<p>Clay phacelia (<i>Phacelia argillacea</i>) is an endangered plant that is endemic to Spanish Fork Canyon, Utah, USA. To conserve this species, we collected seeds from 10 wild clay phacelia plants growing in one of its two natural populations, which is owned by The Nature Conservancy (TNC). The seeds were propagated in a greenhouse to produce ten half-sibling families, which were arranged into eight randomized blocks. Our goal was to augment the species’ seed production for long-term storage in conservation facilities and for reintroduction back into the wild. We were interested in testing the effectiveness of adding native soil to the pots of our greenhouse-grown plants. Our soil treatment involved adding 30 mL of sieved soil from the TNC’s site to the experimental pots. After nine months, we collected seeds from the mature plants. Whole-plant harvests were done after 13 months to obtain various metrics of growth. Shoot mass was 18% greater for plants grown with the native soil addition compared to the controls (<i>p</i> = 0.041). Additionally, total seed production per plant was positively correlated with shoot mass, total mass, and average basal stem diameter. These findings increase our understanding of the growth and reproduction of clay phacelia and can be used to inform conservation efforts for this and other endangered plants.</p>