Mophead hydrangeas are hardy to much colder zones without caging. And my oakleaf and climbing ones do fine with no protection.

If I were you, I would remove the caging. Sometimes, mopheads take a couple of years to bloom once they are set outside.

The average last frost date here in Middle TN is April 15.

The older varieties like the popular 'Nikko Blue' do bloom on old wood, so you're wise to try to protect those branches. You should be able to uncage the plants now though. A frost won't kill the wood/buds; a long hard freeze does the damage.

Newer varieties like 'Endless Summer', 'Dooley' and 'Penny Mac' bloom on new and old wood, so they bloom even if all the above-ground structure of the plant gets killed over the winter.

Marty

Speaking of blooming on old wood...the year before last I cut my 'Nikko Blue' and a few other Hydrangeas that supposedly bloom only on old wood down to 1" above ground level. I did this partly because I was working in the beds and wanted them less in the way. They had almost as many blooms that spring as when they had not been cut. My experience has been that all Hydrangeas I have tried will bloom (at least to some degree) on new wood. Anyone have different or similar experiences?

I can't say from my own observation (since I've never tested it for myself) whether 'Nikko Blue' blooms 100% exclusively on old wood. All the books say it does, though. Perhaps when you pruned you left a viable bud below the cut. It would bloom from that. In fact, it's those lowdown, near-the-ground buds on the old wood that produce most of the bloom in my experience, not the ones up higher, even though they sprout and grow nice leaves.

And then, books are often wrong, though, too. :)

Marty

I cut the whole thing to the ground. It sprouted to about 4' high and there were blooms all the way to the top. Like I said, maybe fewer blooms, but definitely enough to still be pretty. I had 3 other varieties that I know at least two are "old wood bloomers" that did the same thing.

I'm new to TN and just now getting around my new yard. I love hydrangeas - had some lovely ones in Maryland. Do they do well in the Memphis area?

They should do great in partial shade with good soil. They may not be at their prime if you plant them in full sun. If you don't have shade, I would at least go for an area where the evening sun is blocked (eastern side of house).

I have several different types of Hydrangeas, and never
do anything to mine, but cut back a bit,when they get to
big. I fertilize them monthly with Miracle Grow Bloom Booster. They seem very happy. I generally water the entire garden every morning, especially when really hot. My favorite Hydrangea currently is Madame Emille Molliere.
It blooms White and after a few days begans to turn the softest pink. I also have Ravel,which is Pink with a White
center. My Oakleafs are 6 foot tall and covered with buds.
I can hardly wait until they bloom. Oakleafs are just the most beautiful Native Shrub we have I think.