I don't know much about it, but I believe it's a cultivar of H. macrophylla which blooms on old wood, so in your zone if you don't protect it over the winter you're unlikely to see very many blooms, the buds tend to get zapped by late frosts in the colder zones. So while the plant itself is hardy it won't bloom much unless you protect it from those late frosts.
Thanks Ecrane... I'm pretty sure it is a cultivar of H. macrophylla(not that I know what that means). I'm assuming it should be planted in partial/full shade? Also, does the acidity of the soil affect white hydrangeas? I don't think it does, but wasn't sure...
If you plant it in full shade it won't bloom as well, they do best with some AM sun (make sure it's not getting sun in the hottest part of the day though, otherwise it'll be constantly wilting on you). White hydrangeas do stay white so you probably won't see too much variation with this one.
Hey ecrane, would too much shade be the reason my aunt's blue hydrangeas won't flower? Or could it be the late frosts? She says her white ones do just fine. I've no idea what cultivar - my assumption would be H. Macrophylla "Nikko Blue" since that seems to be the most commonly sold.
What zone is she in? If she lives near you it's much more likely that it's late frosts, in zones 5 and sometimes 6 if you don't protect them for the winter, all/most of the buds on hydrangeas that bloom on old wood (Nikko Blue would fall in this category) will get frozen off pretty much every year and you'll never see blooms. She needs to either protect them, or replace them with cultivars like 'Endless Summer' that bloom on new as well as old wood, then it doesn't matter what happens to the buds over the winter. The white ones are likely a different species like H. paniculata or H. arborescens which are more cold hardy and bloom on new wood so they'll do fine in colder climates.
She is in the same zone as me, so I had a guess that it was frosts getting to them. I'm thinking of adding some hydrangeas, and I wanted to find out what the cause of my aunt's complaint was before I had the same problems!
If you want the least amount of trouble/maintenance, I would go for the reblooming H. macrophyllas (like 'Endless Summer'), or H. paniculata or H. arborescens since those will all bloom on new wood. The others bloom on old wood and you'll have to be careful about protecting them every winter so they're probably not worth the effort unless there's one that you just absolutely love.
I just like the look of hydrangea in general - those big mops of flower!
I'll definitely look for "Endless Summer" - I'm a bit of a lazy gardner, and prefer things that can take care of themselves with minimal effort on my part. :)