Although outcomes of hybridization are highly variable, it is now considered to play an important role in evolution, speciation, and invasion. Hybridization has recently been confirmed between populations of yellow (or common) toadflax (Linaria vulgaris) and Dalmatian toadflax (Linaria dalmatica) in the Rocky Mountain region of the United States. The presence of hybrid toadflax populations on public lands is of concern, as both parents are aggressive invaders already listed as noxious weeds in multiple western states. A common garden experiment was designed to measure differences in quantitative (shoot length, biomass, flowering stems, seed capsule production) phenological (time of emergence, first flowering and seed maturity) and ecophysiological (photosynthesis, transpiration and water use efficiency (WUE)) traits for yellow and Dalmatian toadflax, F1 and BC1 hybrids, as well as natural field-collected hybrids from two sites. Genotypes were cloned to produce true replicates and the entire common garden was also replicated at two locations (Colorado and Montana); physiological data were collected only in Colorado. All genotypes grew larger and were more reproductively active in Colorado than in Montana, and hybrids outperformed parent taxa across vegetative and reproductive traits indicating heterosis. Hybrids also emerged earlier, but did not flower or set seed sooner than parent taxa, and all genotypes set seed more quickly in Montana than in Colorado indicating a strong environmental influence on this trait.