Reports on a two-year research project designed to investigate the value of using raw yard trimmings or compost as mulch in avocado and citrus trials over a four-county area of Southern California. A key benefit noted was a reduction in avocado root rot caused by Phytophthora cinnamomi. University of California staff and farm advisors analyzed data that related to tree growth, soil moisture, nutrients, microbial activity and associated enzymes, crop yield, rodents, nematodes, weed control, and disease suppression.