(Photograph = Mammillaria seeds, Photographer Unknown)
Introduction
Generally speaking, there are two types of seeds for storage: orthodox seeds and recalcitrant seeds. Orthodox seeds can be dried, cooled, and kept viable for many years.
The Details
Cacti have orthodox seeds. These seeds can last for years in the wild, perhaps building a seed bank in the soil that germinates in good years. Scientists studied aspects of storing Mammillaria supertexta seed. The goal was to understand storage so that seeds might be kept in freezers against the horrible possibility that the species could go extinct in the wild.
Seeds were dried at about room temperature with silica gel. Moisture content was reduced from about 16% to about 2.3%, and the seeds were stored for six years at −20 °C (approximately household-freezer temperature).
After six years, the seeds were viable and germinated without negative effects. Now, the goal is to save seeds for longer periods.
Additional Reading: Storage of Mammillaria supertexta Seeds
