Sowing the seed! It is a practice almost as old as human culture. For many gardeners, it is all things wonderful - a truly precious moment in springtime.
But all the good feelings can vanish in a heartbeat if the seed is old and fails to germinate. All gardeners know that seed left over from one year can be saved to the next. Many people use tiny bottles and keep them in a cool place - even the fridge. Seeds, however differ in their length of unplanted viability.
Generally the following guideline is accurate:
Onion seed - one year
Corn and peppers - two years
Beans, carrots, peas - three years
Beets, pumpkins, squash, tomatoes, watermelons - four years
Broccoli, cabbage, cucumbers, lettuce, cantaloupes, radishes, spinach - five years
However, do not assume that you will have the same amount of germination in a 5 year old pack of spinach seed that you would reasonably expect in a new package. If you are considering using up old seed, it is smart to do a germination test.
People have many ways to do this, but here is the general principal: you will need a piece or two of wet paper towel, a plastic food storage bag and some seed. Wet the paper towel and place onto it 10 or 20 seeds. Fold the towel so the seeds are totally covered by wet towel. Place that in a food storage bag and label the name of the seed, the amount you are testing and the date you started. Seal the bag except for a small opening. Place it in a windowsill, on top of the fridge or some other warm place. Check daily for germination and count the sprouts (keep a record). When 3-4 days have passed with no new sprouts, do the math and figure what your germination rate is. (If 10 seeds of 20 germinated, you have 50% germination and will want to plant heavily.) If you have less than 50%, consider pitching the seed into the compost, wish it well and buy new seed.