what are the difference between old and new seeds
Answers
Most flower and vegetable seeds will stay viable for at least a few years if they're stored at a low enough humidity and temperature. The ideal situation, says the USDA, is a room where the temperature and relative humidity add up to less than 100. Get one of those multi-purpose thermometer and hydrometer sets and find the best room in your house for long-term storage. (Or use it to test the room your seeds have been stored in thus far.)
And there are dates on your packages, Don! They should be stamped "Packed for 2006", or 2007, or whatever year the seeds were sold at retail. Seeds that are only a year old, or slightly older but whose packets are still unopened, generally germinate nicely.
If they're several years old, the packs were opened and/or the seeds were stored in less than ideal conditions, subject them to a germination test. Place some sample seeds inside moist paper towels and slide the towels into a plastic bag. Mark the type of seeds on the front, but don't seal the bag. Let them sit out in the warmest room of your house and check them at day five and every day thereafter. Viable seeds should sprout by day ten. If they don't, or if less than a third wake up, get fresh seed.
In the future, store excess seed in sealed glass jars to which you've added a few of those little moisture-absorbing desiccating pouches that come with vitamins and shoes. (The things that say, "Don't eat me!") And keep the jars in the room that best meets the '100 rule'; not in your always-damp garden storage area.