Answer: I wonder if the affected flowers, those exposed, are actually turning brown or developing brown spots because of overhead watering? When droplets remain on flower petals in hot sunshine, they can become little magnifying glasses and actually burn the tissue of the petals. This would explain why the flowers near the center of the plant are unaffected. Just a thought.
You can safely move your hydrangea this winter while it is dormant, or early in the spring, just as new growth begins. Start by digging the new hole, then pruning your hydrangea back so it's a more manageable size. Carefully unearth the plant, trying not to sever too many roots. Place the rootmass in the new hole, making sure it will rest at the same soil level as it was growing before. Backfill and gently tamp the earth around the roots, then water well to help settle the soil. Your hydrangea probably won't even notice it has been moved.
Best wishes with your landscape!
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