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Each flower bud will produce a seed pod containing many flat, black seeds. If you want to harvest the seed, wait until the pods dry completely on the plant, then cut off the entire stalk and break the pods open to collect the seeds. Be sure to watch them closely so they don’t pop open and spread seeds everywhere’s.  Crush the pod to remove seeds. Overwinter, keep seeds in moist sand in the refrigerator.

There may be more information on the internet.  I’ve never done this so good luck.