For germination, the seed requires moisture, heat and oxygen and as a fourth, some seeds especially fine, small seeds, also require light, like lettuce for instance, but that’s not the case with all seeds. But all seeds do need moisture, heat, and oxygen. If you restrict those, you can store seed for long periods and the classic way of doing that is to keep seeds dry. And they need those because those are critical to the respiration process. It kicks off growth in the little embryo inside the seed.
If you want to save seed for next year for your garden, so long as you keep them dry, like ten percent moisture,even if it’s at room temperature just keep them dry and you will be able to keep your seeds until next year and most of them are going to germinate so just keeping them dry is the first important step to storing seed.
But if you want to store them even longer, you can put them in a cold situation so you remove and reduce the heat. Dry seed put into the freezer,it’s going to store a long time and if you really want to store it for decades– I don’t mean you at home, but for national seed storage banks,for security reasons you can store seeds and in the vapor of liquid nitrogen and extremely cold temperatures for decades.
Oxygen can also be restricted in order maintain seed saving longer so if you go to a seed storage repository like the USDA Seeds Lab in Fort Collins, Colorado where they have a huge warehouse of seeds from all over the world, they keep them in foil pouches that have been evacuated of oxygen and they keep them dry and they keep them under cold conditions and the seed stores for a long time.
The point is, those three are important in getting seeds to germinate but if you restrict them you can also save seed for a long period of time.