How to Fertilize Rhododendron macrophyllum?
Diluted rhododendron feed twice yearly spring and early autumn

Rhododendron macrophyllum · Rhododendron macrophyllum
Grow in moist but well-drained, humus rich, acidic soil, in partial or dappled shade. Choose a site away from frost pockets and sheltered from strong winds, and do not allow plants to dry out. Mulch annually, ideally with leaf mould. See rhododendron cultivation for more detailed advice
Diluted rhododendron feed twice yearly spring and early autumn