The Rhododendron should be fine in full sun. Most soil in this area is acid enough for rhodies, azaleas and camellias. The hydrangeas would benefit from some shade in the afternoon, and also a site protected from strong winds, because they tend to be delicate when in bloom. Is that four hours of sun the morning sun? If so, that should be fine.

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Hydrangeas thrive in part sun but do require acid soil in order to bloom but the most important thing they need is water. The 'hydra' part of the name says it all. So long as they have adequate moisture, they should be fine.

I have peonies growing beside hydrangeas in part sun but also have them growing in full sun. They thrive & bloom heavily in both locations which suggests they're happy in either. I've seen no indication of more stingy blooming in part sun. The key with peonies is planting them so the stems are growing at the same level as in the pot--plant them even slightly below that and you'll be wondering why your plants don't bloom.

My soil is naturally a bit acidic which pleases the hydrangeas. I dump wood ashes on the peonies in January or February each year because they prefer a more neutral soil Ph-wise.

Hydrangeas don't particularly care about pH. My soil is naturally alkaline, and aside from winterkill (zone) issues, hydrangeas are perfectly happy.

The rhododendrons do care, and if you lived in NW Conn, I'd strongly recommend a soil test. There are lime pockets around.

Your pH should be fine for Rhododendrons in NE CT. The Renegade Gardener is in the midwest, MN I think, where you do need add supplements to grow rhododendrons since the pH is more alkaline than they like. Rhododendrons do prefer relatively organic soil, so I usually mulch them with wood chips which will break down over time and supply organic matter.

My mophead hydrangeas are happier with morning sun and afternoon shade than with full sun. They tend to look a bit droopy when they are in full sun. That isn't true of Hydrangea paniculata, but the ordinary mophead H. macrophylla prefers some shade.

I find that here my rhododendrons bloom and grow fine in either sun or part shade, but in winter they end up with less damage to the foliage if they get some shade, so I tend to site my rhododendrons where they may have full or part sun in warm weather, but they get at least some shade (due to the lower sun angle) in winter.

My peonies bloom well in part sun or full sun, and they all seem to do just fine in the same acidic garden soil where the rhodies and hydrangeas are happy, so I don't think that they are super fussy about pH.

Thank you for all your responses! Planting will commence this weekend, in between a garden tour tomorrow. Can't wait.