In Australia, Sonchus oleraceus has been emerging as a major weed in conservation agricultural systems. The effect of environmental factors on germination and emergence of S. oleraceus was assessed on populations collected from Gatton (SOG) and St. George (SOS) regions of Australia, which are high and low rainfall regions respectively. Germination of both populations responded similarly to various environmental factors studied. Although S. oleraceus seeds germinated under a broad range of temperatures (15/5, 20/10, 25/15 and 30/20°C day/night), germination was lower at 15/5°C. There was only 47–53% germination under dark conditions compared with 62–87% under alternating light–dark. Germination was only 2 and 3% at –0.8 MPa osmotic potential for SOG and SOS populations respectively, and no germination occurred at –1 MPa. Germination was 6 and 8% at 200 mM NaCl for SOG and SOS populations respectively. Although S. oleraceus seed germination exceeded 80% for pH 6–7, germination was reduced at pH outside this range. Germination was 83 and 87% for SOG and SOS populations respectively at the soil surface; and emergence decreased with increasing depth, with none from seeds buried at 6 cm depth. Wheat residue amount within the range of 0–2000 kg ha^–1 did not alter germination; however, germination was significantly reduced when the crop residue amount increased to 4000 kg ha^–1 and the lowest germination was at 6000 kg ha^–1. The potential to germinate under diverse environmental conditions correlates with the widespread occurrence of this weed in the northern region of Australia. High residue amounts and occasional tillage leading to deep burial of seeds may reduce its emergence and incidence.