Mulch is a layer of material spread over the soil to maintain moisture, regulate soil temperature, and improve soil health. While applying this layer is straightforward, many people wonder if a fresh layer of mulch requires watering immediately after application. The short answer is yes; watering new mulch is generally beneficial and necessary to ensure it performs its intended functions effectively from day one.
The Necessity of Initial Watering
The primary purpose of watering a newly applied layer of organic mulch is to help it settle and compact into a cohesive layer. Dry, lightweight materials like shredded bark or wood chips are highly susceptible to being blown away or displaced by wind or heavy rain. A thorough initial watering adds weight to the material, causing the individual pieces to interlock slightly and creating a stable barrier that resists displacement.
Preventing Hydrophobicity
Initial moisture application also addresses hydrophobicity, a condition where very dry organic material actively repels water. When wood-based mulches become extremely dry, fungi can colonize the material and create a waxy, water-repellent coating. If this occurs, rain or irrigation water will bead up and run off the surface instead of penetrating the mulch and reaching the soil beneath. Watering the mulch immediately helps prevent this condition by ensuring the material is already moist, allowing for proper water absorption and flow down to the soil level.
How Mulch Type Affects Watering
The composition of the mulch material significantly dictates the urgency and necessity of initial watering.
Organic Mulches
Organic mulches, which include shredded wood, bark chips, and straw, require the most attention because their material properties change when wet. These materials rely on moisture to bind together, initiate the slow process of decomposition, and avoid the hydrophobic state. Finely shredded organic mulches, such as processed wood products, are particularly prone to becoming hydrophobic when dry and demand a thorough soaking to ensure penetration.
Inorganic Mulches
Conversely, inorganic mulches, which are materials like stone, gravel, or rubber, typically do not require watering for settling or to prevent hydrophobicity. These materials gain weight from their inherent density and do not absorb water. The only reason to water inorganic mulch is for aesthetic purposes, such as rinsing away any fine dust or dirt accumulated during the spreading process.
Proper Post-Application Watering Technique
The technique used for this initial soak is important. The goal is to saturate the mulch layer itself without oversaturating the soil underneath, which should have been adequately watered before the mulch was applied. A gentle spray or shower setting on a hose nozzle is the ideal method, as a high-pressure jet can easily displace the new material.
The volume of water should be enough to make the mulch moist throughout its entire depth, which is typically a 2 to 4-inch layer. This may be equivalent to providing about one inch of water across the mulched area. The initial watering is generally a one-time, deep soak intended to lock the material in place and prevent dry-out, and it is distinct from the regular irrigation schedule that the mulch layer is designed to reduce.