Forsythia Shrub grows well in hardiness zones 5 to 8, and many types are hardy to as low as -13 degrees Fahrenheit, but if a gardener really wants an explosion of flowers, it should be grown in the warmer part of its range. It grows from 6 to 9 feet high and 6 to 9 feet wide and as a hedge should be planted 4 to 6 feet apart. The flowers are tubular at the base and have star shaped lobes. The shrub usually grows about 24 inches a year. It like full sun to dappled shade and needs a medium amount of water. The forsythia doesn’t need much maintenance and does not have any major diseases problems.
The tough forsythia also tolerates being nibbled by deer, clay soil, compacted soil and pollution. It can even tolerate being planted near a black walnut tree, which usually poisons the soil around itself. But to keep a forsythia perfectly happy, it needs loose, somewhat moist and well-drained soil. It needs to be pruned to the ground immediately after its spring flowering. Old wood should also be removed. Pruning forsythia in the summer prevents it from flowering the next spring.
When the leaves finally appear on the forsythia, they are 3 to 5 inches long and 1 inch wide, bright green, opposite and toothed around their upper half. In the fall they turn yellow, though in some cultivars the leaves are purplish. As the shrub leafs out the spent blossoms fall to the ground, and in some species they will take root there since the forsythia actually self-fertilizes.