When most people buy seeds to plant for a given year, there is usually a date stamp on the packet that says "for 2011". This leads to the confusion that all seeds have an expiration date and cannot be used next year. Not true at all! I have planted seeds that have been around for ten years. But, that is an extreme case and is not recommended. If you have seeds left over from a previous purchase and want to find out if they will grow, there is an easy test for viability. In this case we just want to know that if they are planted normally, will they germinate?
If you have enough seeds to spare, place ten seeds on a folded- over paper towel. In this case there are 10 radish seeds from 2008 that I still have. Fold the paper towel again to cover the seeds and moisten well. Not enough to soak them, but to just moisten. I use ten so that I can have a direct percentage to judge whether or not there is a good reason to plant them. But, if you have fewer seeds, just use two or three seeds. Set the towel in a warm place and continue to moisten periodically for two or three days.
When you open the towel, you should see that the seeds have opened and are sprouting. Of course, they will not grow as there is no nutrient value in a paper towel! In this case, all ten have sprouted and the real seeds can be planted with confidence. It is important to remember that most seeds do not have a 100% germination rate. Some are as low as 60%, but the average is usually around 80%. Bon Appetit!
The author has an eclectic background in chemistry, electronics, writing, mental health, and community action...Ken