Onion grows under a wide range of climatic conditions but mild season without great extremes of heat or cold or excessive rainfall is best suited. It requires a temperature of 12-25°C before bulbing and 15.6-21.loC for bulb formation. The plant is somewhat hardy and can withstand freezing temperature. It can be grown as a rainfed crop at 1500 to 2100 metres elevation between April and August. In places where the annual rainfall exceeds 25 to 100 cm, the onion does not thrive well. It requires 70 % relative humidity.  Exposing plants to very low temperature in the beginning favours bolting and hence the transplanting of seedlings before 15th of December (plains) is never recommended. Likewise sudden rise in temperature favours early maturity of the crop which results in small sized bulbs. Thus, delayed transplanting after 15 January is also not desirable as the plants are exposed to high temperature.