation planting, but often used there.

Taxa and Plants of this Species at BCA