A growth model is needed which will account for time of planting and stage of growth for annual grasses and for time of season and harvest interval for perennial grasses. A linear intrinsic growth function was assumed previously which described response of dry matter accumulation to harvest interval for a warm‐season perennial. Field data indicated that this model was appropriate for intervals up to about six weeks. Beyond this range yields peaked and then declined with increased interval. This article assumes a linear‐exponential intrinsic growth function which more accurately describes the data and removes the restriction on harvest interval. The model describes dependence of dry matter accumulation on time of season and harvest interval for a warm‐season perennial Coastal bermudagrass(Cynodon dactylon). Mean time and standard deviation of the distribution are independent of harvest interval. The model also accounts for time of planting and time in the season for the warm‐season annual corn(Zea mays)as related to dry matter and plant nitrogen (N) accumulation. The resulting analytical functions can be used to estimate values on a pocket calculator without need for finite difference procedures.