The Pros and Cons of Lava Rock As Mulch

As an inorganic mulch, lava rock is a non-native material that aids plant growth when spread around the plant. While lava rock succeeds at the main mulching goals -- soil moisture and weed prevention -- it will never melt into the environment like organic mulches.

Benefits

The primary benefits of lava rock mulch is its lifespan. Unlike organic mulches such as bark that need frequent replacement, lava rock can last for years. Its porousness may also enable it to insulate the soil. Lava rock is just as effective as other mulches at keeping soil moist, according to an Iowa State University study comparing the effects of five types of mulches on red maple tree growth.

Concerns

Lava rock poses a concern to gardeners who only want to use recycled, organic materials in their gardens. Its weight frequently causes soil compaction, according to forestry specialist Michael Kuhns on Utah State University's website. This results in less oxygen and water for plants.

Function

Lava rock is a convenient mulch for gardeners who want to apply mulch and leave it for long periods of time. Although it does not add nutrients to the soil, it succeeds in its main goals and is easy to apply.

References

• University of Florida Extension: Mulching Practices for South Florida
• Utah State University Forestry Extension: Mulching is Important for Tree Health
• Iowa State University: Effect of Organic and Mineral Mulches on Soil Properties and Growth of Fairview Flame Red Maple Trees
• University of Florida IFAS Extension: Mulch is Ideal for Establishing Trees, But Do It Right