Seed Viability: A seed's ability to sprout and grow.Moisture is the other really big key factor. To get many years of viability out of seeds they need to be dry, generally drier than mother nature naturally gets them. Whereas 10% moisture is acceptable for long term storage of seeds for eating, they should be dryer than this if you expect to get years and years out of them for viability. Four percent moisture seems to be the magic number where extra drying gives no further advantage. Storing seed for long term storage in hot environments makes the moisture content of the seed more critical. Tests seem to show that the higher the moisture content, the faster the seed's respiration rate. In my mind, increased respiration generally shows a lower state of suspended animation and shorter storage life. And again, temperature is closely linked with this.
When we discuss storing foods away for long periods of time we could be talking about a few different things:
1) Storing seed away to protect it's viability: The science behind storing seeds for a long time in order to sprout them later is still somewhat in it's infancy. What's known is there's a lot of different criteria regarding storing different seeds for long term storage. It seems that every kind of seed has it's own unique criteria for long term storage. Some seeds store better in air. Others store better in nitrogen, and still others do better in a vacuum, carbon dioxide or argon. And others seem to be tolerant to all the different gasses. But from studying the material in Handbook 506, two trends emerge for all seeds: temperature and moisture.
2) Temperature: Generally, the colder you store them, the longer the seed will remain viable. For really long storage - such as 5-10 years, it's best if you can keep them frozen. If this isn't an option for you, you should still store them as cool as possible. For example, it would be better to store them in your basement than in the pantry upstairs. And when winter arrives, it's not going to hurt things a bit, as long as your seeds remain below 10% moisture, to take them to the garage, barn, or other outbuilding where they can remain frozen throughout the winter. Just remember to bring them in before the summer heat returns. The viability of your seed will be short lived in a 130 degree F. outbuilding.
3) Storing seed away to protect it's nutritional value: The question sometimes gets ask, "Doesn't protecting seed for viability also automatically protect them the best for nutrient content and usability?" The truth is, this isn't always the case. Take beans for example. The data in Handbook 506 seems to say that it doesn't matter a great deal what the storage gas is for long term viability. Yet the outer shell of beans stored in air over several years lose their quality to soften up when cooked. However, these same 'hard' beans will often sprout just fine. Removing all the oxygen will just about stop the seed's oxidation rate (although it only slows down the aging process) thus retaining more nutrients over time. This is true even if a seed loses its viability. Please see our Storage Life of Food page in the Whole Grains and Foods Area for further information on this subject.