Interest in switchgrass (Panicum virigatum) as a biofuel continues to increase. Yet problems of establishment still plague. Generally, seeding results in very low or no yield during the first establishment year. Literature recommends planting of switchgrass seed at many times of the year, from February to June, or based on soil temperature. Spring tillage of the soil results in a flush of weedy annual grasses that establish from the soil seed bank. Most citations recognize this fact and suggesting an application of atrazine or Simazine at planting. In Mississippi, our attempts to control weedy annual species in seedling switchgrass with these herbicides have been unsuccessful. In 2002, a single planting of switchgrass seed in August resulted in a decrease of emergence of weedy annual grasses. It was suggested that cooling soil temperatures and shortening photoperiod were suppressing germination of warm-season annual grasses. Based on this observation, a study was undertaken to determine optimal seeding date based on establishment and subsequent switchgrass survival and suppression of weedy grasses. Plots were arranged so that sequential monthly plantings of switchgrass seed could be made from April until October. All plots were treated with Simazine which was watered in. Observations on weed germination were made 2 weeks after planting and again at 4 weeks after planting. Switchgrass yields were taken from establishment stands and the subsequent year's growth. The single factor that contributed to the maximum suppression of weedy grasses was rainfall. Significant rainfall occurring < 5 days after planting caused substantial weed suppression. Months with minimal weed biomass at the end of the season, were April and June Highest weed biomass was observed with September and October plantings. Maximum switchgrass yield after 1 year occurred with an April planting date, contrary to the current recommendation of May.