Northern exposure is rough on rhodos. Drying winter wind dries out the foliage unless there is some sort of windbreak. Rhododendron can take morning sun until about noon so the east-facing wall is best…that way the house will provide shelter form winter winds that blows from the north and west. Rhodos set their buds the summer before and those buds wait until spring to open. If winter wind dries out the buds too much, they just dry up and fall off in the spring without opening. Yes, poke some holes out away from the trunk of the rhodos and pour some Holly-Tone evergreen food into the holes right away. See the package for the correct amount to use. They need the food now and you could fee again in 8 weeks, this should be done every spring. Check to make sure you haven’t piled mulch up against the bark of the stems of the plant where they come out of the soil this smothers the crown of the plant and makes it hard for moisture and nutrients to move through the bark to the stems and leaves. It may take them a couple of years to regain the extra vigor they need to produce flowers. If they form flower buds this summer, then you can expect flower in spring…perhaps building some windbreak of burlap will help them endure the northern exposure. If they are getting less than 4 hours of direct sun a day in summer than they will have trouble flowering.