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Add a soil or mulch berm
A berm (see arrow) should be constructed from soil or mulch to hold water ONLY IF the tree will be watered with a hose or other high volume device. If irrigation will be from a low volume system or if little or no irrigation will be applied, do not bother with the berm. No more water will reach the root ball under these circumstances if a berm is present.
The potential downsides of the berm include cutting off rain water and oxygen when personnel later push the berm over the root ball. Rain and air will have a tough time moving through this soil over the roots. Roots are encouraged to grow when soil is placed over the root ball, and some of these can grow close to the trunk. Some of these could girdle the trunk years later. To prevent soil from being pushed onto the root ball, construct the berm from mulch, not soil.
