I have a Rhododendron that we planted on the Northwest side of our house, under this overhang so the shrub doesn't get Michigan hot sun. My problem is that it blooms 2-3 flowers but that is it. The shrub is pretty woody and won't fill in. The leaves look good and the blooms are nice and full. Our dirt is nice and acidic but I just can't get it to fill in and bloom more than a couple flowers in the year. We planted this about 3 yrs ago. What can I do to make it look better?