Ask Mr. Smarty Plants

Cordia boissieri (Mexican olive), which also has the common name of Texas Wild Olive is endemic to Texas, which means it is not native to Arizona, and may be in conditions in which it cannot do well. When you follow the plant link above to our web page on this plant, you will notice this instruction in the Propagation Instructions:

"Maintenance: Requires much water to get it established but once established it is drought-tolerant."

From this USDA Plant Profile, you will see that Mexican Olive grows naturally no closer to Arizona than the extreme southern tip of Texas. You did not say how long ago this tree was planted, but transplant shock is quite common in recently planted trees, particularly if they have been planted in what is, for them, an alien environment. If it was planted pretty recently, then we would definitely recommend more water, allowed to drip in very slowly from a hose. The plant also needs good drainage; if its roots are in clay with no compost or other amendments to improve the drainage, the roots may drown in the water it is given.

Pima County, against the southern border with Mexico, is in USDA Hardiness Zones 8b to 9a, while the South Texas area where the Mexican Olive grows natively is Zones 9a to 9b, a little warmer, but probably not enough to make that much difference. It is more likely that lack of water when the tree was being established and possbly poor drainage and/or the wrong soil is causing the difficulty. And, if you planted it in the heat of an Arizona summer, or even fall, transplant shock is almost inevitable.

On the subject of fertilizing, don't. Any plant under stress, and yours obviously is, should not be fertilized. The fertilizer will try to push a plant to grow more profuse leaves, when what that plant is doing is struggling to survive.

From our Native Plant Image Gallery:

Cordia boissieri

Cordia boissieri

Cordia boissieri

Cordia boissieri