Two experiments, one irrigated and one dryland, were conducted at a site having a seasonally-dry, tropical climate. A range of planting times, with sequential harvests to age 24 months, was used to study cassava growth and yield. Very high yields of 35 to 45 tonnes dry matter per hectare were recorded for the irrigated experiment. Water limitation restricted yields to 15 to 26 tonnes in the dryland experiment. Known or inferred environmental controls of the yield-determining factors of growth rate, growth duration, and partitioning of assimilates to harvest-able organs were used to interpret the results and thus derive general guidelines for the timing of planting and harvesting in seasonally-dry environments.