I think their actual hardiness is closer to 10a but I could be wrong. I've seen the pair at the Huntington in LA. Agree that it is one of the world's most amazing tree species in terms of bark. That being said Arbutus menziesii is right up there, too. Pity they are dying out, even in parts of their native range. And of course they are completely impossible to grow on the east coast, along with 'Marina'. There's an Arbutus X andrachnoides at Woodlanders in SC, and I'm hoping mine survives this winter. Didn't protect it and it has about 25% leaf burn now, but it's small and I generally find its performance encouraging. Certainly, this was not a winter that zn 8 plants were going to survive w/o almost complete top kill. My pineapple guavas now appear completely dead, although after the first freeze to 3F they only had about 40% leaf burn. What's really emerging this year is that the duration, repeatedness and depth of the freezes are almost as bad as the absolute temperature reached, at least for many warm temperature/subtropical plants.

I live in central Phoenix. I planted two of these at the end of April/beginning of May of this year (2015). I got them from Ebay from a Nursery in Florida for less than $50 including shipping. They were both 3 foot tall skinny sticks with no leaves when they arrived. 7 months later they both got top heavy so I had to thin them both. One of them is just under 6 feet tall and the other one is over 7 feet tall. They survived the intense summer heat with no problem, which was awesome considering not planting them at the best time of the year. We've had a couple nights in the upper 30's so far this winter, and they are fine. Only concern is if we have a hard freeze which we have every couple years. I put tree/mulch rings around both of them to help retain water and hopefully help in case of a freeze, but will take additional measures if there's any real threat. Hoping these become huge shade tree's soon! I don't expect them to get as huge as they would in their natural habitat, but I still put them in a big open space, far away from my property and any sort of structure. The trunk and leaves are both red and green right now; they look very festive. I don't like evergreen tree's in the winter other than pine, but I just had to give these a try.

Also some near the stadium there in San Diego. There's a reason they aren't commonly planted in southern California; they are fairly frost sensitive while young, being more tropical than their Australian species they also aren't drought tolerant, and if not planted as young seedlings, very subject to wind throw in Santa Ana winds. They also get very very tall. For all these reasons, they aren't an ideal choice for most residential gardens.

If that is what yours is the bark is pretty colorful, other seedlings from the same cross may be quite different in this aspect of course.