Harvesting vegetable seeds from your garden this fall begins with your choice of which vegetables you plant this Spring. Choose non-hybrid varieties as hybrid often produce inferior seeds, and do not plant genetically modified vegetables and expect to collect seeds--most GM vegetables do not produce seeds, and it is illegal to collect seeds from those that do. Your best bet is to plant heirloom varieties for seed collection. However, keep in mind that because many vegetables are cross pollinated, you can never be certain what the quality of the vegetables grown from your collected seeds will be.
Allow vegetables to fully ripen on the plant before picking. Most vegetable seeds are inside the ripe vegetables, but there are exceptions. Strawberry seeds are on the outside of the fruit and carrots must be allowed to flower and produce seeds from their flowers.
Cut open ripe vegetables that contain seeds on the inside, such as tomatoes, cucumbers and melons. Remove the seeds and place them in a bowl of tepid water until the seeds sink to the bottom, leaving the pulp floating in the water. Scrape seeds off of strawberries carefully and allow them to soak in water as well.
Use your thumb and forefinger as necessary to separate any seeds still attached to fruit pulp. Discard the pulp and place the seeds on paper towels to dry overnight.
Label envelopes with the variety of the seed and the date collected and then place the dry seeds in envelopes. Stores the envelopes in a cool, dry location where there are safe from rodents and insects until the following spring, when the seeds should be planted.
Peas should be picked after the pod has dried and the pea seeds left inside the dried pod. The dried pods should be placed in an envelope and saved until the following spring.
Allow carrots and onions to flower and allow the flowers to wilt in the garden. Seed pods will appear from the wilted flowers. Once the seed pods are dry and brown, collect them directly from the plant and place into envelopes. Save for the following spring.