Beans (Phaseolus vulgarisvar Mwezi Moja) were grown in the field under two irrigation levels (irrigated and rainfed), two nitrogen levels (no fertiliser and 100 kg N ha−1) and two planting densities (22 and 44 plants m−2) at Sonning (UK) and Kabete (Kenya). The crop duration in the three experiments was 114 days in Sonning, 95 days in K1 and 73 days in K2. Irrigation increased total dry matter early in the season at Sonning but had no effect at Kabete experiments because of high rainfall in K1 and ‘ineffective’ irrigation in the drier K2 where most of the water was lost through evaporation.