I don't live in Texas, but I know the concrete in front of my house gets warm after dark. I was thinking it was similar to sand. But I'm guessing the crucial thing here is heat retained in the water which evaporates from the plants, and whether that is more significant than the carbon storage in its greenhouse effect.

I lived in Texas (Houston). One of the weirdest things I remember in summer was the crazy 90 degree heat (at least it felt like it) late at night (like 10p)