Fall Season Care for Rhododendrons
Reprinted from the Mason Dixon Chapter newsletter, September 2008.
Mulches which maintain a more consistent soil temperature and moisture level are typically associated with the native habitat of rhododendrons and azaleas. The same benefits can be derived from a mulch when used in the landscape. A loose, coarse mulch extending beyond the root system is of great vale in the landscape and helps prevent many problems. By virtue of shading the soil (thus lowering soil temperature), the mulch greatly reduces moisture loss. The soil moisture level is maintained at a more consistent level, which leads to uninterrupted root development. Since water loss is reduced, the need for irrigation is also reduced.
The soil organisms producing root rot in rhododendrons and azaleas require both high soil temperatures and wet soils to become infectious. The cooling benefits provided by mulch can act as a disease prevention measure.
Organic mulches also provide plant nutrients as they decompose, helping to maintain soil organic matter levels. Proper mulching is a must throughout the life of the plant and is second in importance to proper watering, the number one maintenance practice.
Apply new mulch each year late in the fall or early winter after the plants have hardened off and rodents have found other winter homes. Only coarse materials such as wood chips, shredded bark, leaves of most deciduous tree species, or pine needles should be used since they allow better oxygen exchange between the roots and the air. Maple leaves, grass clippings, or peat moss are not good mulching materials as they can pack down too tightly. Very coarse materials, such as oak leaves and pine needles can be applied 3 inches deep. Finer materials, such as ground pine bark ¼ inch in diameter, are applied only 1 inch deep since oxygen does not pass through them as readily. Keep mulch a few inches away from the main stem of the plant to avoid an environment conducive to crown rot. Since there are no feeder roots this close to the plant stem, any drying out of the soil in this area is of little consequence. Mulches are often applied too deeply in the landscape, which leads to severe root damage and death for any number of plants, including rhododendrons and azaleas.