Thank you for your question. 

The first thing I notice from this photo is the use of decorative rocks as a groundcover. Rocks can raise the soil temperature and radiate heat long after the sun sets. In addition, depending on what kind of rocks you are using, they have the potential to change the pH levels of the soil, and they also can take away nutrients from the plant. I might advise with the information you gave me to switch from a rock groundcover to an organic mulch. Mulching can improve growth of the tree, improve rainwater infiltration, gives the plant nutrients, and provides shade to the soil.

Use mulch over the critical root zone. 2-3 inches of mulch under the canopy of the tree; do not place mulch in contact with the trunk.