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Old August 20, 2016   #2
dmforcier
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Location: Dallas, TX
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You're not going to prevent heating due to air temperature, but insulation might delay it until the cooler evening starts to drag it back down again.

Solar heating is a bigger danger, especially with dark pots. I'm using black nursery pots. Currently I use white plastic garbage bags both to reflect sunlight and form an air gap. It seems to work pretty well, but I don't have the intense sun here that you do (I'm in partial shade). Last time I had pots in all-day sun I used black drawstring trash sacks and snugged up the drawstring to keep the bags up. The heavy bags blouse out to give a larger air gap. Worked well.

A consideration is water. My big plants in the big pots would drink a couple of gallons a day, and the cool water - input all at once - probably cooled the pots some. (Just cut a hole in the bottom of the bag to let excess water out.) With an automatic system, is your water heating before it gets to the pot?

Now, a bit of theory on insulation. The best insulation is a vacuum. Obviously we can't do that. So let's look at how heat is transmitted from one place to another: radiation, conduction, convection. Direct radiation is blocked by an opaque shield, but can heat the shield, transferring energy by another means. A simple air gap is very effective in preventing transfer through conduction, but it allows convection. Foam insulation (or leaves) allows (usually) a higher level of conduction but prevents convection. Theoretically, the better solution would be an opaque shield back by an air gap with vents top and bottom to permit the air heated by the shield to rise out of the gap.

Or buy a bunch of tiny little air conditioners.
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