Seeds from Setaria faberi, S. viridis and S. pumila panicles in three Iowa crop fields were collected for the entire reproductive period. Seed number, panicle length, and seed number per panicle length varied among species, panicle types and sites. Greater numbers of seed per plant and per panicle were observed than previously reported. Setaria seed rain exhibited some stable, and many more plastic, responses. S. faberi panicles were consistently longer than those of S. viridis. S. viridis parameters were greater than S. pumila. Earlier panicles were greater than, or similar to, later ones for all parameters. More typically, tillers and panicles responded to local conditions in a plastic way, confounding the formulation of seed production generalizations. In S. faberi and S. viridis no consistent relationship between seed number and panicle length was observed among different tiller types. A more consistent relationship between parameters was observed for S. pumila compared to the others, making prediction possible for this species. The stability and plasticity of these relationships is partially due to the differences in S. faberi and S. viridis panicle, fascicle and spikelet morphology compared to S. pumila. These stable and plastic responses provide fine-scale adjustment to a locality, maximizing exploitation of local opportunity.