I agree, once it starts flowering, the taste changes and it is worthless, even if you cut the flowers out, except to let it produce seed. I'm one of those that doesn't like the taste of cilantro leaf, so I only grow it for the seed (coriander) and because the flowers are good for beneficial insects.
I saw this: It isnâ€™t the heat of the air that causes cilantro to bolt, but rather the heat of the soil. So your cilantro will probably last longer if you keep the soil moist and well mulched, and plant closely to shade the ground. I think a lot of those warm areas where cilantro does well are tropical -- warm and very moist. Keeping the plant cut back and harvested frequently may slow down bolting.
https://www.motherearthliving.com/garden ... pring.aspx
dill and cilantro are so easily excited by the weather changes of spring. When days get warmer, nights get shorter and daylight intensifies, dill and cilantro take note. They pay close attention to lengthening days, the strongest cue that summer is coming. The plants rush to fulfill their destiny, which is to produce a good crop of seeds. .... Making a second sowing helps, because seedlings sown in late May or early June are exposed to lengthening days for only a few weeks, when they are too young to care about reproductive matters. Once the summer solstice passes in late June and day length holds steady [and starts declining rbg] , dill or cilantro become much less likely to burst into premature bloom. More importantly, seedlings that break ground after spring has lost its chill are never exposed to the biggest flowering trigger of allâ€”cold, cloudy conditions followed by plenty of warm sun.
So doing a later planting maybe July or Aug should work well, because then daylight hours are declining.
So it seems like as most things in biology when we start looking into it closely, it is complex. Cilantro is triggered to bolt by some combination of warm soil temperature, lengthening daylight, intense sun and especially warm sun coming after the plant has been exposed to cool and damp. The plant essentially has some kind of internal algorithm that relates the factors