Compost tea, generally defined as a liquid extract of compost, has
gained acceptance by homeowners and commercial growers around the
world for its ability to stimulate soil biological activity, improve
soil structure, and enhance overall plant health and vigor. Reported
benefits of using compost tea include enhanced disease suppression,
reduced fungicide and fertilizer requirements and associated cost
savings. Research efforts to validate these benefits are expanding.
The contemporary compost tea industry by and large uses the term
"compost tea" in reference to an aerated extraction process.
Historically, the term "compost extract" (among others)
was used to describe an extraction process that may or may not include
active aeration. Until very recently, almost all published research
on the benefits of compost extracts pertained to non-aerated processes.
The first known commercially available industrial-grade, aerated
compost tea system was introduced in the United States in 1997.
There are now several compost tea systems on the market with a range
of features and capacities, reflecting growing demand for these
systems and the inception of a new industry.
Aerated compost tea systems are designed to consistently provide
optimum conditions for extraction and proliferation of beneficial
aerobic microorganisms present in the starting compost, as well
as extraction of the components from the compost that are either
soluble or able to be held in suspension. In almost all compost
tea production scenarios, compost or vermicompost is the source
of organic matter, organisms and nutrients for extraction. The resulting
tea is therefore directly influenced by the characteristics of the
Though designs vary, most commercial aerated tea systems consist
of a tank, a mesh container/filter for holding compost, and an aeration
system. The ratio of compost to water varies with the system, but
in one example approximately 5-7 pounds of compost is used in 25
gallons of water to make a concentrated product that can then be
further diluted depending on the application. The typical extraction
period for aerated compost tea is 24 hours. Most commercial tea
production includes the addition of supplemental microbial food
sources to enhance microbial growth and diversity. Research and
experimentation are ongoing among compost tea users to assess the
effects of these supplemental foods.
Compost tea has many of the same beneficial attributes of compost,
but it is clearly a different product. Unlike compost, it can be
applied directly to plant foliage, providing nutrition and beneficial
microorganisms that colonize leaf surfaces. This is thought to be
instrumental in the disease suppression capabilities of compost
tea. Compost tea applied directly to the soil is a way to boost biological activity when application of solid
compost is not practical, or as a supplement between compost applications.
Because it is a relatively new industry, the body of knowledge on
aerated compost tea systems is not expansive. Enthusiastic feedback
from users indicates a strong demand for more scientific information
and practical guidance. As in compost production, there are a number
of variables that influence the ability to make a consistent batch
of compost tea. Aerated compost tea system manufacturers have made
progress in controlling critical mechanical variables such as aeration,
extraction, mixing, temperature, cleaning and scheduled maintenance.
Further progress is needed to effectively manage the remaining variables,
to identify specific biological mechanisms responsible for the beneficial
effects of compost tea, and to identify appropriate application
strategies in specific cropping systems.