Gather the foliage together loosely in your hand once the plant is 6 inches tall but before it produces a seed stalk. Avoid squeezing or bruising the leaves.
Cut through the base of the plant with a sharp knife, cutting the cilantro off at the soil surface. Use the harvested leaves immediately or preserve them for later use.
Prune back 2/3 of the foliage if you want coriander seeds. Cut off the foliage at the base of the plant before the cilantro sends up its seed stalk. Leave the remaining 1/3 of the foliage in place to fuel the cilantro during seed production.
Trim off the seed stalk beneath the pods after they turn brown and dry. Store the seed heads in a paper bag in a dry area. The seeds separate from the pods and fall out once they are completely dry and ready for storage.