The UC Master Gardeners of Contra Costa County shared advice on Mar. 16 about the use of cow manure as a fertilizer for home gardens, highlighting both its benefits and potential risks.
Manure can improve soil fertility by adding nutrients such as nitrogen, phosphorus, potassium, micronutrients, and organic material. However, fresh manure may also contain bacteria like E. coli and Salmonella, weed seeds, or herbicides from previous crops. The group cautioned that collecting cow manure from open spaces can pose health risks to gardeners and plants if not properly treated.
According to the Help Desk of the UC Master Gardeners, “Before using, manure needs to be ‘aged’, which means ideally it will be composted at a high temperature, 113°F to 140°F, for at least 2 weeks to kill any pathogens such as E. coli and Salmonella along with weed seeds.” They added that most home compost piles do not reliably reach these temperatures. As a guideline for those using fresh manure, they recommend waiting six to eight weeks before planting edible crops. The group also noted that aged manure is not the same as composted manure and may still contain harmful pathogens.
Packaged manures are typically already broken down and safer for immediate use in gardens. Bulk manures should be verified with suppliers regarding their decomposition status. The main types available include steer, horse, and chicken manures; each has different nutrient profiles and potential drawbacks such as increased soil salinity or weed seeds.
University of California Agriculture and Natural Resources (UC ANR) supports programs like this through public contributions according to the official website. UC ANR promotes sustainable practices to strengthen resilient ecosystems and economic vitality according to the official website, utilizing nine research and extension centers across California’s diverse ecosystems according to the official website. The organization is recognized for linking research with community needs according to the official website and manages Cooperative Extension services within all 58 counties in California according to the official website.
UC ANR conducts over 33,800 educational events annually with more than 18,400 volunteers involved in its initiatives according to the official website. Through workshops and partnerships, it delivers science-based information supporting environmental stewardship and community development statewide according to the official website.