Johnson Grass Sorghum halepense

Johnsongrass is an erect, 2½ to 7-foot tall, coarse, herbaceous perennial grass in the Poaceae family thought to be native to the Mediterranean area but is now found in all temperate areas of the world. It was introduced in South Carolina from Turkey around 1830 by William Johnson and planted along the Alabama river as a forage plant. It has since spread aggressively and is considered invasive in many states including North Carolina. 

Johnsongrass is adapted to a wide variety of habitats including open forests, old fields, ditches and wetlands. It spreads aggressively by thick rhizomes and seeds that are produced in the hundreds and can form dense colonies that displace native vegetation and restrict tree seedling establishment. Sometimes this grass invades gardens and both the seeds and rhizomes can be transported and introduced into new areas in contaminated bags of topsoil.

The plant prefers full sun, moist to mesic conditions, and fertile loamy soil. However, this robust grass is easy to grow in a wide range of soil types and tolerates drier locations and soil containing gravel or clay. Most growth occurs during the summer and episodes of hot dry weather are tolerated.  Classified as a short-day plant, it does not flower if the daylight hours exceed about 13 hours per day. 

Control is difficult but herbicide applications applied early summer prior to seed formation and repeated for several years have shown some success.

Insects, Diseases, and Other Plant Problems: No known insect or disease problems. The pollen is known to induce hay fever. In riparian and other areas where Johnsongrass is highly productive, Johnsongrass may promote fire spread by increasing fine fuel loads above historical levels. This plant is listed as a noxious weed in 19 states including NC See native alternatives to the left.