How to germinate Rhododendron  seeds:

Rub peat moss through a 4mm screen to create fine lump free milled peat moss. Add 20/30 filter sand (10% content max) and greensand at 1 tbsp/gallon of medium). Moisten, blend well and fill pots/flats/WHT, tamp firm. Sprinkle seeds thinly on medium surface. Mist well. Give gentle warmth (20-25C). Lightly mist daily. Provide strong indirect light. Clear plastic cover helps maintain humidity and enhance germination /seedling survival by not letting medium desiccate. Seeds should germinate in 10 days. Never let seedlings nor medium dry out nor over water.  Prick out when large enough to handle into individual pots and grow on. Shallow rooted. Be warned seedlings have very fine hair like roots and can damage easily. Have pots ready to receive when transplanting to avoid roots from drying out