Mulch is a protective layer of material, typically consisting of organic substances like wood chips or shredded bark. It serves multiple purposes, primarily regulating soil temperature and conserving moisture by reducing evaporation. A common point of confusion immediately after application is whether the fresh layer of mulch needs to be watered to begin its job effectively.
The Immediate Need for Watering
Mulch should be watered immediately after application to ensure it begins performing its function. This initial watering is important for bagged, dried organic mulches, such as shredded wood or bark, which contain very little moisture. Dry material can repel water, hindering its ability to settle and protect the soil beneath it. The goal is to thoroughly moisten the mulch layer itself, not necessarily to saturate the underlying soil, which should be watered beforehand. Applying about one inch of water helps achieve saturation and makes the mulch heavy enough to resist displacement by wind.
How Watering Settles and Activates Mulch
The act of wetting the mulch serves two major purposes: physical settling and biological activation. Water helps the organic particles interlock and compact slightly, preventing the mulch from being blown away by wind. This settling creates a cohesive, uniform layer that acts as a better insulator for the soil below. Water is also necessary to initiate the microbial breakdown process. Moist mulch encourages the growth of beneficial fungi and bacteria, which begin the slow process of decomposition. This process releases nutrients into the soil over time and improves the soil’s structure. Ensuring the mulch is hydrated from the start sets the stage for this long-term biological benefit.
Mulch Hydration and Moisture Management
Once the mulch is settled and activated, the management of water shifts to long-term maintenance. The established layer of mulch is highly effective at slowing water loss from the soil. This moisture retention means the frequency of watering for the plants beneath the mulch can be significantly reduced.
One potential issue that can arise, especially with aged wood chips, is hydrophobicity, where the mulch surface repels water. If a layer becomes too dry, the waxy organic compounds on the material’s surface can cause rainfall or irrigation to bead up and run off the top instead of penetrating through to the soil. If this occurs, a soil-wetting agent or light raking of the surface may be necessary to break the water-repellent barrier.
For ongoing care, the best practice is to check the moisture level under the mulch layer by inserting a finger a few inches into the soil. The soil beneath should feel damp, but not waterlogged, a sign that the mulch is doing its job correctly. When watering is necessary, it should be a deep, thorough soaking aimed at the base of the plants to ensure the water moves through the mulch and into the root zone, rather than a light sprinkling that only moistens the mulch surface.