The trick with cilantro is to keep it from blooming. Once it blooms (this is called ‘bolting’), you can forget about harvesting any leaves. So keep it watered, grow it in the shade, and look for varieties that are bred to resist bolting, like ‘Santo‘. Cut back an entire stalk to harvest it, rather than snipping off individual leaves, and pinch off the flowers if they do bloom. If you see a thick central stalk emerging, that’s the one you want to cut back.
If you’re growing cilantro for the fruit, which is what botanists call those round seedpods, then of course you might as well go ahead and let it bloom. Generally the term coriander is used to refer to the dried fruits/seeds, and cilantro refers to the leaves. It’s the same plant. To get that dry, woodsy coriander flavor, be sure and let the fruit dry completely until it is brown. The best flavor comes from plants grown in climates with cool, wet summers. If you can find it, get Coriandrum sativum var. microcarpum, which is favored by spice growers who want the fruit, not the leaves.
Because coriander is one of the key ingredients in almost any gin formula, cilantro makes an excellent addition to gin drinks.