How long will seeds last past the "expiration" date on the back of the packet? Can I use 2008 seeds for next year?
Disclaimer: I am no expert, and there are many others on here that will give you their experience based on years of proven trials. I have just one season to back up what I'm saying :)
I got seeds from the seed exchange forum, several of which were from 2004 and everything I planted grew. In fact most of these "older" seeds did better than some of the "new" store bought seeds. Certainly that could be a variety thing and not necessarily the seeds, but hey, if it grows, I dont care how old it is.
Worst case scenario is you plant them and they dont grow. Nothing to lose (I'd personally have a back up plan, so that my entire garden plans were not a flop if in fact they dont grow :)
I think most of this year's seeds will be viable next year. I've planted some from 1999 and they came up fine. I test them before planting by folding 10 seeds up in a damp paper towel then putting it in a warm spot like on top of the fridge. Keep it damp but not soggy and after a few days you'll see how many germinate. This will give you a rough percentage of the number of viable seeds in the packet. You can then increase the seed density accordingly when you plant them.
The 2008 date is really an expiration date, it is a "packed for 2008". When stored properly (cool and dry conditions) most vegetable seeds except onions are viable for several years. I have some 5 and 6 year old seeds that I still get better than 70% germination from. Some have reported tomato seeds germinating after 10-15 years.
Check out the FAQ on this over on the Seed Saving forum for details on how to save and store.
The reason there is an expiration date is that before the seeds were pkged. to be sold, they were tested for germination. Veggie seeds need to have a certain percentage of germination or they can not be sold. The percent varies depending on the type of veggie but the percents are pretty high.
Viability of seeds drops when improperly stored, and there's no guarantee of how well a seed saved by a store to sell a year later might do. Also there are a few types of seeds that will only be good for a year, chives and onions for example.
Most seeds though like tomatoes when stored properly in a cool dry place, will still germinate at a very good rate for at least 5 years.
The 2008 date is really an expiration date,
Sorry I meant to say it is NOT an expiration date. ;)
I agree with what others have said. Below is an article about proper seed storage. There's also a chart giving general guidelines for how long seeds last. It's a general guide. After all scientists were able to get seeds from the tombs of Egypt to germinate!
Here is a link that might be useful: Seed storage
I store my seeds in a tin box in the fridge and use them for several years, but if in doubt, I put 10 seeds in a folded wet paper towel, into a plastic bag, and put in a warm, unlit spot (unless they need sun to germinate). Count how many germinate and if it's 7 or more I use them.
To all of the good information already given, I will add just a couple notes.
As others have mentioned, the date on the seed envelope is not an expiration or "use by" date. However, neither should commercial seed be assumed to be fresh seed from the previous year. As long as the company's seed continues to meet the minimum standard for germination, they will continue to sell it... so the storage life listed in Booberry's link may not apply to commercial seed.
Home-saved seed, if properly dried & stored in a cool, dark location, can easily exceed the shelf life given in the CSU bulletin. Frozen seed can last even longer... but control of proper seed moisture is more critical.
Also, if you know you will not be planting all of your seed, it is best not to take it all into the garden with you. Exposure to humidity (paper envelopes placed on the ground) or excessive heat (left in direct sunlight) can shorten the life of the seed very quickly.
If you must bring all of your seed to the garden, I recommend that you use a small portable cooler to protect the seed, and remove what you need just prior to planting. Use no ice, though... even if the seed had been stored refrigerated, it should be allowed to reach room temperature prior to planting.
If you intend to save short-lived seed (such as onions) for next year, frozen storage in heat-sealed foil packs is the preferred method.
Side note: if you use inoculant for your beans & peas, keep it in a cooler also. It is extremely sensitive to heat & sunlight.