This study aimed to investigate whether different doses of specific phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, -hydroxybenzoic acid, syringic acid, vanillic acid, and -coumaric acid), alone or in combination, can inhibit the early growth of the common ragweed ( L., Asterales: Asteraceae). A seed bioassay was performed in Petri dishes and placed in a climate chamber to assess the effects of five dose levels of phenolic acids to radicle and shoot length, as well seedling biomass of . The lowest dose of phenolic acid corresponded to the natural phenolic acid concentration previously reported in dry plant tissue samples from Brassicaceae cover crop plants. Results show that the inhibition of the early growth of depends strongly on phenolic acid. Across different treatments, high doses of phenolic acids significantly shortened shoots and radicles, as well as reduced seedling biomass. Treating seeds with ferulic acid alone, vanillic acid alone, -hydroxybenzoic acid alone, or a mixture of all phenolic acids significantly reduced all early growth parameters. The estimated effective dose for the 50% inhibition (ED ) of radicle growth in seedlings was 368.39 ± 59.85 × 10 mol with ferulic acid, 135.41 ± 17.65 × 10 mol with -coumaric acid, 810.36 ± 134.15 × 10 mol with -hydroxybenzoic acid, and 160.11 ± 12.30 × 10 mol with the combination of all phenolic acids.