Forsythia x intermedia (Border Forsythia) is a deciduous shrub forming a graceful fountain with its upright-arching to spreading branches bending to the ground. They are clad with ovate, sharply serrated, medium to dark green leaves, up to 5 in. long (12 cm), which die off green or with a hint of burgundy in the fall. In early to mid spring, a profusion of brilliant yellow, four-petaled flowers open on the naked branches. The flower effect is spectacular, brightening the landscape at a time when not much else is in bloom. Border Forsythia is extremely adaptable, tolerating most soils and climates.
This tough deciduous shrub thrives in a wide range of conditions. Forsythias are tolerant of a wide range of soil conditions, but prefer well-draining soil amended with rich organic matter. It is also somewhat drought tolerant once established.
It is suitable for light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. It is also suitable for mildly acid, neutral and basic (mildly alkaline) soils and can grow in very alkaline soils. It can grow in full shade (deep woodland) semi-shade (light woodland) or no shade. It prefers moist soil.
History and Introduction
A plant of seedling origin was discovered growing in the Göttingen Botanical Garden in Germany. It was introduced to the Arnold Arboretum of Harvard University in Boston in 1889.
Forsythia is considered invasive as it is stoloniferous and extremely difficult to remove. Some varieties are sterile, so seeding is not usually the problem; it’s the root systems. It doesn’t colonize and crowd out native plants like Japanese Barberry or Winged Euonymus do. These plants escape from their original site and can spread quickly and easily.
Forsythia is stoloniferous. This means that when the tip of a Forsythia branch touches the ground, it can root and start another bush.
One of the most difficult plants to eradicate is Forsythia. Forsythia plants grow from deep taproots, and you must dig deep into the soil to completely kill forsythia roots. If you don’t uproot the central taproot entirely from the soil, the plant will grow again and affect any other crops you plant on the soil. You can cut off other roots, but the Forsythia taproot must be uprooted entirely to prevent it from growing back.
A repeated herbicide application is needed to eradicate it from the ground completely. An effective strategy to get rid of the root system is to spray an herbicide on Forsythia, and wait for some weeks for the branches and foliage to wilt. After, cut the branches using pruning shears then dig a trench about 12-15 inches deep around the shrub. Finally, dislodge the roots by turning them over with a shovel.
There is a chance that suckers may emerge from the ground after cutting the roots. You can get rid of them by making use of an herbicide that contains triclopyr.