Technical Abstract: Spore banks for ferns are analogous to seed banks for angiosperms and provide a promising ex situ conservation tool because large quantities of germplasm with high genetic variation can be conserved in a small space with low economic and technical costs. Ferns produce two types of spores with very different longevities: green or chlorophyllous spores and non-green or non chlorophyllous spores. Green spores completely lose their viability in less than 1 year and often in less than a month, while non-green spores can survive from 1 to 60 years at ambient conditions. Storage at 5°C or in conventional freezers (-18°C) provides insufficient longevity for long-term conservation. Our goal in this work is to characterize deterioration rates of spores as a function of storage temperature from several species of ferns and to use this information to predict feasibility and benefits of cryostorage for fern green and non-green spores. Viability, measured as survival and growth, of spores stored at 45°C to -150°C was monitored for up to 4 years. Over this period, viability of green spores stored at temperatures greater than -18°C was completely lost, while no decrease in viability was detected in spores stored at -80°C or within vapor above liquid nitrogen (-150°C). Based on kinetic models of deterioration rate, we expect green spores to maintain above 75% germination for > 50 years in cryogenic storage, compared to less than 5 years in conventional freezers at -18°C. Non-green spores are predicted to survive even longer. Cryopreservation is not only feasible, but is necessary, to maximize spore longevity for long term preservation.