A bit of organic soil of good quality will help keep the moisture up during hot summer days. It will lower the oxygen and drainage so it is a little give and take. You win some and you lose some.
If you do not want to use organic soil, instead place the trees on a tray with gravel or a mat at the bottom. Have some water in it just reaching the bottom of the pots at hot days. Roots are able to grow out of the drainage holes and reach the water too. Used in Japan for that purpose. Placed on artificial grass mats for example. Watering from above as you do normally, and the rest is taken up from beneath. Shouldn’t be wet at all times but adds a better environment and water lasts longer.