I do not remember exactly, citrus roots do not function well at about 85 - 90F. Over, 100F will kill the roots. I suggest you shade the pots, paint them white, or wrap in aluminum foil.

Putting trees in larger pots risk root rot because the trees cannot remove water from the soil fast enough compared to trees in a smaller pot that holds less water.

Where do you live? I need to get my infrared thermometer and go check all my pots too after reading the original post. By noon, my new growth is already wilting and the pots are damp. I guess the heat from the concrete patio and brick walls of the house is bouncing onto my trees. Never thought to measure how hot it really is out there. I just know that I don't like being out there either. Half of my trees are in 20" pots and the other half are in 14". I am in the process of finding new locations for them to have afternoon shade as we are going to be in a heat wave of upper 90*s for the upcoming week.

Denise, I use my wife's digital kitchen thermometer which has a probe attached to it by a cord. I stick the probe into the soil. Where in the pot you put it affects the reading. The closer to the wall of the pot, the hotter it will be. And, of course, the side that gets the sun will give the highest reading. I suggest you put the probe near the pot wall exposed to the sun to get the worse case scenario.

Be sure to let the probe sit until the readings do not change much.