Pots in the sun: why the roots cook before the plant dries out
You water every day, the soil is even moist, and the plant continues to wilt. What's failing is not the water, it's the temperature that the roots are living at inside that pot. On a balcony, pots get sun from multiple sides and heat up much more than ground soil.
There is a very common frustration on balconies in August. The plant wilts in the middle of the afternoon, you water it right after, and the next day it's worse. You water again, with more water, and within a week it's gone. The usual conclusion is that it needed more water. In most cases there was too much, and what was missing was realizing that those roots had been living at temperatures that no plant can tolerate.
In the ground, the soil protects. The soil works as a huge buffer. The surface heats up with the sun, but just a few centimeters deep the temperature remains much more stable, and that's where the roots are. A pot doesn't have that soil mass to protect it. It's a small volume, with thin walls exposed to the sun from multiple sides, heating up much more than ground soil.
