Global attention on biofuels and the potential for Jatropha curcas to produce biodiesel from marginal land with low inputs has recently created world-wide interest in this species. This paper reports on the water dynamics and productivity of J. curcas in a silvopastoral experiment with Pennisetum clandestinum at the Ukulinga research farm of the University of KwaZulu-Natal near Pietermaritzburg, South Africa. Measurements of daily total evaporation rates during December–February (summer) on clear hot days ranged between 3 and 4 mm d⁻¹. However, due to the deciduous nature of the species, water use was negligible (<1 mm d⁻¹) during winter (May–August). The results have shown that two- to four-year-old J. curcas trees were conservative water users. High oil yields are unlikely due to the low seed production. The best seed yield was in 2009 (348.8 kg ha⁻¹) in the J. curcas only plots. The other treatments (where pasture competition was a factor) ranged between 77.8 and 166 kg ha⁻¹. Data collected on the time taken by labourers to harvest and dehusk the seeds, showed that 1 kg of seed took approximately 3 h to process, suggesting that mechanical harvesting would be necessary to make seed production economically viable. J. curcas showed a low tolerance to pests and was prone to diseases. This significantly increased the input costs for insecticides and fungicides. The South African results are so unequivocal that J. curcas under the experimental conditions does not fulfil the claims that it is a wonder biodiesel plant.