Compost Tea: Miracle Cure or Marketing Gimmick?
Compost Tea – An Introduction
Compost tea is a liquid extract produced by diluting compost with water. Anecdotal evidence
suggests these teas may be effective against pathogens associated with foliar and fruit
diseases. The theory is that bacteria, fungi, and other components in the tea act as biological
controls. These organisms may work by inducing plant resistance, inhibiting pathogen growth,
or outcompeting the pathogens. Some compost teas apparently contain large numbers of
beneficial microbes that compete for space on leaves and fruits, denying pathogens space to
colonize. Others apparently contain antimicrobial chemical compounds produced through
decomposition and inhibit pathogen growth. However, few controlled, replicable scientific
studies exist to support claims of the tea's effectiveness.
In addition, the potential exists for high nutrient loading of soils when such teas are used as
fertilizer. Unlike compost used for mulch, which provides a slow release of nutrients, compost
teas most certainly add increased levels of nitrogen, potassium, and other minerals all at once.
It is unlikely that these are completely absorbed by the plants and instead may contribute to the
eutrophication of watersheds.
A lack of consistency in compost age and ingredients and tea preparation and application
methodology makes evaluating claims of efficacy difficult and often leads to inconsistent and
conflicting results. Variations in weather patterns can affect rates and severity of
pathogen/disease damage, and therefore “effectiveness” of compost teas. Before any benefit
can be attributed to a specific compost tea, the following criteria must be defined (and
• What is the age and source of the compost? What organic material is present?
• What is the method of preparation (aerobic vs. fermented)?
• What are the chemical properties of the compost (pH, % nitrogen, etc.)?
• What are the active ingredients?