Marshallia legrandii (Oak Barrens Barbara's-buttons) is a critically imperiled perennial herb in North Carolina and Virginia's Piedmont region. We completed a flowering census of this species at 2 of its 3 known populations in 2021, and again at the largest of those measured populations in 2022. We compared flowering density with canopy openness at both sites. At the largest population, we also measured competing vegetation, soil properties, and Oak Barrens Barbara's-buttons density to describe its habitat. Here, we also implemented an experimental augmentation of Oak Barrens Barbara's-buttons to monitor planting survival and growth under different light environments. We found that Oak Barrens Barbara's-buttons can flower under a broader range of canopy openness than previously believed. In addition to light, we found that competing vegetation, soil temperature, and soil moisture are important predictors of flowering success. Survival of augmented Oak Barrens Barbara's-buttons was nearly 90%, and 28–42% of plants bloomed 2 years after planting.