Answer: Hydrangeas grow best in morning sun and with protection from hot afternoon sun. I think there may be another reason for non-blooming in your hydrangea, though. If the hydrangea came from the florist's it is probably a big-leaf hydrangea (hydrangea macrophylla). If so, it may never bloom for you again. Hydrangea macrophylla produces flowering stems on old growth. If your plant freezes down to ground level each winter there will be no old wood from which new flowering shoots can grow. As a result you'll have a beautiful lush, green hydrangea but it will never flower.
I'd give it a chance to perform, though. Wait until this fall and then move it to a site with morning sun.
Best wishes with your hydrangea.
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