You might want to wait until the seed pods just start to turn brown before harvesting--but don't wait too long, or they will open and scatter the seeds. Some people just cut off the entire plant at the base, put the top part with the pods in a paper bag, and then hang upside down until the seeds dry and fall into the bag. Others find it easier to just cut the stalks a few inches below the seedheads, bag them, and hang the bunch upside down that way. The plant is an annual, so after it goes to seed it will not grow back. Once the plant goes to seed, the leaves become bitter and not as tasty as cilantro.
You might want to wait until the seed pods just start to turn brown before harvesting--but don't wait too long, or they will open and scatter the seeds. Some people just cut off the entire plant at the base, put the top part with the pods in a paper bag, and then hang upside down until the seeds dry and fall into the bag. Others find it easier to just cut the stalks a few inches below the seedheads, bag them, and hang the bunch upside down that way. The plant is an annual, so after it goes to seed it will not grow back. Once the plant goes to seed, the leaves become bitter and not as tasty as cilantro.