Hi John I live in SE Arizona 4500 ft elevation June temps 90-95 around 90 the rest of the summer(we have monsoon rains July, August, Sept). My S. greggii grow much better with dappled shade. A big Palo Verde tree supplies shade for most of my plants. I do have perfect drainage.

I always say full sun doesn't mean a whole day of Arizona sun.

limy:
"Sierra Linda" is a greggii that works well in the desert southwest. I have it here.We get above 100 for about 4
months out of the year.My plant is 8 years old so it has had some abuse ie;record rain,drought,2" of snow and heat.
You may want to try S.microphylla var. wislizenii (aka S.
lemmonii) from Arizona.
Art