Rhododendrons aren't among shrubs that can be 'shocked' into blooming by pruning; the purpose of the mulch is to conserve water and cool the roots.

You don't say how much shade your shrubs are getting...they need some sunlight to set buds and bloom. Also, drought during late summer when they are setting their buds for the following spring can lead to lack of bud set....Is the shrub next to the walkway close to the house staying more dry than the other?

I agree with Morz8. Either shade to summer dryness is probably your problem. The flower buds are forming in late spring and early to mid summer. If they are dry then they will conserve moisture and forgo setting flower buds. They need at least 2 hours of sun during this period to set buds. A minimum of 2 to 4 hours of sun on a typical day is the typical recommendation.

It sounds like summer dryness, since they get plenty of sun. The one that isn't blooming is a bit taller than the blooming one, so might need more water than it's partner does. Have to get some more soaker hoses for my garden and add some mulch! Thanks for the tips! Here's hoping next year I see some blooms again!