a seed that does not swell or germinate within its established period of viability. A hard seed has a tough impermeable coat, or testa, that does not allow water or air to reach the embryo.
Hard seeds are encountered most often in seed lots of leguminous herbs (clover, alfalfa, sweet clover), small-seeded vetch, and lupine. Their quantity depends on the conditions that existed during their formation and maturation. For example, in years of drought up to 60–65 percent of the seeds produced by red clover and alfalfa are hard. The number of hard seeds decreases after storage, which varies in time for different crops from several weeks to several years. The sowing of hard seeds results in non-uniform germination and sparse plantings. The impervious seed coats may be scarified before sowing to facilitate germination.