All hydrangeas are woodland understory shrubs who prefer shade in the afternoon. Amongst the most sun tolerant ones are quercifolias and paniculatas, which tend to be large unless you choose some dwarf versions like Sikes Dwarf, Little Lime, Ruby Slippers, Pee Wee; or you can grow larger ones and prune them every now and then to keep their size in check. Since you do not live in a hot climate, I would try a quercifolia (aka, oakleaf) or a paniculata); if you notice that the leaves in direct contact with the sun are getting sunscorched during the worst of the summer, transplant it to another location.
If you want to test the waters, you could always get a hydrangea and place it in this area pot and all. Just dig a hole & put the pot and plant both in the hole. Cover the sides with soil and put mulch on top (3-4"). Then monitor the leaves often during the summer. If the leaves are not affected by the start of the Fall, take it out of the pot and "formally" plant it in that same spot.
I'm in zone 7, with intense summer heat and humidity. I have a Limelight hydrangea that gets afternoon sun from about noon to sunset. It's probably the healthiest plant I have in my yard. In fact, paniculatas reportedly don't bloom as well in the shade.
A dwarf version of Limelight is Little Lime, but you should be able to prune Limelight to 4-5 feet. I pruned it hard in February (flowers on new woods) and it's leafing out beautifully.
In the summer, the leaves get sunscorch here and HAVE to be protected. Kind of catch 22 balancing act, hu? You get more/better blooms with more sun but you keep the green lime color longer with more shade. Makes you want to have some kind of lever to twist and control sunlight amounts that way. Hee hee hee.
Hello, pirl! You know, I have always wondered how well white hydrangea blooms would do in a moon garden. The paniculatas that stay white-ish longer would be better choices for that I think. Or maybe one should use white macrophyllas. Hmmm.
You're right, Luis. Gardens need giant umbrellas that protect the vulnerable plants while allowing the sun lovers total access.
I'd guess the choice of which white hydrangea to use would be based on proven performance in your area. You know I love my Tardiva and it is slow to go to the pink stage but White Dome is nice and there's always Annabelle but I don't like her floppy heads.
A California friend, now getting ready for this weekend's big Mary Lou Heard Memorial Garden Tour, removed the fabric from two typical umbrellas and replaced the fabric with shade cloth to prevent burning. Naturally, he's had damp weather since he did it! Much of gardening seems to be that delicate balancing act.