I cannot answer for desert climates, but I have found that if you have early morning sun until 2/3 o'clock in my zone 7, you can grow almost anything. I unfortunately have mostly shade with afternoon sun which I think is the worst...no sun in the morning and then things get blasted with hot afternoon sun.. With afternoon sun of 5/6 hours you can have roses, vegetables, etc, but there is NO comparison for full all day sun for those kinds of things...

I was reading a book by Larry Hodgson called "Making the Most of Shade." Although I didn't agree with everything in his book, I was intrigued by what he called the "Petunia test." The test involves planting petunias here and there in the shade garden to see whether they'll bloom. He said that if a petunia will bloom even weakly in an area, then that indicates a part-sun situation. He suggested using the test to determine whether some plants might bloom in an area that's thought to be shady.
I live in Colorado, where sunlight is more intense than it is in other areas of the country. I thought I would give the petunia test a try next spring to determine just how much sun I get in various areas of my shade garden. You might consider doing the same in your area before investing in more expensive plants that require at least part sun.