The germination (i.e. the first emergence of the radicle) of Medicago denticulata Willd., M. confinis Koch, M. tribuloides Desr., and Juncus vaginatus R. Br. under controlled moisture conditions has been examined. Moisture regime was defined by the soil moisture suction (pF). The influences of temperature and light, which would otherwise obscure the importance of soil moisture, have been minimized by comparing the number of seeds germinated under each physical regime with the maximum number germinated for each species under identical physical conditions when suction was approximately zero (i.e. standard cotton wool germination count procedure). The differing water regimes were obtained by using methods common in soil physics – the tension plate and pressure membrane methods – the seeds being in contact with the plate or membrane kept at a constant water suction. Additionally, two soil media, were used with the Medicago spp. It was found that: