Answer: You can harvest dry seedheads whenever they appear. Wait until the seedheads are mature, but not so mature that they split open and spill their seeds. Each plant is different so you'll have to watch them carefully. When you think they're ripe (when the seed head is brown, not green) cut each seedhead off into a white envelope and seal. Label, keeping each variety in a separate envelope. When the seedhead is completely dry, it will open and release the seeds into the envelope. You can check them to make sure they're really dry, and then store them in an airtight container in a cool, dark place until it's time to sow them next spring.
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