Certified GKH Gardening Expert
Perennial geraniums, also called cranesbill, will produce seed if you don't deadhead the flowers at the end of summer. The seedpods are elongated and start out green, then change to brownish when ripe. It's important to harvest the seedpods before they "explode" or the seeds will be lost to the wind. You can enclose the pods in mesh bags to prevent that from happening. They must be able to get sunlight, however, so nothing opaque. Once you collect the pods, leave them in a dry, warm area till the pods split, revealing the seeds.
Here is how to germinate the seeds: