Paniculata Grandiflora, "PG", is certainly tried and true. I've seen huge monsters in my part of the country and pictures here on this forum. It might take a long time to get as big as the one you want.

I've seen Kyushu that are eight feet tall and they've been planted for at least 5 or 10 years. I don't know if they'll get bigger. Tardiva the same way. Are these naturally smaller or they just haven't been in the ground long enough? I don't know. Their habit seems to be different to my eye. More branching and less tree like. Interesting question about how big they might become.

Dirr in his Manual of Woody Landscape Plants says, "Paniculatas are 15 to 25 feet in height, quite variable in size, often 10 feet or less. Rate: fast. Praecox will grow between 10 and 15 feet in height. PG was introduced from Japan in 1862. "

Good luck. Hay.

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WOW!!! That's one heck of a PeeGee!!!!!......yg

holy cow...is that Pee Gee tree truly in your zone 5/6? I wonder how old it is.

30 years old PG could attain enormous proportions, something like this (20'x 20')
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but could be kept at any desired size as it's prunable.
Lately I had a chance to inspect (closely) several of 10-15'+ PGs growing at old cemetery and all of them had one thing in common: thick scraggy unbranched trunk to 4-5' and then thinner, but still not productive branches that start producing live shoots only at 6-7' height off the ground. Due to droopy nature of PG, everything above 3-4' was green and flowering (from the distance), but I'm affraid that in a winter and spring it will be not a sight to admire.
So, my point is, that since you'll be looking at your tree not from a long distance, but rather closely, you might be better off to grow it as a shrub rather than a tree.

Just in case you'd like to see a 'Kuyshu', here it is trained to a tree. It's about 5-6 years old (2 years in my garden and another 3-4 years were trained to tree form by grower) and about 7' tall. As you could see it's much more upright than PG.

I think most of 'full size' paniculatas could reach your desired size, but when choosing among them I'd avoid Tardiva as it is a latest to leaf out and bloom of all of them and in your zone you'll not see flowers probably till end of August, while Kuyshu start blooming in late July.

Thanks for the stunning pictures. What are the difference between Pee Gee and Kuyshu? Will Kuyshu continue it's more upright tendancy even when larger? Blooming in July would be fantastic. I was led to looking at Hydrangea Paniculatas in a quest to find a summer flowering tree. I'd be excited with July & August blooms. Ideally I'd like to be able to prune it so I could walk under it.

Are the Kuyshus readily available?

Thanks for all your help!

This year I planted a Pink Diamond, tree form. It looks similiar to EGO45's Kuyushu except the panicles are looser in their appearance. Less flowers on the panicles. Bloom time was late July and now it has turned a nice pink colour. Very Graceful looking. I have a Pee-Gee tree form and it has a weeping habit and more vigorous growth. I cut the branches back hard. Overall I like the more open airy look of the Pink Diamond.
They are readily available here in Ontario and you may find them on sale!

Good luck,
Sue

eks, there are 2 main differences between PG and Kuyshu,
1. Flowers. PG flowers consist mostly of sterile florets and look like a mophead hydrangea except that form of the flower head is not a ball, but panicle, hence the name, Paniculata. Kuyshu flowers consist of combination of fertile and sterile florets and has more airy (see-thru) appearance.
2. Habit. PG is weeping/drooping due to the heavy weight of the flowers that can't be supported by new thin branches on a tips of which flowers appear. Kuyshu is much more upright plant due to the fact that flowers weight less and stems could hold them without bending down.
Here is PG for comparison.

Until few years ago, PG and Tardiva were the only cultivars readily available (at least where I'm). Since Kuyshu made it entry into market, it's become clear that Tardiva is inferior to it and now you could find Kuyshu even at a big box stores.

Has anyone had experience with the hydrangea tree variety called "unique"? How would you compare them to pee gee in terms of hardiness, blooms, color, etc.? thanks.