Compost Tea: Science, Skepticism, and How to Brew Your Own

Compost tea's value is debated. Organic proponents cite healthy plots and beneficial microbes. Agricultural scientists note lack of rigorous experiments or studies showing no benefit. Home gardeners can choose their faith and experiment—or not.

The Basics: Bag-in-a-Bucket

Low-tech, decades-old method: shovelful of finished compost in burlap sack, submerged in a bucket (giant tea bag), steeped days. Water-soluble nutrients and microorganisms leach out. Dilute dark liquid to tea color. Drench soil or spray leaves.

Theory: compost tea inoculates soil and leaf surfaces with "good" organisms that crowd out pathogens—analogous to human probiotics. Anecdotal evidence supports this.

The Scientific View

Scientists want hard evidence. Poor compost = poor tea. Improper handling = low microbe counts. Controlled experiments are hard on a variable product. Current data shows limited success. Dr. Linda Chalker-Scott's "Compost Tea: Examining the Science Behind the Claims" presents the scientific perspective.

To Brew or Not to Brew?

Summer's mild weather makes managing this biologically active extract easier. Use as gentle liquid fertilizer/soil booster—no burn risk like synthetic fertilizer. Gardens need watering anyway.

Modern standard: aerated compost tea (ACT). Basic recipe enhanced with microbial food source and mechanical oxygenation. When done well, microlife multiplies manyfold, allowing inoculation of larger areas than spreading limited compost.

Decide: wait for overwhelming controlled evidence? Skip the rest. Want to experiment? Read on.

Critical Points for Home Brewing

• Use only good-quality, well-aged, finished compost.
• Be extra cautious on food crops—E. coli and Salmonella documented in ACT.
• Aerated teas need vigorous aeration and limited brew time, or they "spoil" (good organisms die).
• Use unchlorinated water only.
• No fresh manure; caution with manure composts unless effectively hot-composted.

Resources

• Steve Diver's "Notes on Compost Teas" – in-depth treatment, links, aeration setup help.
• Soil Foodweb Inc. – Dr. Elaine Ingham's ACT recipe (advises against molasses as bacterial food).
• Search tip: Google site:.edu "compost tea" for university research.