Although duration of irradiance did not affect flowering of 128-d old plants, flower numbers increased when plants were grown under 45% SH, especially when given during the 21–40 d period.This suggests that irradiance should be reduced to 45% for 20–40 d beginning 21 days after sowing to increase flower number on plants with 4 pairs of leaves. The increased number of flower buds when irradiance was reduced by 45% in January, when natural irradianceis already low, suggests that low irradiance is responsible. However,it is possible that some flowers may abort under low irradiance. This hypothesis should be further evaluated by checking the rates of flower development and flower abortion under a microscope after production at low irradiance levels.