Saving one’s own seeds is necessary for self-sufficient food production. We can put plants in four categories: self-prepared seeds, fermented seeds, multi-year seeds, and self-propagators (no seeds). We’ll briefly cover each category but most people will be saving seeds from the first two categories.
Note that you cannot save just any old seed — well, that’s misleading, you can only save “old” seeds. Most new seeds (including those you’d get from vegetables and fruit from your grocery store) are not worth saving because they are grown on hybrid plants. In short, two different varieties of a plant are crossed to give a new hybrid plant with a desirable trait, but the offspring of this new plant will not breed true, that is, its offspring won’t necessarily be like the parent. You should only save seeds from heirlooms or varieties that are known to be true breeders. Also, you should avoid seeds from plants that have cross pollinated. For example, mustard and kale are cousins and they will cross breed (ditto pumpkins and other squashes) and give you a seed that combines the two plants, not usually in a beneficial way.
Self-Preparing Seeds

Many plants give you ready-made seeds: peppers, okra, corn, squashes and pumpkins, lettuces, radishes, kale, and other plants that make a pod or seeds in a dry compartment. These are the easiest seeds to save: let the seeds dry on the stalk or vine. Plants in the squash family can be de-seeded when the fruit is cut up.

Most of these plants can be simply left to bolt (send out a seed shoot) or dry on the stalk. Once dried, the seed pods can be broken open and the seeds collected. The squashes have moist seeds and can be scooped out with a spoon when the fruit is being eaten. Rinse the seeds in a colander and dry them on a piece of newspaper. Be sure to label the newspaper with the exact variety of seed. You will not remember if you save more than one type of seed.

Once the seeds are dry, they can be put in a jar or envelope and labeled.
Fermented Seeds
Some fruits don’t give such user-friendly seeds. Tomatoes, cucumbers, and other fleshy fruits with gelatinous seed coverings fall under this category. By fermenting the seeds, it removes the gooey covering and kills some seed pathogens. Don’t be daunted by fermentation — it’s easy. The fruit gets cut in halves or quarters and the seeds and their surroundings are scooped into a jar. If the seed goop is soupy without adding water, it can be left as is, otherwise pour in a little tap water. Shake it up at least twice a day for three days. At the end of this time, the viable seeds will have sunk to the bottom of the jar. If you do not have much clear liquid, add warm water at this point and give it some shakes to separate the viable sinkers from the floating duds. Draw off the floating bits and then run the sinking seeds through a sieve or screen, giving the seeds a quick scrub.

Set the seeds on a piece of newspaper to dry. Again, write the name of the type and variety of plant. Either let the seeds dry and then scrape them off or move them around as they dry so they don’t stick. Some folks like to leave the seeds dried to the paper and then just tear off bits to plant in the spring. I scrape them all off and put the seeds in a labeled jar.
Check out these resources for more information and stay tuned for part II later this week.
Detailed seed-saving information for many plants
In-depth detail of fermentation process for small or large scale