We examined genotype (G) by environment (E) interactions for fitness in mesic and xeric ecotypes of the self-fertilizing annual grass, Avena barbata and their recombinant inbred hybrid progeny. Fitness was assayed (1) in experimental water and nutrient treatments in the greenhouse and (2) in common gardens in each ecotype's native habitat. G × E interactions were significant in the greenhouse. Nevertheless, the same recombinant genotypes tended to have high fitness across all water and nutrient treatments. G × E interactions were less pronounced in the field, and were driven by the contrast between the uniformly low survivorship at the mesic site in 2004 and genetic variation in fitness at the other years/site combinations. Moreover, the mesic ecotype consistently outperformed the xeric in both field and greenhouse. Several of the recombinant genotypes outperformed the parents in the novel greenhouse treatments, but these genotypes did not outperform the mesic parent in field trials. Indeed, it is only in the comparison between field and greenhouse environments that there was a noticeable change in the identity of the most-fit genotype. The results provide evidence that hybridization can create genotypes that are better adapted to newer environments such as those imposed in our greenhouse experiments.