This paper presents a model for the photosynthetic growth of C 3 green plants, consisting of a 1-periodic scalar first order nonautonomous ordinary differential equation, of the generalized logistic type. The model is tested both mathematically and experimentally. For a very large biologically significant range of the parameter values, the equation has a repelling trivial solution and a unique positive one-year-periodic solution, which is globally attractive from all positive initial data. Biomass production predicted by the model matches field data.
