Biointensive agriculture (BIA) is a suite of small-scale agricultural practices that include the use of high-density mixed plantings. It has been promoted to gardeners and resource-limited farmers as a sustainable organic vegetable production method that makes efficient use of land, water, and other resources. Certain crop mixtures are popularly recommended for use in BIA systems (e.g., tomato, Lycopersicon esculentum Mill., and basil, Osimum basilicum L.); others are discouraged (e.g., tomato and Brussels sprout, Brassica oleracea L.). Rain-fed BIA gardens were planted in 2001 and 2002 to compare land-use efficiency of pure stands and two-crop mixtures of tomato, basil, and Brussels sprout. Brussels sprout was the most competitive crop among the three tested, accounting for at least two-thirds of the land equivalence ratio (LER) in mixtures; basil was the least competitive component crop, accounting for less than one-third of LER. Mixtures made more efficient use of land than pure stands only in 2002, which was hotter and drier than 2001. Potential land-use efficiency of mixtures was likely underestimated in both years because the method commonly recommended for calculating inter-plant spacing in BIA mixtures tends to result in lower total density in mixtures than in segregated pure stands, and does not account for different mixture proportions. New recommendations are proposed to address these problems, and are incorporated into a companion planting spacing calculator available for download. Marketable Brussels sprout yield was poor because of excessive heat for the cool-season crop, not because of poor plant growth. The popularly recommended mixtures did not make more efficient use of land than the popularly discouraged mixture.