Experiments to evaluate the optimum sowing date for okra (Abelmoschus esculentus) sown in monoculture or in mixed stands with cassava (Manihot esculenta) were sited on free-draining sandy loam soils in southwestern Nigeria. Okra was sown at the end of July, in mid-August and early September as a late-season crop in 1999 and at the end of May, in early June and at the end of June as an early-season crop in 2000. It was sown at seed rates sufficient to achieve final population densities of 33000 and 40000 plants/ha in late-season crops (1999) and early-season crops (2000), respectively. The late-season crops had shorter growth duration, received less rainfall, and experienced cooler temperatures during establishment and the early vegetative stage, and warmer temperatures during the reproductive phase than the early-season crops. Intercropping had no significant effect on the growth and tuber yields of cassava, or on phenology (i.e. time to vegetative growth, flowering and fruiting) and pod yield of okra in both seasons. However, it reduced weed growth by 35–57%, and kept both the soil and canopy environments of cassava cooler by 2·3–5·8 °C and more moist by 15–30 g/kg, compared with monoculture. The phenology and pod yields of the early- and late-season okra in both cropping systems were dependent on sowing date, indicating that okra production is only suitable at particular sowing dates in both seasons. July-sown okra in the 1999 late-season and May-sown crop in the 2000 early-season took progressively the longest time (i.e. 3–10 and 2–5 days, respectively) to flower and fruit, but these crops controlled weeds and modified the cassava environment better than the rest, and gave the highest fresh pod yields and economic returns. It took okra pods longer to reach marketable size in the late season than early season (i.e. 5–9 v. 2–6 days). It is concluded that the optimal sowing date to attain maximum pod yield and economic returns from late-season okra is July or August and from early-season crop is May or early June. Bearing in mind financial constraints and production costs, the optimal season target for maximum edible pods is the early season and for maximum economic returns is the late season.