How Tall Can Johnson Grass Grow?

Description

• Johnson grass is a clumping-type perennial grass that reproduces rapidly in colonies. Reproduction is through seed drop and rhizome roots or stems. Root and stem fragments sprout easily into new plants. The tall, erect stems reach 6 to 8 feet in height at maturity. The stems do not branch and its coarse leaves roll in at the bud juncture to the stem. The leaves are flat and sparsely hairy with a white mid-vein. Flower heads develop May to October for autumn seed dispersal. Flowers are pyramid-shaped with large, open branches. They appear green or green-violet as they begin to grow, changing to dark red or purple at maturity. The root system of Johnson grass is thick, fleshy and segmented.

Seedlings

• The seedlings are similar to corn seedlings, but its first leaf grows parallel to the ground. It emerges in spring and forms seed by July. Its dark, reddish-brown to black seed stays attached after removing the seedling from the ground. Leaf blades are hairless with smooth edges. Leaves grow 6 to 20 inches long. Stems develop pink to rust colored near the base stem. The plant grows in tufts. Its leaves and stems die back after the first frost in winter but they reproduce easily in spring from the underground rhizome system.

Spread

• Johnson grass spreads rapidly through farmland, vineyards, roadsides, orchards and where land has been disturbed for construction. Its U.S. Department of Agriculture hardiness zone is not identified but it is described as an agricultural pest in most states south of the 42nd parallel. It competes with agricultural crops for soil nutrients, sunlight and water, thus reducing crop success. Johnson grass is sometimes mistaken for barnyard grass (Echinochloa crus-galli) or Fall Panicum (Panicum dichotomiflorum) before its distinctive pyramid-shaped flowers develop. Neither of these two grasses is identified as an invasive species. Native plant species have natural biological controls in their ecosystems that prevent them from invading other plant species.

Eradication

• Johnson grass is not responsive to large-scale applications of herbicides or other single-method control programs. Prevention is the most effective control method in large-scale eradication programs as well as in home gardens. Pull up and destroy the tuber rhizome root systems and all small seedlings that develop around a central weed clump. Thorough tilling brings tough rhizomes to the surface so they can be eliminated. Mowing before the plant is able to develop seeds is also an effective control method.