First a few facts:
I live in California where this state has been in a drought for several years. It can get very very hot here with low summer humidity. We have been on water restrictions the last few years. It's not uncommon for us to be over 100 to 105(F) degrees everyday in July and August for weeks at a time. The hottest I've seen it here is 119(F).
2015:
Last year I did have some Iris die in the heat. I wasn't the Iris fault. Let me explain. I buy some Iris from what I call the local Iris lady. She sells them in bloom or almost in bloom. I usually pot them up and place them in the shade. I've been buying and doing this for a few years. Last year when I bought them I decided to plant some of them. Just a few hours after I bought them the rain was pouring down. Since it was early spring I thought we might get enough rain to keep the ground moist. Of course we didn't get the rain. Just guessing I lost about 1/3 of the planted ones. Due to the water restrictions I didn't give them the water they needed. My fault! The ones I potted up lived.
The Iris I buy from vendors are always potted up and placed in the shade because they are delivered in July or August. I think I've only lost 2 of these in the last few years and they died within 2 weeks of receiving them. They were replaced by the vendor and they survived without any problems.
