According to the tag it's supposed to be hardy to zone 5 but I have seen plants from another grower and they look a little different so I think there may be two forms circulating in the nursery trade, one that is smaller and more cold hardy, and one that is larger and isn't as cold hardy. I have the smaller version.
I got the plant this spring and planted it in a hole with a little pea gravel at the bottom and with paver base around it. It has grown quite a bit and has been really happy, even with recent upper 90's temperatures.