Plant development is highly malleable, as evidenced by the ability of cultured cells, tissues and organs to regenerate into whole plants in vitro. The ability of plants to regenerate in vitro is influenced by many different factors, including the donor plant growth conditions and the type of explant. Empirical trial and error manipulation of these and other culture parameters is the basis for improving plant regeneration protocols, but the mechanisms underlying the effects of these parameters on plant regeneration are unknown. Somatic embryogenesis (SE) is a type of in vitro plant regeneration where somatic/vegetative cells are induced to form embryos. Here we show that seed maturation is one of the parameters that affects the ability of germinating embryos to undergo auxin-induced somatic embryogenesis in Arabidopsis thaliana. Late maturation stage seeds harvested from yellow siliques have a higher capacity for somatic embryogenesis than seeds harvested later from brown siliques, a process that can be mimicked by post-harvest storage. Physiological and genetic analyses suggest that an oxidizing environment and ABA metabolism enhance the rate at which germinating embryos lose capacity to reactivate embryogenic growth. Our data suggest that there is a narrow window during late seed maturation in which embryogenic competence is reduced, and that this process also takes place, albeit more slowly, during seed storage. This knowledge provides a framework for identifying new plant totipotency factors and for directing efficient SE in systems that make use of mature seed explants.