If you grow any type of plants at your home, your backyard may be a gold mine of free seeds. And with a little bit of patience and organization, you can turn those free seeds into free plants, potentially saving you lots of money and trips to the garden center! There are different methods of collecting seed from different plants, and most fall into two categories: dry seed or wet seed.
Dry seed includes veggies like peppers and carrots as well as most herbs and flowers. These seeds must be harvested after they have dried on the parent plant to ensure full maturity. Collecting too soon decreases vigor and germination rates. To harvest, simply pluck the seeds/seedpods off the parent and put in a dry place. For fragile, long-stemmed plants (like dill and cilantro), cut the top few inches off, secure head with paper bag, and hang upside down for at least a couple weeks - all winter if you'd like. The paper bag will catch any seeds that fall as they dry. For seeds that still need separation from plant tissue, allow to completely dry then crumble into a bowl. You can separate the seeds and "chaff" by using a few different methods. Accurately-sized mesh screens capture larger material and let smaller seeds fall through. An angled wooden board keeps the chaff up top while round seeds roll down its surface. And the classically-used technique of "winnowing" involves pouring the mixed material into a bowl from a height that allows the wind (or a fan) to blow the chaff away. (You can also just bounce the mixture in a bowl and carefully blow the chaff away) Once you have the seeds cleaned, package and LABEL. I use coin envelopes from Staples to organize them, writing the type of seed as well as the year harvested on the front. Most seeds can last years if stored properly in a cool, dark place.
As for wet seed (like tomatoes and cucumbers), they become a little more difficult to work with. They must also stay on the parent plant, sometimes longer than "market" readiness, to mature. Consult this handy chart to see when your edibles are ready to be harvested for seed. To properly dry, scoop out the seeds with minimal pulp into a bowl filled with water. The viable seeds will sink, and the dead ones will float. Carefully pour off the bits of pulp and dead seeds, rinse remaining seeds, and repeat several times until no more pulp remains. Then drain into a strainer, pulling off excess moisture by dabbing a towel along its underside. Spread seeds onto a dry glass or ceramic plate and place in a cool, shady spot for several days. The larger the seed, the longer it'll have to sit out to dry. You can tell when they're ready if seeds like squash break instead of bending and seeds like corn shatter when hit with a hammer.
Some wet seeds also need to ferment before drying - specifically tomatoes, cucumbers, and melons. Fermenting can be a tricky (and stinky) process even for the expert gardener, but it helps increase germination rates and eliminate disease pathogens. Immediately after harvesting, scoop seeds into a jar, again, with minimal pulp attached. Fill with about half as much water as pulp and seeds, and set in a warm place (75-85 degrees Fahrenheit) for one to five days. Keep an eye out for bubbling and/or the formation of white mold on the surface of the mixture. Once this happens, leave for 24 additional hours, then continue with the cleaning process as described in the previous paragraph.
When harvesting any kind of seed, take note of the parent plant's health - it's size, vigor, and any presence of disease. Bacteria and viruses can be transmitted through seeds, as they are a systemic infection. Fungi cannot. Healthier plants produce larger, healthier seeds, so harvest only from your best. Not only does harvesting your own seeds save you tons of money; it gives you a deeper sense of pride in your garden. Your plants don't come from starts bought at the garden center anymore. They are yours, through and through. I find the practice almost meditative. Just put on your headphones, pop in some music, and get ready to have an endless supply of your garden favorites!
Hopservatory Manager, NASA JPL Solar System Ambassador