The benefits of mulching are many. The first of these benefits is that mulching conserves moisture by physically holding it and releasing it slowly to the soil beneath. Since rhododendrons like a damp soil, this is an obvious plus. Mulch also conserves moisture by reducing evaporation by up to 90%. The result of this conservation is that the need for external water is reduced by one third to one half of that needed for un-mulched soil.

Mulches also moderate soil temperature. Mulched soil is up to 10°C (18°F) cooler on hot summer days and up to 10°C warmer during chilly spring and fall nights. The heaving of roots by frost can be prevented as can the drying of roots by high temperatures and winds. The shock from sudden changes in temperature can also be moderated by mulching.

Soil compaction and erosion from heavy rain, wind and hail can be prevented. Mulching can protect the plants from soil compaction due to foot and cart traffic, cold water on hot days and overdoses of water, fertilizers, pesticides, fungicides and salt deicers on sidewalks and roads.

Mulch can help eliminate weeds under the rhododendron. Not only does it lessen the workload, but it reduces the competition for moisture, nutrients and sunlight. Besides, removing the weeds can cause damage to shallow rooted plants. It helps prevent the spreading of disease spores by foot traffic, and some mulches even repel insects and combat diseases.

One of the most beneficial aspects of mulching is the improvement it brings to structure and fertility of the soil. Mulching establishes a cool, moist environment where bacteria and other microorganisms (e.g., worms) can aid in the decomposition process. This process, among many other things, produces humic acid, which helps release bound-up materials such as phosphorus and iron to the soil, carbon dioxide to the plant for use in food production and ammonia, a form of nitrogen plant food, to the plant.