I would leave them where they are and fertilize them this fall & put some epsom salt (sprinkle 3 or 4 tablespoons around each). The only other things are water and don't trim until after they bloom as some bloom on old growth and some on new growth each year. Lots of water and mulch with pine straw or oak leaves ground up with the lawn mower.
It kind of depends what zone you are in and what type of hydrangea you have whether they bloom. Many times if you don't have a hardy hydrangea that blooms on both old and new wood, the blossoms fall off with a frost and then you don't get any flowers. The hydrangeas that bloom on both old and new wood are your best bet if you want flowers. I am in zone 5 and the hydrangeas that are suited for the south are not suitable here.
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