When applied individually, micromolar levels of simple, volatile, low-molecular weight (C5 - CB) ketones, alcohols and aldehydes released by residues of weeds (e.g. Palmer amaranth, redroot pigweed, and nutsedge) and winter cover legumes (e.g. Berseem clover, hairy vetch, and crimson clover) prevented or retarded seed germination in small seeded crops like carrot and tomato, but did not significantly affect cotton seed germination an determined by radicle protrusion. However, the naturally-occurring mixtures of organic compounds emitted by cover legumes did retard cotton germination during the first 72 hours, and several of the more potent germination inhibitors (e.g. 3-methyl-1-butanol, 2-hoptanone and 3-pentanone) identified in volatile mixtures emitted by plant residues significantly inhibited or prevented cotton root elongation during the first 24 - 48 hours of germination. The effects of theme inhibitory volatile compounds were additive.