Experiments were conducted to evaluate the effects of seed scarification, temperature, light, salt and osmotic stress, and pH on seed germination, and also the effects of seed burial depth on seedling emergence of Sida rhombifolia. Scarification with sulphuric acid released seeds from dormancy and stimulated germination; though germination of scarified seeds was not influenced by light. Seeds treated with sulphuric acid for 120 min resulted in 65% germination compared with 5% for non-scarified seeds. The response to scarification indicates that a hard seed coat is the primary mechanism restricting germination. In two separate experiments, a concentration of 111 mM sodium chloride and an osmotic potential of -0.49 MPa reduced maximum germination (64 to 65%) of S. rhombifolia by 50%. Germination was not influenced by the pH of buffered solutions ranging from 5 to 9, and it varied from 60 to 65% over this range. Seedling emergence was greater than 60% at burial depths of 0.5 to 2 cm, but decreased thereafter, and and no seedlings emerged from the seeds buried at 8 cm. The results of this study identify some of the factors enabling S. rhombifolia to be a widespread and problematic weed in the humid tropics and provide information that may contribute to its control