I am in the mediterranean clima zone with very hot days in the summer. Is it worth or advisable to cover de soil with some clay balls to prevent water waste and water evaporation? I have noticed that the upper part of the soil has dried out but the roots are still damp.
Yes any form of inert media(inorganic) will benefit you greatly. Perlite is also a good substitute and is white to reflect more light also reducing heat in root zone and evaporation. The perlite is cheaper as well. Happy Growing!!!
A couple of layers of "shade cloth" around the base of your plant works well and won't blow away (like perlite) and is the cheapest option too!
As a bonus, it does not stop water or get washed away either.
Regards, Organoman.