Look for the seed pod on the stem directly beneath the withering blossom. Seed pods are approximately two inches long and turn light tan in color when they are ready to harvest.
Pull the pod off the stem. Collect as many pods as necessary for the desired amount of seed stock, as there is one seed per pod.
Slit open the pod along the side, using a knife or the point of a pair of scissors. Pull open the pod to reveal the seed inside. It is approximately one inch long and elongated like the pod.
Spread the seeds out on a paper towel to finish drying. Place the towel with the seeds in a warm, dry room for two weeks.
Label a paper bag with the plant name and the year harvested. Place the seeds inside and fold the top over to seal it. Store the seeds in a cool, dry place until ready to plant in spring.