Johnsongrass | Photo: University of Kentucky's College of Agriculture

Life Cycle: Perennial
Origin: Eurasia
Poisonous: Yes

Johnsongrass is a coarse-textured perennial grass that grows well in pastures, landscape beds, gardens, fields, and roadsides and is highly competitive for soil water in these sites. This weed was introduced into the southern United States as a forage grass, escaped into cultivated fields, and subsequently invaded other sites. Johnsongrass is robust and can reach heights of 10 feet under good growing conditions. Individual leaves can be between 10-25 inches long, and the root system is fibrous and dense.

Johnsongrass reproduces from seeds and underground rhizomes (creeping rootstalks). Seeds germinate most readily at soil temperatures above 65 degrees, while the rhizomes will begin growth at temperatures less than 60 degrees. Each panicle (flower cluster along the stem) produces several hundred seeds, which will remain viable in the soil for more than 20 years. The rhizomes can reach several feet in length and persist for three years or less under Kentucky conditions. Prolonged cold periods (less than 15 degrees) can kill rhizomes, especially if they are on the soil surface