We have had a couple of hot days lately and I started wondering whether figs prefer hot or cold feet. All my plants sit in black pots, placed in a greenhouse and I noticed that for some reason at least a couple of them, the Noir de Barbentane and the Madeleine DDS were not showing much signs of new fig development.
Off course, inside the greenhouse, the temps easily climb to 110F, so it must be stress on the roots as well, especially inside a black container. Watering was never a problem, the root system never dried out.
As I moved the stressed plants outside, I noticed that the fig development speeded up, the pots were moved in a very sunny place all day long.
Is this prove enough figs prefer rather cool soil then very warm soil? I read somewhere on the figs4fum website that pots have to be covered with dark plastic to avoid water loss and to keep the roots a few degrees warmer, but I start to believe the contrary is true.

Could this also mean, considering my observations are correct, that too much temperature swings during spring time could well be the reason why potted figs often drop pretty much all of the early figs?

Covering to raise the temps is a winter task. In the summer you are mainly going to be cooling the roots. Ideally the root zone should be around 75 for optimal development. If I left black pots under full sun the soil temp would hit well over 120 easy. 

How can one cool down the nursery black pots while keeping the figs in full sun? I felt my pots hot to the touch and thought this is surely not good for the roots.

Looks I will be protecting the pots from the sun from now on. When you think it through, makes total sense.

You can protect a couple ways depending on which direction the sun hits the pots from. If it's only from one direction, as is my case, you can put up shade cloth so the leaves get full sun, but the pot doesn't. Otherwise people have had success with wrapping a a cheap car sun-shield around a pot.

You want the roots to escape and forage for nutrients. My fastest grower last year was half buried.

There was a study published some short time ago (I don't have the URL handy but i think it was mentioned previously in one or both forums) about the effect of painting pots in keeping root balls cool.... They used white (shiny and flat), Silver, green, brown colors for their testing. If I recall correctly, the White painted pots were the coolest with some small differences between shiny and flat white and Silver was also fairly effective but not as good as white. green less so and brown negligible. Might be of interest to look up the research again. Someone suggested painting pots cheaply, quickly and easily with a roller and glossy white latex paint.... Aluminum foil might also work well and considering how cheaply it can be had at the dollar store, it might be another alternative to re-potting into white containers....

The last two years, I went to the dollar store and purchased silver auto windshield reflectors to wrap around my larger sized pots. For a buck, they did the trick. Smaller pot I burned the bottom two thirds. As mentioned earlier, drain holes should be on the sides of the pots. It makes it much easier to dig out the trees when they go dormant.

I spray paint my pots with white paint. When ambient temp is about 90 F, a black pot can be 120 F at the surface facing the sun. (C.E. Whitcomb, Plant Production in Containers)

Experiments do have their use in trying to find the ideal growing conditions. Thx