Environmental factors have significant implications on the biology of weeds, hence the study of biology of major weeds in a crop, could prove an ecological and economical viable tool for their management. Echinochloa glabrescens, Leptochloa chinensis, Eragrostis japonica and Dactyloctenium aegyptium are the major weeds of direct-seeded rice (DSR) and many other Kharif crops. The effect of temperature, pH and light was studied on the biology of these four weed species under laboratory conditions during the Kharif seasons of 2012 and 2013. Temperature regimes of 15, 20, 25, 30, 35, 40 and 45°C; pH 5.0, 7.0, 9.0 and 11.0 and light period of 0, 3, 6, 12, 24 and 48 hours were evaluated for their effects on germination, shoot and root growth. Conducive temperature for germination of all four-weed species was 35°C except Dactyloctenium aegyptium, which has maximum germination at 30°C. Similar to germination, maximum shoot and root length was recorded at 35°C in all the weed species except E. japonica, for which 30°C was the optimum. Seed germination was observed over a broad range of pH of all weed species; however, it was highest at pH 7.0. Echinochloa glabrescens was most sensitive to a given pH range among all the weed species. Light periods didn’t alter the process of germination, shoot and root growth. Manipulation of these factors at field level could be helpful in reducing the weed pressure in DSR by preventing their germination.