Not knowing where you're located or how hot it gets there makes it a little harder to offer advice, but......

When temps climb past 85F shade-cloth may not be enough. I've used micro sprinklers to keep greens from bolting early in the august heat.
Succession planting, choosing varieties carefully, mulching to keep the soil cool, misting and shade cloth........
That's all I can think of.

-Mark

I am in Indiana, we had a broccoli plant bolt since yesterday, it had not developed a head larger than a quarter.

Soil temp is still in the 60s

Amazingly though the beans I put in under black plastic sprouted in 4 days!

Rio_Grande, where are you at in Indiana? From your name, I expected Texas.

I'm not surprised about the beans, especially under black plastic.

I am in Se indiana

I was really impressed, first year using plastic and drip irrigation. I am loving it already. We are near Dearborn county.