I think I'll pass on 'Blue Bunny'. Don't want any bunnies in my garden, blue or otherwise. :Q))
Here's the one I'm waiting to try, 'Yohraku'. It is a normal sized involucrata, 6-10'H x 6-8'W at maturity.
I have been somewhat reluctant to try the species, since the initial hardiness ratings were Zone 8+, but I now note that they are hardy to Zone 5a, according to some purveyors?
Do you suppose there is some gene-splicing taking place somewhere? Maybe grafting onto hardy roots?
'Yohraku' is rated hardy to Zone 7, by this grower.
Rb

Here is a link that might be useful: Hydrangea involucrata 'Yohraku'

Rb, thanks.
Very interesting site and undisputedly very interesting-distinct 'Yohraku'.
Do you happen to know who will be selling their plants in US?
I'm in particular will be interested to try "Mikawa Chidori".

Here is a link that might be useful: Hydrangea macrophylla

George__
It's interesting to note that PoPP refers to 'Mikawa Chidori' as a macrophylla, while in Japan it is known as a serrata.
Peruse the link below (and drool :Q))). Also click on the links at the bottom of the page for a look at some of the phenotypes found in wild populations. A vast number of those have been named, propagated and sold in Japan. With the renewed interest in Hydrangeas here, maybe more of them will become available (Am I being too optimistic?)

Without some commercial growers in the US, I don't understand how PoPP can continue to introduce new plants that would only have a very limited demand in Canada due to clomate.
I emailed them. requesting a list of Eastern US growers.
There are 2 Wholesale Hydrangea producers in my area, but neither has any of PoPP intros.
Rb

Here is a link that might be useful: Hydrangeas in Japan

"Gene splicing" may not be far from the truth, RB :-)) Apparently crossing involucrata and arborescens to gain increased hardiness is already in the works.

Here is a link that might be useful: involucrata - arborescens hybrids

Well, seems like we shouldn't put a much faith in a 'gene splicing'. At least for now.
I e-mailed Sandy Reed and ask what happened to those remaining 8 plants since research abstract was published in 2005.

Here is her reply,
'The plants have flowered, but the flowers are white to very pale lavender in color. The plants are not fertile, so we have not been able to use them in further hybridizations  so this project is more or less at a dead end.
Hopefully, one day someone will find some H. involucrata plants with a little more cold-hardiness.'

I certainly hope so too.

Wonder if they will continue their breeding program, trying crosses with other hardy species? Haven't heard of anyone else doing anything with involucrata. Doubt if Dirr has anything going, as the last time I was at the CANR location (2007), they were still concentrating on macrophylla.
He has expressed an interest in developing a pink-flowered arborescens, using 'Annabelle' and a pink-flowered radiata, but as far as I know, nothing has progressed.

I guess PoPP has no licensed Hydrangea growers in the US, as I received no response from them. I used our Company name, which is a verifiable Dept. of Ag. licensed and inspected nursery and still, no response.
Rb