Technical Abstract: Cover crops are important components of crop rotations on organic farms and affect soil quality, nutrient cycling, and pest and disease management. This study compared cover crop light interception, cover crop biomass production, weed biomass production and weed seed production in several winter cover crops including two cereals (rye and oats), a mustard mixture, and two legume/oat mixtures. The cereals were planted at two densities and the other cover crops were each planted at a single density. Light interception differed markedly between the different cover crop treatments especially early in the season and increased with cover crop density. There were significant differences in cover crop biomass production that changed over the season. By the last harvest date, the legume/oat mixtures and rye at the high seeding rate has produced significantly more biomass than oats at the low seeding rate and mustard. Weed biomass production was highest under the legume/oat mixtures, and significantly more chickweed seed production occurred under these mixtures than under all of the other cover crops. The data suggest that increasing the seeding rate of the cereals and adding more oats to the legume/oats mixture reduced chickweed seed production.