cover plants at 37-40 degrees?

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45 and under for more than 30 minutes can kill pepper plants, I've done it. I wrap them if its under 45 at midnight.

If peppers died at 45 degrees, than I wouldn't be able to grow them here at all. The lows here are in the 40's usually until July, and my plants go out at the end of May. Check out my growlog and you'll see that I am able to grow peppers just fine. It is true that they don't put on a lot of new growth at those temperatures, but mine certainly can survive. It is very dry here, plus the sun is more intense at higher altitudes, so maybe that makes up for the low nighttime temps?