Plant essential oils and their components are used to protect stored grains against insect pests. Cereals and grain legumes are stored for future use as food and seed for further propagation. Phytotoxicity of four essential oil components, carvacrol, 1-8-cineole, eugenol, and (-)-menthone, to cowpea Vigna unguiculata (L.) Walp was tested at 10 and 20 µl/L doses. Effects of these oil components on seed germination and seedling growth parameters (i.e., shoot length, number of leaves, moisture content, root-shoot ratio, root length, root volume, root surface area and length of root hairs) were determined at 1, 2, 3, and 6 months after fumigation. Differences in germination and seedling growth between fumigated seeds and unfumigated seeds (control) were used as indices of phytotoxicity of the oil components. Generally, phytotoxicity of the oil components to cowpea seeds was dependent on dose, oil components, and storage period. Seed germination and seedling growth were negatively affected by carvacrol, 1-8-cineole, and eugenol at 2 and 3 months after treatment. 1-8-cineole was the most toxic while (-) - menthone was the least toxic component to cowpea seeds, irrespective of dose and storage period. Higher germination and seedlings growth of 1-8-cineole-fumigated seeds were obtained at 6 months compared to 2 and 3 months, suggesting possible biodegradation or degassing processes. This study showed that carvacrol, 1-8-cineole, and eugenol reduced cowpea germination and seedling growth. In addition, germination of seeds fumigated with essential oil components and presumably natural essential oils, does not imply that the germinated seeds are viable.