To select the best legume cover crop to grow for a given cropping situation, the producer needs knowledge of relative growth rates, N2-fixation and N-uptake rates, and water use for various potential planting dates. Such an experiment was conducted for 2 yr at Mandan, ND, in which 10 legume species were planted on or shortly after the first day of May, June, July, and August each year. Soil and plant samples were collected periodically after each planting date to evaluate rates of dry-matter production, N accumulation, and water use. Potential N2-fixation rate was measured in one season only. For the first 40 to 90 d after planting, large-seeded annuals such as faba bean (Vicia faba L.), field pea (Pisum sativum L.), and soybean (Glycine max [L] Merr.) generally exhibited most rapid growth, N accumulation, and water use (these three parameters were generally closely related for all samplings). With more than 90 d growth, species such as Korean lespedeza (Lespedeza stipulacea Maxim.), yellow sweet clover (Melilotus officianalis L.), and alfalfa (Medicago sativa L.) also began to exhibit rapid growth. One surprising result was the outstanding growth of May-planted subterranean clover (Trifolium subterraneum L.) in one (ample moisture) of the two seasons. For the shorter growth periods, faba bean exhibited good growth characteristics at all planting dates, and field pea was satisfactory at most. July and August planting of slower growing species generally resulted in relatively little growth by the end of the season. In most instances, water-use efficiency was greatest for the May planting, and highest values were often recorded for field pea, faba bean, and subterranean clover. These results identify those legume species best adapted for a given planting date and duration of growth under the climatic conditions of this experiment.