Science-based Landscape Mulching Information for Inland Southern California

The information provided here is based on a field research experiment conducted at the University of California, Riverside, by Dr. Verdi's research group in 2025-2026.

Important notes:
  • The rainfall-capturing potential reported here should be interpreted with caution. These ratings were inferred from soil moisture sensor responses after rainfall events. Runoff was not directly measured, so the results should be viewed as an indicator of how much water appeared to enter and remain in the soil, not as a direct measurement of stormwater capture.
  • Mulch selection should also consider weed control. Weed suppression was not evaluated in this study, but it is an important practical factor when choosing mulch materials for landscapes.
  • Longevity is another important consideration. Inorganic mulches, such as rock or gravel, are generally expected to last longer than organic mulches. Organic mulches can break down over time and may need to be reapplied or supplemented periodically. This study did not evaluate mulch longevity or replacement cost, but these factors should be considered in real-world mulch selection.
  • Given recent wildfire concerns in Southern California, inorganic mulches may also have an advantage over organic mulches because they are non-combustible. However, wildfire behavior was not directly evaluated in this study, and independent testing would be needed before making fire-safety recommendations.
  • Most mulch materials used in this study, except synthetic turfgrass and rubber mulch, were purchased from Southern California Mulch Inc. The vendor name is provided for information only and does not imply endorsement.
  • All rock materials used in this study were small, approximately 3/8 inch in size. The same rock materials in larger sizes may perform differently because particle size can affect water movement, surface coverage, evaporation reduction, and rainwater-capture potential.

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