Let zinnia flowers fully mature on the plant
Wait until the flower heads dry and turn brown
Cut the dried flower heads from the plant
Place the heads in a paper bag or on a dry surface
Let them dry completely for several days
Break apart the dried flower head
Remove the seeds from the petals and chaff
Keep only the plump, dark seeds
Store the seeds in a labeled paper envelope or airtight container
Keep the container in a cool, dry, dark place