Rhododendron seeds, small and delicate as they may appear, require scarification to break through the tough seed coat, as this allows moisture in to enter the seed and begin the germination process. Since the seed is often quite small, this must be done using the following technique:
First, take a 15cm (6in) clay pot, that has been washed and sterilized, and fill with sterilized seed starting mix. Firm the mixture in the pot and level it of about 2cm (1in) below the rim. Take a small amount of damp sterilized sand, just enough to comfortably fit inside your fist, and mix the Rhododendron seeds into it. Rub or crush the mixture between your hands once or twice - please do this over a large plate or other container to catch any that falls out.
The mixture may then be spread on the surface of your carefully packed starter pot. Dust the surface lightly with dry peat moss and water in gently. Please note that the first watering is from the top to help the seeds settle in, but any subsequent watering should be done by placing the pot in water that comes within 4cm (2in) of the rim for a minute or so, or by placing the pot on a capillary mat (recommended).
Germinate at 15ºC (60ºF) and grow on in a well ventilated but sheltered location in bright light, away from any direct sunlight.