Hydrangea seemannii x petiolaris Semiola is a new plant I have bought and potted up against a wall with no sun. The leaves are going
brown and dropping in the middle. I have kept it watered in the drought. The top and bottom have new shoots. I have fed it weekly.
Certified GKH Gardening Expert
I would back off the fertilizer every week. They do need fertile, well-drained soil, with about 1 inch of water a week. If your soil needs improvement, you can topdress with compost now if you didn't work some in before planting. They need high phosphorus fertilizer in the early spring before leaf bud and again in the summer after flowering.
Also be sure when you water you are not watering the leaves. Keep the water on the ground. Water on leaves can lead to fungal issues. Just a side note, they will grow and bloom in full shade, but will bloom more if they get a bit of sun.