We get asked this a lot. The answer is - it depends. It depends on the seed, on the packaging, and the conditions the packets are stored in.
To start with, we need to be clear that we expect you to sow your seed in the same growing season you buy them in. We have this in mind when we test the seed and date the seed packets, and you should expect good germination in this case. But seeds are living things and you will not get such good results if you forget to plant them for one season and leave sowing them until the following year.
We now supply our seeds in two types of packaging, plastic bags and paper envelopes. The paper envelopes are much better environmentally as they just compost - we hate being responsible for hundreds of thousands of plastic bags dumped in the environment each year.
Different species of vegetables have very different seed life, ranging from the Liscari Sativa which we only sell from harvest til the following spring, because by the summer the seed will be dead, through to melons, where some older gardeners swear by using 5 year or older seed because they believe it gives more fruit.
The table below gives a very rough indication for the most common vegetables of potential seed life, if they start out really good and dry (not just room-dried)
Do be aware that the way in which seeds are stored will affect their life – the following times assume that the seeds have been stored somewhere cool, dry and dark. If seeds get damp or are kept in warm conditions they will keep significantly less well. You'll only reach the top end of the seed life shown below if the seeds are really dry and kept somewhere in an airtight sealed packet (not paper) that stays at a steady cool temperature.
Also, germination is not an on/off state, what will generally happen is that as seeds get older the percentage that germinate will start to drop off, and then at some point will fall to zero.
LIFESPAN OF PROPERLY-DRIED SEED:
If do you have an old packet of seeds, and wonder whether they are worth sowing, you can always test their germination yourself.
Put a couple of layers of damp kitchen towel on a saucer, sprinkle a few seeds on it, and wrap it loosely in a plastic bag (so that it stays damp but is not airtight). Put the saucer somewhere warm - an airing cupboard is ideal – and check after a few days. If your test seeds have germinated, then you are fine to go ahead and sow the rest, sowing more thickly if only a proportion of them grew. If nothing is happening, then you need new seeds.
The other thing that we continue to see year after year is people who come to us worried about social breakdown and who want to buy large amounts of seed to store 'for an emergency'. But this really doesn't make sense! Yes, we know there are lots of websites out there selling 'survival seed packs' but to be honest, they are just preying on people's fears, and its really not a good use of your money at all.
Firstly, seeds are best sown fresh. Even stored in a fridge or freezer, the germination percentage and vigour will reduce over time, often quite quickly.
More importantly, suppose you do find you're in a nightmare situation where you suddenly need to grow your own food - it will be too late to start learning then! Even as an experienced gardener it can take several years to clear a new plot and make it properly productive.
And its not just learning to grow the food, you'll need to learn to save the seed, and store the veg overwinter. All take several years experience. So if tempted by one of these 'survival packs', just picture yourself hungry, standing there in front of your powerless defrosting freezer , with your now-out-of-date seeds in your hand. How exactly does that help you?
So, our view is this: Yes, we are living through the biggest theft in history - as the richest 1% of society turn gambling losses of private banks into public debt to be repaid by the rest of us, the taxpayers. Yes, it is outrageously unfair that our schools and hospitals are closed and privatised so that more money can be given to the bankers. And yes, coupled with climate change and peak oil, the current food supply and economic situation is pretty precarious. So, yes, we agree that it might well be wise to be a bit concerned at this point.
But if you are worried about the future, just stashing seeds away really won't help you. The best thing to do is to start your garden now, while you have spare time and money - and start learning now to grow veg well on your plot, maybe try to learn about storing it without electricity overwinter, and - even better - learn how to save your own seeds for future years. Perhaps your new skills won't ever be needed, but even so, you'll have had fun learning, and not lost anything.
The alternative, of just buying a pouch of seeds and bunging them in the freezer, is of course much easier, but will actually achieve nothing, other than enriching some doom-mongering seed seller somewhere.
There's lots of information on how to save seed on our website here, plus we also sell (at a reduced price) Sue Stickland's book Back Garden Seedsaving, which will tell you all you could ever need to know about seedsaving.