Residential outdoor water use contributes significantly to water consumption nationwide. Given our dry conditions in 2024, it’s more important than ever to reduce our water usage outside.
Homeowners can take action steps such as allowing yards to go dormant, installing alternative lawns, or growing native drought-tolerant plants.
One effective (yet often oversimplified) water saving method is using mulch, which can notably enhance water retention in landscapes. However, with the numerous mulch types available, which are actually best for conserving water?
What is mulch?
Technically, mulch is any material (organic or inorganic) applied over the soil’s surface. When soil is left bare, a crust can form, obstructing water’s infiltration to plant root zones. Mulching allows soil structure to remain intact and can improve water retention.
Additionally, weed suppression, stabilized soil temperatures, and reduced water runoff are other benefits of mulching. Organic mulch even provides nutrients to the soil as it decomposes.
Diversity of mulches
Mulch can be anything from wood chips to pea gravel. And often when discussing the benefits of mulches (i.e., improving water retention) the type of mulch is not mentioned. This can lead to some unfortunate misunderstandings, because in reality, not all mulch types reduce water use.
The overview below aims to identify which organic mulches may or may not effectively support water conservation:
Bark: Many users prefer bark mulch for its cohesive aesthetics, but it contains suberin, a waxy substance that repels water and hinders soil moisture movement. While both coarse and fine bark enrich the soil as they decompose, they can also introduce weeds, with fine bark mulches often leading to outbreaks of horsetail.
Sawdust: Sawdust offers a uniform aesthetic and is often cheaper and more accessible than bark. However, its fine texture can compact easily, causing water repellency and preventing oxygen movement in the soil. Coffee grounds, like bark, can also lead to compaction. Both are generally better suited as soil amendments or compost pile additions.
Wood chips: Wood chip mulch is made up of the inner wood of trees making it good at holding moisture. Wood chips are often more available and affordable than bark mulches. Its absorbent nature allows water movement to the soil. Wood chips do turn gray in color over time and need to be reapplied every few seasons.
Pine needles, leaves and grass clippings: All of these mulches can usually be found in your own yard and provide great protection in shrub and flower beds during colder months, especially if applied in late fall after the soil starts to freeze. Be aware that shredded leaves and grass clippings if applied wet, can become mat-like and start to impede water infiltration.
Mulching tips
Overall, wood chip mulch is usually seen as the best for soil water retention. Applying mulch can be extremely beneficial for your landscape and understanding the pros and cons of different mulches is essential to actually reducing water use. Timing and thickness of application is also important.
In general, apply in the springtime once the soil has started warming at least 2-4 inches deep over weed free and deeply watered soil.
Never apply mulch to dry soil! Get in the habit of checking your soil moisture with your finger.
For more tips on mulching and water conservation, and to stay updated on local water management efforts, water events and the 2024 drought, visit extension.wsu.edu/clallam/water-conservation.
Sammi Grieger is the Water Conservation Coordinator at the WSU Clallam County Extension Office in Port Angeles. Contact her at samantha.grieger@wsu.edu.
