They are certainly winter hardy but the real question is if they will be bloom reliable, They develop invisible flower buds in late summer or early Fall and then these open in Spring. If you are interested in them solely for the Fall foliage above all else, I would say to try. Otherwise, I would research and look for other oakleaf hydrangeas in the area to compare notes with the owner(s). Ask about bloom reliability, winter dieback, etc.

The smooth hydrangeas (hydrangea arborescens) and Pee Gee Hydrangeas (hydrangea paniculatas) bloom on new wood and that makes their bloom production more reliable. They are usually winter hardy to Zone 3 or so.

I had oakleafs at my other house, they were beautiful and reliable bloomers. I'll think you'll be fine. Even if the flower buds are winter-killed, the foliage alone is worth the price of admission. However, IME they take a couple years to get fully established and require some baby-ing for at least two seasons -- mostly careful attention to watering all season. Once they're firmly established, they're fairly carefree.

ETA: Other house was zone 6.

Oh, I just remembered I did have some oakleafs at this house, which is zone 5b, that did beautifully. I gave most of them away last fall because they didn't fit in with my plan. I have one left and it's doing well. So yea -- you should be fine with them up here, just pay close attention to watering at the outset.

Oh, good to know. Thanks mkx3.

And do not let the soil stay wet for too long of a time as they will catch root rot easily.

Thank you, all! One more question....I was at the nursery this morning and the sign they had with Alice said they grow to 5 or 6 feet. However some websites say 8 - 10 feet. I want a large shrub, 10 ft eventually would be great! Is that the correct size, and would it grow that large in my climate? Thanks!

I had the big ones at my other house. Can't remember if they were "Alice" or "Snow Queen". Whatever they were, they eventually were at least as tall as I am and I'm 5' 5" -- huge blooms, too. Don't remember exactly how tall they were, though.

The larger size would be more likely to occur in milder winter climates or in locations with a longer growing season (which also tend to be those with a milder winter :-)). 8-10' tall and wide is common in my area.........in zone 5b, I would expect the smaller end of the scale.

Yes, over here, established Alice Hydrangeas easily go over my head and I am 6' tall. In Zone 5B, there may even be occasional winter dieback that keeps the size in check.