What is the best sowing time for castor? The best sowing time is immediately after the first rains of the rainy season . The optimum time in Nigeria and most West African countries is as from April/May of every year. The best time for sowing in Africa for rain fed planting is after the first rains of your rainy season. For more information on this and other details about sowing castor seeds in Nigeria and across Africa refer to an experienced and practiced Agronomist with a background on castor seeds farming.