In order for seeds to remain viable over long periods of time certain variables must be controlled. Temperature, humidity, exposure to UV light and oxygen all play a crucial part in determining whether or not your survival garden will be a success or failure. I have been selling survival seed banks for about a year now. Our seed banks are hermetically sealed in a tough Mylar pouch. This pouch is impermeable to UV light, oxygen, and moisture. Our seed banks our held in a temperature controlled environment prior to packing and shipping. The seeds in our survival seed bank will remain viable for 7+ years if properly stored in a cool dark place until ready to use. A refrigerator or freezer is best and can extend the life to 10+ years. But you must understand that the longer you store the seeds before planting the less they will sprout. That is where seed saving from year to year comes in handy with open pollinated seeds. But honestly there really is no definable limit, as was recently proven in Israel with the successful germination in 2005 of a 2,000 year old seed of the extinct Judean Date Palm that came from an archeological dig at King Herod's palace near the Dead Sea. In 1978, a 12,000 year old Lotus seed discovered in a dry lake bed in China was also successfully germinated, which prior to the Date Palm was the world's oldest successfully germinated seed. More recently, the Millennium Seed Bank successfully germinated three species of plants from 200 year old seeds. Recently (February 2012) Russian scientist announced they had regenerated a narrow leaf campion (Silene stenophylla) from a 32,000 year old seed. The seed was found in a burrow 124 feet under Siberian permafrost along with 800,000 other seeds. Seed tissue was grown in test tubes until it could be transplanted to soil. This shows how long DNA can be viable in the proper conditions.
You can get more info from our website, myseedcellar.com or the link below.
http://www.http://myseedcellar.com/seed-faqs/