Avocado Mulch and Compost Demonstration: University of California, Riverside

In November 1997, the California Integrated Waste Management Board (CIWMB) (now known as the California Department of Resources Recycling and Recovery or CalRecycle) initiated a contract with the University of California at Riverside (UCR) for a two-year continuation of a demonstration and research project using mulch and compost in Southern California. The area of investigation was expanded to include field plots in Ventura (past and present work), Santa Barbara, San Diego, and Riverside counties for a total of four commercial avocado and three commercial citrus sites. CIWMB funding, which totaled $87,500 plus cash or equipment contributions from three local governments (City of Los Angeles, County of Santa Barbara, and City of San Diego), allowed project staff to conduct research at the seven mulch and compost demonstration sites using products made primarily from municipal yard trimmings. Two CalRecycle publications are available:


  • Evaluate Phytophthora root rot suppression in California avocado and citrus orchards.
  • Collect data on mulch and compost as surface applications under young and old trees.
  • Characterize plant available nutrients and other properties of these recycled-content products and their effects on avocado and citrus production.

Partnership Organizations

  • Fiscal Agent: University of California, Riverside.
  • Project Director: John Menge, UCR Department of Plant Pathology.
  • Key Partners: Ventura County UC Cooperative Extension, UCR Dept. of Environmental Science, Debonne Ranch Management, Pommer Ranch, Essick Ranch, Vedder Ranch, Powell Ranch, Vanoni Ranch, Sprinkling Ranch, Community Alliance with Family Farmers, Resource Conservation District of Greater San Diego County.

Project Components

  • Partnership Development and Implementation of Work Plan. The partnership team developed a work plan for evaluating the use of mulch and compost in commercial avocado and citrus production. Tasks performed included investigating pneumatic spreading of materials, evaluation of tree growth and yield, effect of mulching on soil moisture and weed suppression, and the impact on Phytophthora root rot relative to mulch or compost use through 1998.
  • Development and Dissemination of Information. During the course of the project, the partnership developed and disseminated several news releases and trade publication articles. The principal researchers plan to publish articles in scientific journals.
  • Coordination of Field Days. The partnership team conducted four field days at multiple demonstration sites and one compost workshop for growers during the course of the contract in the four-county project area.
  • Reporting and Publishing Results. During the course of the project, the partnership team leader reported on progress of the research project and submitted a final report on the avocado and citrus demonstration.


  • Demonstrate the value of mulch and compost use in avocado and citrus production.
  • Increase the field research plot locations and build upon the data accumulated in the previous three years of research on growth, yield, and disease suppression.
  • Disseminate the results of the project to commercial avocado and citrus growers.

For more information contact: Compost Use in Agriculture, organics@calrecycle.ca.gov