We have a lot of great 9b real estate in this country in parts of Arizona, Texas, and Florida. So it should be no surprise that we see all kinds of amazing Ceroxylon and Rhopalostylis, huge Dypsis decipiens and......oh wait......what? You mean these won't tolerate the heat? So......in this country these will only grow in places where it doesn't get that hot? like coastal California? Where it doesn't get cold enough to take advantage of all that cold tolerance anyway? What a rip.

We get super hot here in the summer, and my Rhopies do fine. I think the key is that it cools down at night...we can be 105 in the day, and it still gets into the 60s at night. Never seen an ounce of heat stress in my Rhopies.

California 9b > Florida 9b

Florida 10b >>>>> California 10b

(For palms, that is)

Well there is heat, and then there is heat plus humidity.

I think your right Xerarch.

I have a feeling that there is a heat limit these palms can take. And I think its just above 105. My rhopie looked worse every time we would get some high heat. My D. Decipiens didn't begin to really decline until we started having high humidity in August.

Agreed! There are a handful of nice palms that can survive AZ cold but not our heat. Very disappointing.

I think it's worthwhile to point out that heat is about sustained high temps over long periods, and not just daytime highs but also nighttime lows. Sure a Rhophie can survive 100+ in California, just like a Coconut can survive 35 degrees in Florida. I don't know how much a role humidity itself plays, but I do know that humid climates tend not to cool down as much at night, adding to total heat. Whatever the reason, the above mentioned species do not perform in areas with truly warm summers.

Add Jubaea too, Sunset lists them as viable is sunset zone 13, that's Phoenix, ya right. Jubaea does ok in Dallas but forget Houston or Florida. Sustained high temps without nighttime cooling is a killer.