After the flush of blooms... I have found the vigor of current seasons growth much improved... Neve fertilizer them if the soil is bone dry.... keep the ph right, the more acidic the better... add composted evergreen clippings..tea and coffee grinds too.
Watered soils here may become too acidic, in fact as long ago as the mid-1970's the Seattle Rhododendron Society newsletter was suggesting winter applications of dolomitic limestone. Heath family shrubs have an optimum pH range same as others and it is quite possible to make soil too acidic even for them.
Adequate drainage is vital for minimizing an increase in acid levels... ie clay soils would hold more water /less percolation and ultimately acid build up.
My 2 cents: I fertilize my rhodos now - putting it round the drip lines. Doing that and deadheading after they've finished flowering really makes a difference to both the quantity and size of blooms. Newbee