The more popular white mopheads are Emile Mouiller, Sister Theresa, Blushing Bride, and White Out. The first 2 bloom on old wood, however I have had Sister Theresa for 5 years, and cut it down about a foot above the ground every year and I still get blooms.... Unlike another old wood hydrangea that I did that ONE time to... never again, because it did not bloom the following year. So in my experience Sister Theresa also blooms on new wood.

The last 2 (Blushing Bride and White Out) do bloom on new wood, except Blushing Bride starts out white and blushes pink or blue. White out would be your best bet.... except it only gets 2'x2' :(

The more I think about your post, I think Sister Theresa would be perfect:

1. blooms on new wood (In my experience it does)
2. can handle some sun - will get a little shade in pm (My sister theresa was in full sun---afternoon sun even and did fine. She'd get a bit wilty at times, but would recover by evening. Morning sun would be absolutely perfect for her.
3. 5 feet tall (Yep)
4. requires no staking (Nope)
5. pure white (or as pure as it can be) (see attached pic)
6. long growing season (It's the end of July and mine is still going strong)

Here is a Sister Theresa I bought back in early June because it was SUCH a beautiful plant. I am waiting to move a tree in the fall and will replace it with the ST. Until then she has sat in the pot on my front porch in morning sun---and seems to love the spot.
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The only thing about Sister Theresa---is that her blooms are so large, that they don't seem to do well as cut flowers. I can never get them to look nice in a vase the way the other rounder mopheads do. So if you're planting soley for landscape beauty (and wouldn't dream of clipping off the blooms) then IMO I think she would be a great choice for you!

sister theresa is gorgeous. it will be just a landscaping plant - not planning on cutting off the blooms. thanks so much for all your help!!!

All I can say is WOW!! That is some gorgeous plant!! Sister Theresa is definitely on my wish list for next year!! Beautiful photos, they say a picture is worth a thousand words and so it is!!

Donna

zone 9 I would try BB-it does rebloom and for me ST blooms but once-though beautifully...

thanks everybody for your help! i sure am glad i found you guys.

i love BLushing Bride
on mhy wish list

My annabelle and (I don't have the other name of the white mop head) once they bloom white they turn green. Sometimes they just bloom green, beyond ugly.

What am I doing wrong? I live in a state where the state flower is the Oakleaf Hydrangea, so they're everywhere.

Even my pretty pink ones are turning green. I use to grow hydrangea's in all colors when I lived in town, except white.
Should I fertilize them? I did use a cup or two of perlite in my top soil along with peat moss and egg shells.

Incidently the white ones above are simply gorgeous.

Oh the weather here in Alabama has been in the high ninty's and over 100 for six to seven weeks or more. But I have mine in semi shade.

I use to be a pretty good gardner now I stink.