I am getting together a seed supply from an heirloom seed company and have bought seeds in bulk from the local Co-Op. What is the best way to save the seeds and what should they be stored in?
Dry, cool and out of light- I usually keep mine in a plastic box in the fridge. There may be some that shouldn't be cold or something but I have kept seed good for years doing this.
Different seeds have different viability- there sre published lists of length of storage and best storage methods- I think Seed Savers has such a list.
"seed supply" as in for planting this spring? Just leave 'em in their original sealed packages til you're ready to use them, and keep them somewhere not too hot (this time of year, just don't leave 'em on the car dashboard or on a furnace vent and they'll be just fine ) Once opened, store airtight and cool, preferably with a humidity-absorbing sachet to keep them dry.
if you mean "seed supply" as in stocking up for future years of uncertainty, you need to think that through a lot more carefully because only some seeds store well for years. You need to look up tables of storage times and decide what's best for you depending on what you're likely to be able to grow and want to eat. Really all your stored seeds should be rotated through every few years -- grow them out and save new seed to store for a few more years -- and with poorly storing things like carrots you don't really have a lot of choice.
As a *partial* (very partial) alternative, you could store large quantities of seed, because even if a particular plant's germination rate is only 5% after, like, 10 years, if you have ten thousand seeds it'll still give you some actual plants
I will add to what patandchickens said with - you can use powered milk as the moisture absorbing agent -
I store my seed in the original package in a canning jar in the fridge. (Actually 3 jars right now).