A "tree hydrangea" reference is normally used to point to the H. paniculata known as Pee Gee Hydrangea. But its blooms are supposed to be white, never colored like blue or pink. They might appear a little green maybe at first but not I have never seen colored blue.

Blue hydrangeas are typilcal of a H. macrophylla.or serrata that is growing in acidic soil.

Thanks, the flowers look like the tiny center flowers of what I think are the lace cap type of H. macrophylla.

So I guess it will get around 6' tall (it's about 3' now), and I can plant it where I planned.

Will it possibly develop larger flowers (bracts?) later, or do you suppose it will always have just the tinys? (They're less than 1/2" each.) At least it has a LOT of flowers; that's almost as good as big flowers! (My ideal flower: large, ruffly, bright colored, and fragrant. Good thing I live in the tropics.)

BTW, we do have extremely acidic soil; the mostly white hydrangea in the photo above will be bright blue in a day or two.

A little bigger flowers yes and with time. But don't expect earth shattering different sizes. What I also would do to explore what happened is try to isolate where the plants came from and then contact the person or the nursery that supplied the hydrangea shrubs to see if you get more details and maybe a variety name. Once it gets larger, if it is compact, it may be a H. serrata, which usually has lacecap flowers.

And yes, I agree. The immature blooms start sometimes green, white or yellow and then turn blue/pink after almost a week... or so. Enjoy!

Toss-up on what exactly it will do in zone 12. Hydrangeas are deciduous plants (need seasonal changes), but certain kinds have been known to grow in the tropics.

Here is a lengthy discussion that occurred here on the subject:

http://forums.gardenweb.com/discussions/1991310/i-saw-hydrangeas-that-grow-in-the-tropics-know-any-names

If the cultivar was not named, there's no real guarantee it's any particular kind of hydrangea, but there are some things like H involucrata that have been known to bloom in this fashion. Looks like your garden club needs to do some homework. ;)

I'd suspect this is not a hydrangea at all but a more tropical climate relative, Dichroa, probably Dichroa febrifuga. This is native to Southeast Asia - so should grow well in HI - and is a large growing shrub (7-8') and semi- to nearly fully evergreen. The flowers differ in that they are tiny and with virtually NO production of any sterile florets like one would see with a bigleaf hydrangea. They are followed later in the season by bright blue fruit, giving rise to its common name of "blue bead plant".

It tends to be rather uncommon in this country as it has a much more limited hardiness range than most other hydrangeas or similar plants but grows well here in the PNW. There are a number of these at the gardens of Heronswood Nursery and poster ophoenix has one in her amazing north Seattle hydrangea garden.

Thank you all for your input. My plant's flowers do look like the Dichroa.

Hydrangeas (of some kind) do grow well here, keep their leaves year-round and bloom off and on all the time. They don't get huge, most of the ones I see are about 2'-3' tall. They do grow well even at low elevations, like 200' (I'm at 1500').

Here's one in my yard (bonus weedy vine included!)

In their defense, my garden club actually focuses on water plants. Like any small town, most plants here are passed around as cuttings and names get lost or garbled.

Even nurseries are not to be trusted; I got a hibiscus labelled "Pizza Hot" at one, expecting bright cheese-colored blooms. Instead it had pretty pale yellow flowers. I discovered that my variety is actually called "Rag Doll" and got the nickname "Pizza Hut" because it was discovered growing next to one of their stores. The nursery had further degraded the name by mislabeling. But it's still just as pretty! A rose by any other name...

Heck if I had a garden in HI I think it would be 95% hibiscus. The tropical kinds are sold as large expensive annuals here.

You would concentrate on Hibiscus until you discovered Vireyas. Tropical rhododendrons, 6' tall shrubs that bloom off and on all year in white, red, pink, coral, orange, yellow. Some are huge, some are fragrant, and some are even ruffly!

Then you'd realize you can hang orchids on your trees...

so many plants, so little time.