Abstract Recruitment of Posidonia oceanica from seeds is infrequent owing to the rare and unpredictable occurrence of sexual reproduction. However, in years of high reproductive success, ample supplies of seeds become available in drifting fruit; this could be a useful source of material for seabed restoration. In this study we introduce and combine viability tests and culture procedures for evaluating this material. Three different groups of collected fruits representing a phenological or maturation sequence were tested for seed viability with tetrazolium. We also examined the effects of storage on the germination and development of seedling root and shoot systems. The younger groups showed good (67–86%) germination and survival, with the tetrazolium viability test proving useful for predicting these processes. However, although a strong correlation between fruit and seed weight was observed, higher values of these parameters did not confer greater germination capacity. The seeds of fruits collected late in the season were more developed and plantlet roots and shoots grew faster under culture, but survival after 4 weeks was reduced (40%). Under the conditions tested, viability was highly reduced and there was no final seedling survival following storage.