Organic farming is gaining importance as an environment-friendly alternative to conventional chemical-based farming. Weed control is a major factor limiting expansion of organic production system worldwide. Cover cropping is considered an economically viable tool for controlling weeds in addition to multiple benefits to soil and crop productivity. There is limited research-based information on cover crop - weed interactions. Field experiments were conducted at Hazelgreen and Culman, AL to determine biomass production and relative efficacy of five winter cover crops, Austrian winter peas, canola, crimson clover, hairy vetch, and rye in controlling weeds compared to Control Fallow. The percentage canopy and biomass of cover crop and weeds were determined. At Hazelgreen, the plant stand generally increased for all cover crops except canola and Austrian winter peas as summer approached. The plant stand of canola decreased from 62% in January to 15% in April. In Culman, cover crops had a better stand and therefore, better weed control than Hazelgreen. Weed suppression was 100% in canola and rye which had full canopy cover. Hairy vetch and crimson clover suppressed weeds gradually. Austrian winter peas had low stand (46%) and allowed weeds growth gradually. In Hazelgreen, the dry biomass of cover crops ranged from 0.62 Mg ha^-1 (hairy vetch) to 5.4 Mg ha^-1 (crimson clover). The biomass of the major weed ranged from 0.2 Mg ha^-1 in rye plot to 2.9 Mg ha^-1 in canola plot in Hazelgreen. The weed biomass in rye, crimson clover, Austrian winter peas, hairy vetch, and canola was respectively 21, 7, 2, 1.5 and 1.3 times lower than weed biomass in control fallow. Weed suppression by cover crop was directly related to cover crop canopy and biomass. The study showed the potential of cover crops for effective weed management provided cover crop has good establishment.