Saving seeds from any crop that you have grown is a rewarding, easy and forward-thinking practice. By allowing a few plants to reach full maturity, you can save yourself from having to buy seeds next season. Saving seeds from specialty or heirloom plants is especially important, because buying seeds every year can get expensive.
When you have decided to save seeds from your plants, timing is key. Watch your plants and write down when they head or flower, and when they finally begin dropping seed. You will soon have a record that will be invaluable when it comes to knowing when to harvest seed.
Some seeds are grown in easy-to-harvest pods, which can be plucked off the when they begin to dry and allowed to dry completely on a paper towel inside. But some plants have to be chopped off below the flower or seed head and threshed to obtain the seeds, because these plants will often begin dropping seed if you do not get a jump on the process. Look up the common seed-harvesting process for your particular plant if it does not seem obvious.
Some plants require specific methods for seed harvesting. Before storage, you must assure that your seeds are completely dry, and you can do this by spreading them out on paper towels over a cookie rack, to let them air dry fully before storing.
It is ill-advised to store your home-harvested seeds in plastic, because a seed is a living, breathing thing that is merely dormant before planting. Storing seeds in zipper-style bags or airtight plastic containers can possibly kill or sterilize your seeds, causing disappointment when they are planted and do not sprout the following season.
The best way to keep seeds is in paper, like a small paper sack or in an envelope placed in a glass jar with a lid put on it, but not too tight. Your seeds must be kept in a dry, dark place until the next planting season, to keep them alive and dormant.
It is best to keep your seeds cold, in a cellar or cool place, because fluctuation in temperature can damage them. If your seeds are completely dry, you can store them in a freezer until planting, but they must be very dry, or freezing will damage them.
You can also purchase silica from a camera store and seal the seeds in a jar with a packet of silica to assure that they stay completely dry during storage. To reuse dry gel silica packets the next year, they must be dried. You can dry the packets by baking them in the oven at 250° F for 20 minutes.
It is very important to label your seeds before putting them into long term storage. Always write the plant variety, the date of harvest and the date they were placed into storage clearly on the jar or envelope to label and remind yourself what you have and how long you have had it. If harvested and stored carefully and correctly, most seeds will keep reliably fertile and viable for one year.