Q.Are Garages Too Dark To Overwinter Rhodedendrons
Just been given a rhododendron in a pot and want to be prepared for winter months living near Reading

Certified GKH Gardening Expert
Yes. These are evergreen, and will require growing conditions similar to summer. You are, actually, at the upper end of where they will survive. Winter protection will not be necessary, but if it gets warm in your area, you may need to plant it in deeper shade. They will not tolerate full sun, no matter what area you are in, though.
This article will help you with the care of these shrubs:
https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/rhododendron-care.htm