Shrub for site under a silver birch

CatWoman23

Hi, I recently had my garden landscaped but a m doing all the planting myself.

i have a large border under the shade/ dappled shade of a well established silver birch. I'm looking to fill quite a lot of space!

i had an idea that I could maybe plant a rhododendron with big beautiful flowers as my main feature. Is that good idea for the position? or is there anything else that's suitable? 

Thanks! 

Forester2

I have ferns, hardy geraniums and cyclamen under my birch. Not sure about rhododendrons as my soil isn't suitable for them,  I also have an oak leaved hydrangea very close to it in dappled shade.