JanB wrote:
I have 2 Clethra plants that I purchased and planted about 10 years
ago. (at least) The local nursery from which i bought them suggested
these shrubs for my shady, acidic site in zone 5. One should have
white blooms and the other should have pink blooms. They have grown in
size and are nice and full but have NEVER bloomed. They are planted in
an area that is not wet, but also not too dry. Does anybody have any
ideas for me? I am considering replacing them with a different shrub
but if they bloomed, they would be perfect.
Thanks in advance.

Try cutting it back before you give up on it. Flowering occurs on the
new growth of the curren season. It's too late for this season but try
it for next year. This shrub does OK in most any condition. Best
performance occurs in partial sun to partial shade in moist to wet
acidic, fertile, organic soils.
HTH