Hello, Caroline F. Well, your location and a picture of the leaves might help understand this "burned look". But if you have not over-fertilized, over-watered or added too many acidifying amendments, I guess that it still experienced soil moisture issues, made worse by windy hot weather, high summer temperatures and transplant shock in its first summer.

If you notice leaves browning from the edges inwards or the blooms browning under your conditions, it needs more water. A short 1-day dry event could simply dry out a few of the leaves but longer ones can trigger the root ball to repel water instead of absorb water. I have seen it happen with potted hydrangeas in Walmart Stores that they place by the main entrance instead of in the gardening section; these plants get some but not enough water and further dehydrate by the door opening and closing all the time.

To rehydrate a root ball, dumping the plant on water for an hour or keep it underwater it 15-30 after it stops sending little air bubbles. Then snip off the completely dry leaves, keep feeding it as usual and let it create some new leaves in several weeks (2-4?).

I try to water my potted plants by watering until I can see the water coming out the bottom of the pot, then I pause (maybe water another plant) and then water the first one again. A useful sign of water issues for me is when the soil starts separating from the sides of the pot or some leaves yellow out or brown out. I even recently got a soil moisture monitor to monitor excessive water in the soil from El Nin~o rains in my area; that was an useful tool to have... I am not implying these signs/tools always occur when the soil goes dry but they are useful tricks/tools that may raise a
yellow flag to more closely and more often monitor the shrub.

Was your plant a small gift, greenhouse, or florist hydrangea? If so, the foliage grown indoors isn't suited to any outside conditions. In that event, you must wait for the indoor leaves to shrivel and fall and be replaced by foliage adapted to the conditions.