Why is my Rhododendron not growing after being planted in my garden ?
Certified GKH Gardening Expert
That will be very hard to say with no details about the planting, pictures of the plant, or details about the area that you live in.
I can take a few guesses, though.
This can be attributed to a few things- Lack of fertilizer in the soil can cause slow growth, as can over and underwatering. Disease can stop growth, as well as insect damage.
What I can do for now is put an article, here, that will help you to know what they require for care: https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/rhododendron-care.htm