Wait until the cilantro plants bolt and the seed heads turn brown and dry
Cut the seed heads from the plant
Place the seed heads in a paper bag or on a clean, dry surface
Let the seed heads dry completely for several days
Rub or crush the dried seed heads gently to release the seeds
Separate the seeds from the chaff and plant debris
Store the seeds in an airtight container in a cool, dry place
Label the container with the harvest date