I trust that it is planted in the ground. (not in a pot)
Hydrangeas will never thrive in a pot.
It looks as if it needs a good feed eg tomato fertilizer will help with flowering and getting healthier green leaves.( use as per directed on the bottle)
When newly planted or young make sure that you water it. ..not just a tiny splash. At least a couple of gallons every evening, especially if it has been hot and dry.
Add a deep mulch, eg leaf mould, well-rotted manure, or compost, in the area around it. This helps to keep the moisture at the roots and keeps the weeds down.
Hope this helps.
