Climate change has and will continue to rapidly alter natural ecosystems in the future. In response, plastic and behavioral adaptations (such as shifts in ranges and phenology) have been widely noted across taxa. However, the effects of climate change on evolutionary processes, including interspecific gene flow (hybridization), are much less well known. In this study, we experimentally manipulated rainfall with the use of rain-out shelters in the field for one growing season and quantified rates of hybridization between two congeners, Helianthus annuus (common sunflower) and H. petiolaris (prairie sunflower). We found that H. annuus maternal plants hybridized (produced hybrid progeny) more than H. petiolaris maternal plants, with a trend for decreased rates of hybridization with increased soil moisture (when rain-out shelters were absent). The ratio of open H. annuus inflorescences to open H. petiolaris inflorescences estimated rates of hybridization. This study presents a clear example of how the environment could influence hybridization rates.