Wild mustard (Sinapis arvensis L.) is a widespread weed of the southeastern cropping region of Australia. Seed germination ecology of S. arvensis populations selected from different climatic regions may differ due to adaptative traits. Experiments were conducted to evaluate the effects of temperature, light, radiant heat, soil moisture, salt concentration, and burial depth on seed germination and seedling emergence of two populations (Queensland [Qld] population: tropical region; and Victoria [Vic] population: temperate region) of S. arvensis. Both populations germinated over a wide range of day/night (12-h/12-h) temperatures (15/5 to 35/25 C), and had the highest germination at 30/20 C. Under complete darkness, the Qld population (61%) had higher germination than the Vic population (21%); however, under the light/dark regime, both populations had similar germination (78% to 86%). At 100 C pretreatment for 5 min, the Qld population (44%) had higher germination than the Vic population (13%). Germination of both populations was nil when given pretreatment at 150 and 200 C. The Vic population was found tolerant to high osmotic and salt stress compared with the Qld population. At an osmotic potential of –0.4 MPa, germination of Qld and Vic populations was reduced by 85% and 42%, respectively, compared with their respective controls. At 40, 80, and 160 mM sodium chloride, germination was lower for the Qld population than the Vic population. Averaged over the populations, seedling emergence was highest (52%) from a burial depth of 1 cm and was nil from 8-cm depth. Differential germination behaviors of both populations to temperature, light, radiant heat, water stress, and salt stress suggest that populations of S. arvensis may have undergone differential adaptation. Knowledge gained from this study will assist in developing suitable control measures for this weed species to reduce the soil seedbank.