Q.Lemon Tree Leaves Wilting
Hello, we’ve planted an ~18″ lemon tree in our backyard about three months ago. We fill the soil “bowl” with water about once a week (once in the morning, once in the evening). We live in Arizona, where our temperatures during the day regularly reach well above 100 degrees. The leaves have started to turn somewhat yellow and wilt. See the attached photos. Are we watering it too much, not enough, or is it something else? thanks!

Certified GKH Gardening Expert
It looks like the soil has quite a bit of clay content. Clay soils need to be amended with organic material, quite heavily, in order to maintain proper moisture balance.
Since it is a bit heavier, you will need to wait longer between watering. Usually, once you are able to dig down 3 or 4 inches without hitting any moisture, then you can water deeply. Watering before this will cause rot, and infections such as this. Sometimes the ground can seem dry, but underneath will still be quite moist.
Planting in the heat of summer is usually not recommended, since trees can easily be overwatered in compensation for the heat, and many plants won't put out roots when it get hot, anyway. It is best to plant these in Spring or Autumn to avoid shock of heat or cool weather.
For now, I would treat with a fungicide for the tops of the tree. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
I would also treat with with IRON SULFATE and DOLOMITIC LIME to treat the soil and root zone. Do this once or twice per year to keep the soil conditioned.
This article will help you to grow Lemon Trees: https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm