Hi,
I'm not far from you, and I have a PeeGee in tree form near my pond. I suppose it could be happy in a pot (though I wouldn't recommend it). It would take a pretty huge pot. Also it would require ample watering and nutrients in the form of fertilizer to sustain it as it matures. My mother and I both have bush varieties potted that are not hardy in Z 5, and we bought the largest retail pots we could find, overwinter them in the garage. They reward us with beautiful blooms that otherwise wouldn't be there if our harsh winters had gotten to them. But two of the larger varieties aren't so happy as they age, probably need more root room/wider pots (like those large pots you see tropicals in that are inside a mall or one of the commercial/medical office buildings downtown.) Their outer branches aren't upright as they mature, they tend to want to curl, swirl and floop, so I have to use plant hoops to stake the branches up.

Honestly, you'd be surprised at how you can fit a tree form into your landscaping. I got my PeeGee tree form after I saw one at a local yard sale, the man was cutting flower heads for drying and gave me a bunch. He had his in a corner of his privacy fence, it was spaced probably 2' from the fence. Blooms billowed over the outer corners of the fence, just gorgeous from the street. So I went and bought one (a Charlie Brown that needed TLC for $5). Mine is also in a corner of my privacy fence, directly behind my pond. It's planted about 2 1/2 feet from the fence. It's about 6 1/2' high and 6' wide at it's widest at the top (spreading 3' from the trunk in any given direction). Mine is about 8 years old, I prune it every year to shape it and train the growth upward instead of outward. They can be maintained to a manageable size. The man whose PeeGee tree I so admired said his was quite old and he just cut it back every year to about 8' tall by 4' wide or so each spring at bud break. Either way, potted or in the ground, be sure to use an ample layer of mulch to keep the soil moist and cool. When I potted mine I used a generous amount of water crystals in the soil to help maintain the moisture level during hot spells.

I think I might have misinterpreted your question. When you said "hydrangea tree, I thought you were referring to the PeeGee variety, which is often trained as a tree. (You can buy it from nurseries already started as a tree form.) You can read up on PeeGee and see a few photos here.

If you were referring to potting any type hydrangea, be it PeeGee 'tree' form or any 'bush' form, then the answer to your initial question in general is "yes". PeeGee is tough and will withstand our winters and bloom just fine. But other varieties, it's touch and go depending on our weather. So that's why I pot my more unusual or delicate varieties, so they have protection in the garage. I find Target has nice decorative plastic pots that aren't terribly expensive.

I have Nikko in the ground as well as All Summer Beauty, Domotoi and Endless Summer. It's hit or miss whether I get a good bloom show, our winter can be hard on them. This winter was Endless Summer & Domotoi's first winter in my flowerbed. ES is loaded with blooms, but Domotoi isn't showing any yet. It's a later bloomer, but still, I think it might have to be potted, just too darn cold here for it.

I just went out & took some pics for you. Here's 3 of my potted ones. On the deck is a "Pia" (a dwarf variety, hardy in our zone but I wanted it potted for the deck). In the gray pot on the right is "Masja" (a beauty and full of buds this year!) and in the largest pot in the back is "Ayesha". That's the one with the drastic curly-q outer limbs. Some of my "in the ground" hyds also get curly-q on the outer stems, but not as drastic. Ayesha is already in a whopping big pot, but still would do better in a bit larger one. I forget how many gallons the Ayesha's pot is, but it's the largest size you can find at most retailers.

Here's my PeeGee tree form, by the pond. Looks a little sparse right now, it's just beginning to leaf out. As you can see, it takes up minimal ground space, it's the upper branches that need space. One of the mistakes they made with it (and why it was probably reduced to $5) is they didn't prune to get the "V" high enough off the ground. I'm trying to train it to a better shape, which takes a long time. So if you decide to buy a PeeGee tree form, look for one that has has a longer trunk for balance when it matures (I'd suggest 4' from ground level, minimum).

I use good potting soil (I like Fertilome's "Ultimate" potting mix, it's supposed to be a good mix for container planting). I use water crystals in the soil at planting time. Then I add a good 2" layer of mulch to the tops of the pots. I find I have to drench them regularly in the heat. I feed them with Schultz Bloom Plus for Acid Loving plants because I prefer bluer blooms. I also keep them under a tree where they get dappled sunlight. I bring them into the garage around late October (I don't let a hard frost get them). In winter I water maybe once every 10-14 days, no fertilizer since they're sleeping. And I bring them out of the garage in late April/early May. I wait till the trees have leafed out so the canopy it creates is added protection should we have a late spring frost.

I actually prefer the multi-trunk form, which has an heirloom look, like the incredible old tree hydrangeas that you see in Maine, or in some of the older plantings in Montclair, NJ, where I live. The interplay of the multiple trunks makes the line more complex and, to me, more charming.
At the same time, i might like a bit of a head start, and wonder -- do the "lumps" where the limbs have been clipped off (and which tend to be prominent in the nursery offereings) disappear as the tree grows larger?
Would also like to know what varieties has anyone had particular success with training into tree form?

Krissnyc, we have trained limelight, the swan, unique, and pink diamond, all paniculatas into tree form. The pink diamond actually seems to grow naturally that way. But I like the old fashioned shrub form better also. And speaking of shrub form, has anyone yet grown white dome, (Hyd. arborescens 'Dardom'). What a beauty for an old fashioned look.

Curious1...I wish I would of seen this post earlier. I live int he suburbs of Chicago. I have had my hydrangea tree in a large pot for over 5 years...It's int he sun protected by a wooden fence. It probably should be in a larger pot (maybe next year)...It is blooming, blooming & blooming. Never have had any trouble. Easy tree for small garden. We just move ours around!

I purchased a small hydrangea at a flower show in Chicago and potted it this summer for my deck. I have now brought it in my house for the winter and probably will put it down in my very old basement that has little heat. This is a first time experience so I am looking for any ideas and help to have this plant survive the winter so I can put it back outside in the spring after the final frost.

emoleson Oshkosh, WI

The suggestions for containerizing hydrangeas in colder climates from Hinkley (Heronswood) are -
A gallon sized plant should be moved directly into a 15 - 25 gal container using a bark-based soilless potting medium.
Move containers onto an unheated porch, garage or greenhouse during the winter season, protecting only during the coldest temperatures.
Fertlize and water as for those plants grown in the ground.
Replace growing medium every three years.