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Restoration efforts in the western US occur across a diverse array of plant communities and climatic conditions. Restoration is likely constrained by different factors in different locations, but few efforts have compared the outcomes of rangeland restoration experiments across broad spatial scales. We compared results from multiple studies to evaluate the roles of water availability, plant-plant interactions, and herbivory as drivers of restoration success across three dramatically different ecosystems: arid sagebrush steppe in north-central Nevada, slightly wetter sagebrush shrublands in northwestern Arizona, and a semi-arid shrubland-grassland ecotone in northeastern Wyoming. At the most arid sites, efforts to directly increase available moisture during plant establishment led to long-lasting restoration benefits. In an eroded old-field, irrigating for two growing seasons led to 6.7 times higher perennial grass cover and fewer large vegetation gaps, even three years after irrigation ceased. In another Nevada study, seed coatings designed to increase available moisture had mixed effects, but were generally beneficial when planted species were grazed during the second growing season. In Arizona, however, seed coatings had negative rather than positive effects. Across all sites, we found evidence that plant establishment was constrained by competition with other, already-established plants. In both the most arid and the most mesic locations, established perennial grasses inhibited shrub establishment. In Arizona, established perennial grasses reduced perennial grass seedling establishment. Plant-plant competition in semi-arid systems may reflect underlying competition for available soil moisture, but few studies have tested this mechanism in a restoration context. Overall, our results suggest that direct manipulations of moisture may be critical for restoration at the most arid sites, and a recognition of competition from established perennial plants is relevant across a wide range of arid and semi-arid systems.