The easiest seeds to save are open-pollinating, nonhybrid annuals. Plants that are not self-pollinating can cross-pollinate; therefore, it is best to grow only one variety of a plant from which to save seed. If two varieties of spinach bloom near each other, the resultant seed is likely to be a cross between the two. Different varieties of peppers should be separated by 500 feet to avoid cross-pollination. Melons, pumpkins, cucumbers, and squash need even more personal space - at least a half-mile.
Biennials require more work and commitment, as they do not send up seed stalks until the second season. Biennials include beets, Brussels sprouts, cabbage, carrots, cauliflower, celery, onions, parsley, parsnips, rutabaga, Swiss chard, and turnips.
Do not save seed from hybrids if you want plants like the parents. Seeds from hybrids produce a mix of offspring, which may have different characteristics than the parents'. Seed from hybrid vine crops are often quite variable, also squashes, cucumbers, melons, and pumpkins often cross-pollinate with other genetically compatible varieties. Unless pollination has been strictly controlled, strange hybrids often result.
Among the vegetable seeds most easily saved are nonhybrid tomato, pepper, bean, cucumbers, and summer squash. Collect seeds from fully mature, ripe fruit of these plants.
Tomato: The seeds are encased in a gelatinous coating, which prevents them from sprouting inside the tomato. Remove this coating by fermenting it. This mimics the natural rotting of the fruit and has the added bonus of killing seedborne tomato disease. Squeeze the seeds from a fully ripe fruit into a bowl, add water, and let stand at room temperature for about three days. Once fermentation occurs, mold will form on the surface of the water. Add more water, stir, and then gently scrape mold and debris off the top. Repeat until only clean seed remains, and then strain, rinse, and leave the seeds at room temperature until dry.
Peppers: Select a mature pepper, preferably one that is completely red. Cut the pepper open, scrape the seeds onto a plate, and let the seeds dry in a nonhumid, shaded place, testing them occasionally until they break rather than bend. Leave at room temperature until completely dry. Beans, peas, and other legumes: Leave pods on the plant until they are "rattle dry."
Summer squash: Summer squash is at the seed-saving stage when you cannot dent the squash with a fingernail. Cut it open, scrape the seeds into a bowl, and then wash, drain, and dry them.
Storing seeds: Store most seed in airtight jars. The exception is legumes, which store best in breathable bags. To keep the seeds dry, fill a small cloth bag with about one-half cup dried powdered milk. Place the packet in the jar beneath the seed packets. Label your container with the variety, date, and other information. Store your seeds in a cool, dark, dry place; a refrigerator is a good choice. Avoid opening the container until you are ready to plant. Stored seeds will retain their viability for different lengths of time. Melon seed can be stored for as long as five years, while sweet corn is only good for one year. Other types of seed remain viable for two to three years.