Artemisia annua plants treated with different concentrations of potassium showed increased concentrations in their leaves and total amounts of potassium per plant. Optimal A. annua growth occurred with the application of potassium at approximately 155 mg L21 (equating to 6.9 g K per plant). Potassium concentrations above this did not increase dry matter biomass, and nor was there any change in leaf artemisinin concentration. However, the total yield of artemisinin, per plant, was slightly higher when potassium application was raised from 53 to 155 mg L21, although this increase was not statistically significant. A concentration of potassium in leaves of 2.6% (w/w) at harvest was adequate for maximizing artemisinin yield per plant.