I'm planning to grow out all of my container trees in 15 or 20 gallon Gro Pro nursery pots with an irrigation system.
They will be on a wood platform near the brick wall on the south side of our home.

From what I've read the optimal temp for roots is 77f. I'm sure it varies by plant but in general that might be a good target temp.

I could see the soil temp getting higher than that in a container. Maybe not I don't know.

Has anyone measured the soil temp in a large nursery pot in the sun ??

This will be one of the variables I will monitor this summer

Rich,
Greenfig did an experiment last year and posted his results.
There has been a lot of published information on optimal temperatures for plants, attached is a document with non technical explanations.

greenfigs test shows that the temp will go very high in middle of the day. once the temp goes above 90 down here, i usually water my trees twice a day, once left out in the sun. i water in the morning using drip system almost everyday, and if the leaves are drooping and stressed, i water them again to cool them down. they usually perk up quick. 

Hi RichinNJ,
How about shading the pots so that they don't get the sun ?
You could throw some mulch over the pots, or make a plain wooden fence all around the pots - if they are grouped of course ...

Great info. Thanks.

Looks to me like the south facing brick back of our house will be way too hot for plants in containers if they are left there the whole summer. It might be good to put them there in the spring and in the fall.

For in-ground trees it might be a good location.

Ill have to find a different place to grow the figs I have that are in containers during the summer.

"Pot in Pot" might be a solution but it looks like alot of work for 20-30 plants.

http://www.uky.edu/Ag/CCD/introsheets/potinpot.pdf

Painting the pots a light color will help.  I use a pale green.  mulch the tops of the pots or plant ground cover grass/flowers in the pot.  I'm going to do that this year.  I'll also be setting up a drip system for watering a couple of times a day.

http://www.utextension.utk.edu/mtnpi/handouts/Beginning_in_Nursery/Comparision_of_Production_Systems.pdf

You can also clothespin (looks tacky) shade cloth to the pots and that will help keep them cooler.

Suzi

Shade the pot with anything; cardboard, hay, etc. Paint the pots white, cover with aluminum foil, double pot, or plant in ground. All will keep the soil cool. I've never seen damage even when I haven't taken these measures but it can't hurt to provide a little shade.