The inhibitory activities of the leachates and volatiles from 53 plant species (spices and herbs) were evaluated against lettuce ( Lactuca sativa “Great Lakes 366”) seedling growth using the sandwich and dish pack methods, respectively. With the sandwich method, parsley ( Petroselinum sativum ) showed the strongest inhibitory effect on lettuce radicle growth (77%), followed by tarragon ( Artemisia dracunculus ) (72%). However, caraway ( Carum carvi ), dill ( Anethum graveolens ) (seed), laurel ( Laurus nobilis ), rosemary ( Rosmarinus officinalis ), and sage ( Salvia officinalis ) were the most inhibitory species (100% inhibition of lettuce radicle and hypocotyl growth inhibition at all distance wells) in the dish pack method. Cardamom ( Elettaria cardamomum ) and thyme ( Thymus vulgaris ) also showed strong inhibitory activity (100% for radicle and hypocotyl growth inhibition at all 41 and 58 mm distance wells). The headspace sampling and gas chromatography-mass spectrometry (GC-MS) analysis identified the main inhibitory active compounds as carvone in caraway and dill (seeds), 1,8-cineole in laurel and cardamom, and borneol in thyme. Both camphor and 1,8-cineole were detected in rosemary and sage, and the total activity evaluation showed that camphor was the major inhibitory compound in rosemary, although both compounds played equal roles in sage.