It's easy to get carried away buying seeds as winter wanes. Sometimes we end up with too many seeds for the space in the garden and set them aside, intending to plant the seeds when we have room. Last year's seeds can become the-year-before-last year's too easily. Most packets are marked for the year in which you should plant them; this is the time when most of the seeds will germinate successfully. Seeds as old as 200 years have germinated, however, so your packet of 2-year-old seeds should have a good chance.
Put your seeds in the vegetable bin of the refrigerator for a few days to simulate cold winter days. Remove 10 seeds and sow them, according to depth directions, in potting soil in a pot or half a milk carton on a sunny windowsill--or on a damp piece of paper towel in a plastic bag. If more than a few plants sprout, the packet is probably good.
Sprinkle the seeds into a bowl of water and wait a few hours. The seeds that sink are viable and will probably germinate. In fact, they sink because their embryos are beginning to "wake up" and take on water. Skim the floating seeds off the top of the water to discard or plant in a trial patch.
Add an even mixture of compost and humus or manure to your garden soil before planting. Cultivate well, digging the amendments into the top 6 inches of soil.
Plant your seeds according to spacing directions in the prepared garden. Cover seeds lightly unless directions state to leave them uncovered--some seeds (like morning glories) need light to germinate. Mark planting lines or spots with frozen dessert sticks to keep track of the names and locations of your old seeds.
Make a note of successes in your garden notebook. Although American seeds are often marked for use within a year, European producers may mark some of the same varieties as viable for 5 to 10 years. Keep your own record for future reference.