Bonsai-care - Fertilizing
A basic rule is to start fertilizing in spring when the tree becomes active. Liquid fertilizer is then used every two weeks until autumn. Organic fertilizer (Biogold) is spread on the surface of the ground (one piece per centimeter potsize) and lasts nearly 2 months. Repeat except during your hottest month. Afterward continue until autumn. Do not fertilize outdoor bonsai in winter, indoor bonsai with liquid fertilizer only once a month.
Never use fertilizer in the first month after repotting to avoid probable damages of the root system.
Fertilizers mainly consist of nitrogen, phosphorus and potassium (N-P-K). For bonsai balanced fertilizers with a strength between 4 and 8 are suitable (e.g. Biogold N-P-K = 6-6-5). If you are eager to manage bonsai-fertilzitation perfectly refer to the following table (please start fertilizing rhododendron only after flowering):