A field experiment was conducted during 1994–95 at the Research Farm of the Central Institute of Medicinal and Aromatic Plants (CIMAP), Lucknow, India to study the yield potential ofArtemisia annuaplanted at different times on sandy loam soil in a subtropical environment. Results revealed that the crops planted between September to December produced significantly higher herbage yield measured directly, or after drying compared with that of February planted crop. September planted crop yielded the highest amount of artemisinin. Therefore, the plants established during pre-winter (August-September) weather and allowed to grow through the entire winter synthesized and accumulated more artemisinin than plants established during early (October-November) and late (February) winter periods. The crop planted in November (or the beginning of winter) was found to be significantly superior to a crop planted in August, January or February, both in herbage production and oil yield. The September planted crop yielded relatively less oil than the November planted crop but the artemisia ketone content of the oil of the former was better. It is concluded that the artemisinin content is dependent on the weather conditions, and high yields of artemisinin do not necessarily depend on high dry matter production by the crop. Under northern Indian plains conditions, theArtemisia annuacrop should be planted in September for getting higher artemisinin yield with superior quality of oil as measured by the artemisia ketone content, and in November for obtaining maximum oil yield.