Tomatoes, peppers, beans, and peas are great choices for plants to save seeds from. They have self-pollinating flowers, as well as seeds that don’t require any special treatment before being stored. But they’re not the only choices, of course. I’ve successfully grown melon seeds I’ve saved. I’ve also saved sweet potato tubers to plant again next year (which is technically a tuber, not a seed, but it’s still the same basic idea).
Plants with separate male and female flowers, like corn and vine crops, can cross-pollinate. As a result, it’s hard to keep the seed strain pure for these crops. For example, sweet corn can get pollinated by popcorn in a nearby garden on a windy day. This will impact the flavor of the resulting corn, and the ears “will be neither good sweet corn nor good popcorn.”
Aside from corn, cross-pollination doesn’t typically affect the quality of the current crop, but it can affect the quality of the next generation of crops whose seeds are saved from the current plants.
When you save seed, be sure to choose open-pollinated varieties, rather than hybrids. Open-pollinated varieties produce offspring that are similar to the parent plant. On the other hand, hybrids produce offspring that aren’t necessarily similar to the parent plant. Hybrid seeds can contain any combination of the good and bad traits from the parent plant.
When you store the seeds over winter, store them in a tightly sealed glass container. You can store more than one kind of seed in the container, if you keep the different varieties of seeds in separate paper packets, while storing them all in the container. Keep the seeds cool and dry. A refrigerator is a good place to store them. Also, be sure to write down the crop name, variety, and the date you saved the seeds, and be sure to use the seeds within one year after you save them.
If you’re saving tomato seeds, then the best thing to do is to put the seeds and pulp in a jar to ferment before removing and drying. If you simply squeeze the seeds out of the fruit and let it dry, many of them will grow, but you’ll have a better germination rate if you allow the seeds and their pulp to ferment before drying the seeds.
I hope this helps you get started with seed saving. Good luck!