How to harvest flower seeds: Petunias! This year, our farm team is growing and saving seed from this ‘Old Fashioned Vining Petunia’ for the Seed Savers Exchange catalog. Harvesting petunia seeds requires some careful timing between the time seeds reach maturity to the time the seed pods burst. Leaving the seed pods on the plants too long can also lead to molding or germination in the event of excess rainfall. Watch this video to learn when and how to harvest petunia seeds from Corbin Scholz, SSE