Here in Zone 7's we have a problem keeping cilantro from bolting and going to seed ( coriander ). Cilantro is such a favorite addition to so many of our dishes yet once the small plant is available we have a small window of opportunity before our heat distracts the plant to the reproduction process, rather than the growing process. Of course our interest is in leaves, not seeds, so we have a problem. We can protect the plants by putting them under Elephant Ears with their wide canopy shielding the young plants from the direct sunlight but it's only temporary as eventually the heat wins out and the plant goes to seed with minimal leaves being produced.
One solution is to use an alternative plant that loves the heat we have and, will not bolt, so the popular cilantro substitute is culantro, that's a "u" not an "i". Culantro forms a natural mound and does most of it's growing in the hottest weather we have here, 90's in mid July - August. The leaves are much wider than regular cilantro and far more of them. On the tips of the leaves you will see a small briar type point but it does not cause any problems when eaten although it may look treacherous to some. The plant is used exactly as regular cilantro is used and is plentiful through the heat of our summers. For us culantro is a perennial in our climate so we can look forward to it reviving itself from year to year.