North side is totally wrong. While they can take shade, they still need sunlight.New Yprk still sets about the same latitude as WA and the lower angle of the sun for most of the year makes it like partial shade. They love acid soil too so top dress with peat or pine straw.

Have these rhododendrons been in place for some time then, and not something newly planted? Your problem may just be lack of summer water. I have drip hoses in all my perennial shrub beds, even in the damp pacific northwest where I use them only about three months of the year. Lack of summer water can be a reason for failure to flower the following spring.

Shade is another reason, and while they can take almost full sun here in my maritime location, my rhododendron books state "a northern exposure is the safest location for rhododendrons and azaleas. There, sun rarely strikes the plants, yet, if the location is open to the north and not blocked by dense trees or another building, the amount of light received will be entirely satisfactory for good growth and performance."

I don't mean to be contradictory, but never top dress with peat. Once dry, irrigation will run off a peaty surface rather than penetrate and compound any watering issues. Partially decomposed organic matter makes the best top dressing/mulch....compost. If you don't have your own, buy it by the bag....Home Depot here has well aged, odorless steer manure mix for just $1 per bag. If you put a couple of inches over the root zones in Spring, reapply in Fall if needed to keep up a constant supply, you can come close to duplicating how most rhododendrons grow in the wild.

Sorry, I missed your question how often. That depends on your soil type, summer temps, wind. These are not drought tolerant shrubs and need regular water - test with a spade after watering and make sure any water you have applied has penetrated more than just a few inches, repeat when dry...With my clay amended and top dressed with compost, I run dip irrigation several hours to give a long slow soak every 7 - 10 days.

My house was built in the '20's and has a cement basement...watering near the foundation with the 'oozing' type soaker hoses has not caused any problems for me. I don't recommend letting an overhead sprinkler run for long periods of time, with that heavier spray hitting the house though :)

I've got a rhododendron in a similar situation - north-facing foundation bed, and mine was planted with part of it under the eavestrough. We've got plenty of trees on our property, and our front yard is pretty shady. Last spring, I was disappointed that my rhodo had no flower buds at all. We had to have a large tree taken down that was too close to the front of the house; and I'm very happy that it has opened up the front yard to more light. The rhodo is now getting more sunlight, and 'open' light, and the best news - it's full of flower buds this spring. So, I'm pretty sure is was not getting enough light.

I find it pretty convenient to keep the front foundation bed watered since it's so close to the hose - lol. I don't have soaker hoses (I may have to put some in after reading mor's post), but every now and then, I'll will take the garden hose and lay it on the ground at the base of the rhododendron. I let the water just trickle out for an hour or two. This gives it a good watering. Of course, I never let the foundation bed stay dry for too long, either.