Cheatgrass generally germinates in the fall and grows rapidly until cold temperatures set in. When fall moisture is inadequate, it acts as a spring annual. These conditions occur about 1 in 5 years in southeastern Idaho and 1 in 8 years in southwestern Idaho. Spring production may be substantial, but plants are generally dry by early June. The stage of plant maturity is indicated by a change in color.
Plants change from green to purple to tan as they cure.
The purple stage may be induced by a sudden drop in temperature or droughty conditions. Seeds become viable while plants are still mostly green and before they are disseminated.