Petunias grow either as a ground cover or as individual plants. They grow well in flower boxes, hanging baskets, flower beds and many other containers. Some have a few large blooms while others have many smaller blooms; some have single-petaled and some have double-petaled flowers. This plant grows as an annual, so in order to keep them around next year you must collect the seeds. Knowledge of how to do this will give you numerous seeds for next year.
Let some of the flowers die on the stem instead of deadheading them back. Watch them as they become dried and brittle.
Pinch the faded blooms behind the base of the flower right after they dry completely but before the seed pods split open. Be careful as you pinch them off as they may burst open with handling.
Split the pods open if they aren't split already. Shake out the seeds into a paper bag. Fold the top of the paper bag down to keep the seeds safe inside.
Store the bagged seeds in a cool, dry area. Replant the seeds indoors 10 to 12 weeks before the last frost date.