We have described here some Aguaruna Jivaro beliefs related to root crop horticulture and the various means Aguaruna gardeners employ to promote the successful development of their crops, particularly sweet manioc. Because it is their major source of carbohydrates and the main ingredient of the beer that is indispensable to the traditional system of feasting and hospitality, manioc has an extremely important role in Aguaruna society. There is a tremendous demand for manioc in the household, but available evidence suggests that gardens easily produce enough tubers to satisfy this demand and could even generate a surplus with little additional effort. Nevertheless, the Aguaruna themselves perceive manioc production as highly uncertain. They feel compelled to increase the chances of an adequate crop by using magical techniques to encourage plant growth and development. These techniques include the establishment of harmonious communication with the souls and spirits of the garden, the strategic use of images (especially those embodied in the metaphorical language of songs) as a fecundating force, and the harnessing of the animistic power residing in special stones. As far as we have been able to determine, the notion that horticultural success is uncertain has its origin in Jivaroan world view, not in an empirically verifiable scarcity or unpredictability of garden production. The Aguaruna gardener feels that technology alone cannot guarantee an adequate supply of manioc and other tubers; and as functionalist theory predicts she responds to this situation through recourse to the supernatural. However, the stresses associated with Aguaruna horticulture are the result of cultural rather than natural realities.