Annual grasses are difficult to control in sweet corn in Canada due to the scarcity of registered herbicides with grass activity. In addition to the potential soil health benefits, over-seeding living mulches into the cropping system may help sweet corn growers improve annual grass control by increasing competitive ground cover. To test this hypothesis, trials were established at three locations in Ontario and Quebec, Canada, in 2008 and 2009. At each location, sweet corn was over-seeded at the 4–6 leaf stage with one of three living mulches alone or in combination with an herbicide. The living mulch/herbicide pairings were adzuki bean (linuron + S-metolachlor), cereal rye (saflufenacil), and oilseed radish (pendimethalin). All living mulch treatments were compared with an untreated control and an industry standard (S-metolachlor/atrazine). When sweet corn was over-seeded with living mulches alone, the most effective annual grass control was provided by the cereal rye. The least effective living mulch was adzuki bean, but the combination of adzuki bean plus a herbicide was the most effective for annual grass suppression. The final marketable yields in all living mulch treatments were always lower than the industry standard. In spite of effective annual grass control, reduced yields may make the adoption of the tested living mulch species less attractive to conventional sweet corn growers.