I've been "sorta-kinda-mulching" using EWC and trimmed leaves. They break down well in the EWC. I've noticed less watering,not much to write home about,but less watering by up to half a day.
Mulch is a must in hot weather, also helps to slow evaporation when it is quite windy.
Don't make the same mistake as I did years back (on a huge outdoor bush), and learn the hard way that pine needles DO drop your soil pH after a few weeks of being used as mulch... one of my biggest losses to this day...
Michaeljordan, I guess you could use polished stones but you'd need quite a thick layer. The important part is to create several layers of air between your soil and the ambient air, which is what will help keep the moisture inside your soil and buffer temps.
Thanks Dorje. Good thinking.
Mulch itself is going to limit the amount of moisture transpired from the soil's surface, so I'm not sure that's a concern.