Petunias are colorful annuals native to parts of South America. When it is time to plant petunias in your garden the local nursery will typically sell small petunia plants. Seeds are another way to start petunias in the flowerbed. Adventurous gardeners often gather their own seeds, instead of buying seed packets at the gardening center. While it is possible to grow petunias from seeds collected from your garden, the new generation may not be as appealing as the parent plant. This has to do with how the parent plant's hybrid seeds were developed and inbred.
Select the healthiest plant from which to harvest the seeds. The seeds can pass on the bad as well as good qualities of the parent plant.
Monitor the flowers and don't cut them from the plant.
Cover the flower head with a nylon sock or a foot cut from panty hose and secure with a rubber band. Do this when the flower begins to wilt. This will protect the seeds from birds and catch the seeds should the seedpod break before you remove the flower from the plant.
Cut the remaining flower head with the seedpod from the plant when the seedpod is brown and beginning to break open. The seedpod is located below the base of the bloom.
Hold the flower head over a paper sack and carefully remove the covering and rubber band. Allow any loose seeds to fall into the sack.
Pinch the seedpod from the remaining flower and place it in the sack. Discard the rest. If you have more than one flower head, repeat the process, adding each of the seedpods to the same paper sack.
Place the sack in a cool dry location and allow the seedpods to dry out for several days.
Break open the dried seedpods (using your fingers) to release the seeds in the sack. Store the seeds in an envelope. Date the envelope and note the type of seeds and any characteristics of the parent plant.