Wait until each of the cilantro's stems reach lengths of 4 to 6 inches. Cut the entire leaf-covered stem approximately 1 to 2 inches above the ground level, paying attention to avoid removing more than one-third of the stems at one time.
Pull or cut off individual leaves from stems left intact on the plant, as an alternative method of harvesting. For optimum flavor, the Washington State University Extension recommends harvesting the leaves first thing in the morning.
Gather the cilantro stems and secure them together with twine if you intend to use the cilantro dried rather than fresh. Hang the leaves upside down in a warm, sunny spot and allow them to dry. If collecting leaves, lay them on a paper towel to dry.
Place the dried cilantro leaves in a zippered plastic bag or airtight container. Freezing the leaves is another option. Place the leaves in a zippered plastic freezer bag and store them in the freezer.
Twist and pull off the seed heads once the cilantro plant turns brown. Don't wait too long to harvest the coriander, or the brown stems will crumble and the seeds will fall to the ground.
Pour the seed heads into a paper bag. Place the paper bag in a dry, sunny spot. Monitor the seed heads over the next three to five days. Over time, the dry seed heads split and the edible seeds fall out.
Remove the small seeds from the bag. Store the seeds in an airtight container in a cool, dry place.