Aloe species commonly flower during the winter dry season in southern Africa and produce abundant dilute nectar. We investigated variability in nectar production and availability in Aloe castanea because evaporation is more likely from its open flowers than from the tubular flowers of most other Aloe species. The greatest variability in nectar production was associated with flower age, and weather conditions and individual plants also had significant effects. However, when unscreened flowers of similar age were sampled throughout a clear day, nectar volumes and concentrations were remarkably constant, and concentrations did not exceed 10% w/w. Variability in concentration could be reduced by reabsorption of sugars, but there was no evidence of reabsorption after addition of relatively concentrated nectar (26.6%) to flowers. It appears that rapid secretion throughout the day accounts for the constant low concentration.