Understanding soil seed-bank dynamics of endangered species is crucial for their effective management and conservation. Whether or not seeds of Harrisia fragrans Small, a U.S. endangered cactus endemic to Florida (USA) form persistent soil seed-banks or withstand drying and/or freezing under storage conditions was unknown. We conducted a seed burial experiment with seeds collected from three sites (North, Middle, and South) within the Savannas Preserve State Park, FL, USA. We buried the seeds in plots with three light conditions (sun, partial sun, and shade) at each of the three sites and tested their viability in germination trials after 3.5, 8, 11, 16, 19 and 23 months of burial in soil. Buried seeds remained alive throughout the 23 months of the study period with germination ranging from 64 to 100%, which suggests that this species forms a persistent soil seed-bank. Microhabitat conditions markedly affected seed-bank size and subsequent seed viability. Seeds from the South site exhibited higher and faster germination than seeds from the Middle or North sites. We also evaluated if H. fragrans seeds could withstand dry storage under low relative humidity (RH) and low temperature. In the laboratory 76% of seeds stored under 12% RH and -20°C for 1 and 24 weeks germinated faster than seeds stored under 21–23°C and 50% RH. Thus, the capacity of Harrisia fragrans to form a persistent soil seed bank influences population persistence. Its ability to be stored in orthodox ex-situ conditions offers viable options for its future conservation and regeneration.