National Drought Mitigation Center

Season and Timing of Plant Growth

How Do I Know When Grass is in Rapid Growth?

Rangeland plant communities are naturally composed of mixtures of species that primarily grow at different times during the spring or summer. Grasses are classified as cool-season or warm-season species generally based on their growth response to air temperature.

Rapid growth windows of warm and cool season plants

Maximum growth rates of most cool-season (C3) species occur when air temperatures are 65 to 75F compared to 90 to 95F for many warm-season (C4) grasses. Considerable variation occurs in the range of air temperatures over which measurable growth occurs within each season-of-growth category.

Rapid growth occurs in grasses when air temperatures and soil water are simultaneously favorable. Rapid rates of herbage production are associated with stem elongation. Optimum air temperatures differ among species. For example, 50 to 80 percent of the annual herbage production of most species occurs during a 30-day time period for mid- and tallgrasses on semiarid rangeland.

These rapid-growth windows are best defined by growing degree days. The sequence of rapid-growth windows for different species is the same each year; however, initiation of rapid growth may change by one to two weeks as cumulative degree days change from year to year.