Some swaps feature classes on growing, seed cleaning and preparation, or other garden-related themes. Some have potlucks, so that local gardeners can meet and greet and discuss their interest in gardening. Some include sharing cuttings or rootstock of outdoor and house plants. There are no rules involved, just a mid-winter fix for gardeners when the weather is nasty and the ground frozen.
To see if there is a seed swap in your area, visit the Seed Swap Day BlogSpot or check the local paper or event calendar. If not, consider gathering some friends and neighbors and starting your own swap. Have some open-pollinated or heirloom seeds on hand, as well as some small seed packets so folks can take some home.
Though there are seed packets available for purchase, you can make little envelopes out of old newspaper by folding over and taping or gluing the edges and also creating a top fold. These will keep the sunlight out and provide a dry storage for seeds.
Leftover vegetable seed, if less than two years old, can also be brought in to share. Though seed viability decreases over time, free is free and if it sprouts, perfect. I tend to collect more flower than vegetable seed, harvesting my annual or perennial seeds, as well as seed from native plants. One plant that I easily harvest each year is common milkweed because of its monarch butterfly connection. I sow some of the seeds in the garden and let them do their thing. The others I sprout in spring and transplant seedlings.
Harvesting and cleaning seeds takes a little patience and time. Depending upon the types of seeds, whether they are dry or wet, will dictate the process to follow. You don't want to use seeds from hybrid plants, only those that are self or open pollinated. A seed packet will tell you which of these the seeds are from. Also, if you grow different varieties of squash, melons, cukes or other Cucurbits, you'll want to make sure they are far enough apart, like a mile, so there isn't cross pollination. The sprouts from these seeds will turn out weird.
Tomatoes are self-pollinating so different varieties can be grown in close proximity and the seeds harvested. Just make sure the parental plants are not hybrids. Peppers and eggplants are like the Cucurbits, but don't need such far separation. Cross pollination for them could also turn out some odd next generation plants.
Dry seeds are ones from carrots, onions, beans or herbs like basil. They can be spread on newspaper or crumbled onto a screen where the seeds drop between the mesh onto another surface. You can separate seeds from chaff by dropping the crumbled pods onto a slanted piece of cardboard or wood and let the seeds roll down away from the pods. However you separate the seeds, you are just cleaning them of chaff, leaves, debris or other plant material that got mixed in with the collecting. Let the seeds dry for a day or two to remove any excess moisture, and then store them in air tight containers. Putting in a little silica gel or one of those moisture absorbing packets from vitamin containers will help to draw out any extra moisture.
Though it is preferred to let the seeds mature on the plant, they can be harvested prior and then dried. For wildflowers like lupines or bee plant, I wait until the pods barely open, then collect them and separate out the seeds.
Wet seeds are those that are surrounded by pulp, like tomato, squash or pumpkins. The best way to clean these seeds is in a colander with running water and working the seeds until there isn't any pulp left attached. This is more work, obviously, but a really good way to get a fair amount of seed from heirloom plants. Dry the seeds on a ceramic plate or glass plate, not paper towels; the seeds will stick to paper.
Tomato seeds have a gelatinous covering and it is removed through fermentation process. To ferment the seeds, place them in a bowl with any pulp and add water that equals about Ω of the original mixture. Set the bowl out of the way, it can get rank, and let the seeds ferment for several days. A light colored mold will start to form on the surface, and when this coat gets really thick or bubbles start to rise, add water to double the mixture and stop the process. Stir the mixture and let settle, then pour off the water and goo and any seeds that have floated to the top. The viable seeds will settle to the bottom. Repeat the process to get the best seeds. Pour off the last water through a colander and shake the colander to remove as much moisture as possible. Spread the seeds on a plate, not paper, and stir them several times a day to get even drying. Though this process has to happen relatively quickly, for wet seeds could germinate, don't dry them in an oven or put them on a sunny shelf. Once dry, store the seeds in a container.
But even if you don't harvest and dry your own seeds, the swaps are a great way to meet other gardeners, learn or share things about gardens, and become aware of issues surrounding the production and harvesting of seeds.