Rhododendron is a large genus of perennial flowering shrubs or small trees of which most species are evergreen. They are grown for their lush spring and early summer blooms and their distinctive bronze green foliage in the fall and winter. Rhododendrons are grown as specimen plants in the garden and massed to create hedges, wind breaks and visual screens. Rhododendrons are acid-loving plants that require a soil pH between 5.0 and 5.5. A combination of good soil culture and feeding with an acid-rich fertilizer will keep them performing optimally.
Mulch around your rhododendrons at least once a year with a good quality compost to boost the nutrient value of the soil. Lay down a 2- to 3-inch thick blanket starting 4 inches out from the central trunk to 8 to 10 inch past the drip line of the shrub. Replenish the compost as needed.
Fertilize your rhododendrons once or twice per year with an acid-rich formulation such as MirAcid or another commercial formula designed for use on rhododendrons, camellias or azaleas. Use the manufacturer's label instructions to determine dose, but do not exceed the application rate of two pounds for every hundred square feet. Always err on the side of less fertilizer, as more can cause root burn or disrupt bloom.
Water in the fertilizer well at every application to reduce the chance of root burn or stress. Water deeply at the roots from the trunk to the drip line for several minutes to saturate the soil, and allow the fertilizer to begin percolating down into the soil.