Keep all mulch material away from the stem of the plant. The bark is easily rotted by the added moisture retained in the mulch. During the winter months, some mulch against the stem is suggested as being helpful in reducing winter injury to the crown of the plant. A soil pH of 5.0 to 6.0, in conjunction with small amounts of fertilizer, will maintain quality in most rhododendron and azaleas. Applications of sulfur according to soil test results will keep the soil pH at the proper level.
Fertilizers containing ammonium nitrogen seem to be best for the plants.
Don't apply too much nitrogen which stimulates excess stem growth. Once the nutrient levels are established in the soil, periodic applications of soluble fertilizer will keep the plants healthy. Fertilizer should not be applied after July 1 to avoid stimulation of additional tender growth that may not harden and mature before the winter months. Water the area well after any fertilizer is applied. As soon as the plants have flowered each season, cut out several of the longest stems.