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To produce a highly beneficial compost tea, you first
need to start with quality ingredients (feedstocks). There are several
production methods you can choose from, based on your scale and needs. It's
important to understand the needs of your plants and soil. and you may need
to choose a method based on your application method.
The basic feedstocks for compost tea are compost, water,
and other additives.
Quality Compost
You must start with high quality, fully finished compost. Compost products
will vary in quality based on the original
feedstock and the conditions under which it is decomposed. For small-scale
composting,
feedstocks would include yard trimmings,
grass clippings, wood chips, dry leaves, fruit and vegetable scraps, paper
products—even untreated wood chips and sawdust.
To learn about making quality compost on a small scale, including
information on bins and piles, ingredients, techniques, and troubleshooting,
please see our home composting guide. You might also be interested in more detailed information about
characteristics of different
types of compost for different situations.
Pure Water
It is important
to use water that is as pure and as uncontaminated as possible. Water
containing high levels of salts, heavy metals, nitrates, pesticides,
chlorine or
pathogens should not be used. These will affect the survival and
reproduction of beneficial organisms from the compost and may also adversely
affect the plants on which the compost tea is applied.
Additives
Certain stimulatory additives can be included during brewing to improve
the final quality of the compost tea. These are materials that are added in
the process of making compost tea (as distinct from spray adjuvants
that are tank mixed immediately prior to application) and that are presumed
to sustain and enrich microbial growth. Examples
include (but are not limited to) molasses, yeast extract, fish-based products, kelp, and
green plant tissue.
The debate that has been brewing in the
compost tea world centers on whether the introduction of simple sugars (such
as molasses) to rapidly increase the microbial population of
compost tea creates a too-hospitable environment for harmful
pathogens, such
as strains of E. coli and Salmonella.
One side of the debate argues that such pathogens would only multiply if
they had been present in the compost in the first place. Another side warns
that agents change the original compost product and set up too many unknown
variables, such as rapid fermentation.
These include materials such as kelp, rock dust,
molasses, humic and/or
fulvic
acids, and commercially available
microbial spore suspensions. Solid
materials, such as rock dust, must be added to the compost in the tea bag,
while soluble materials, such as molasses, should be added to the water.
For more information on understanding these additives which you may
wish to use:
Erring on the side of caution, the Compost Tea Task Force has set up separate, more restrictive
guidelines for those who use "compost tea additives" in their brews than for
those who do not.Top of Page
Other Considerations
In addition to high quality feedstocks, you should also
consider the following factors when choosing a production method and making
your compost tea.
Characteristics of the "Tea Bag"
The mesh size of
the "tea bag" will determine which components of the compost are extracted into
the water. With a fine mesh bag, only the tiny, soluble components will
enter the water. This is critical if the compost tea will be applied with a
sprayer or in irrigation systems. Farmers and researchers have found that
old nylon stockings make fine tea bags, though fine-weave cotton and silk
will also work. Nylon window screening, plastic feed bags, and burlap can
also be used. It is important to use clean material for the tea bag that is
not treated with any preservatives or other chemicals.
Aeration and Recirculation
It is important
to choose an aeration system that will provide the proper amount of water agitation.
When compost tea is not adequately agitated, oxygen can become depleted
thereby
reducing aerobic microbial growth,
creating anaerobic conditions,
and
resulting in poor extraction of materials from the compost.
Ratio of Compost to Water
If there is too
much water for the amount of compost, the tea will be dilute and will not
provide maximum benefits. However, if there is too much compost, it is
possible that there will be an excess of nutrients for bacteria, which can
lead to oxygen depletion and anaerobic conditions. It is important to
experiment with different quantities in your system to achieve the best
ratio.
Brew Time
The longer the
compost remains suspended in the water, the greater the amount of soluble
materials that will be extracted from the compost. These include both living
organisms and the nutrients that will feed them. Compost tea that is well-aerated and recirculated will require a shorter brewing time than tea made
without adequate agitation. Using a sophisticated micro-brewing system, it
is possible to produce good quality compost tea in 18 to 24 hours. Under
more basic conditions, it may be necessary to allow the compost to steep for
a few days to a few weeks.
Environmental Conditions
Temperature,
humidity, and evaporation all can affect the quality of the compost tea. If
water is too cold, extraction will be reduced and microbe growth slowed, but
if it is too warm, microorganisms may be inhibited or excessive evaporation
may occur. It is hard to change the ambient weather, but a cover over the
container in hot weather should help control evaporation.
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Depending on your scale of production and the level of
financial resources available to purchase commercial brewing equipment vs.
making some kind of homemade brewer, there are several methods to choose
from.
Bucket Fermentation Method
"Passive" compost tea is prepared by immersing a burlap sack filled with
compost into a bucket or tank and stirring occasionally. Usually the brew time
is from 7 to 10 days. This is the method that dates back hundreds of
years in Europe, and is more akin to a compost watery extract than a
“brewed” and aerated compost tea.
Bucket Bubbler Method
The equipment setup and scale of production are similar to the bucket
method, except that an aquarium-size pump and air bubbler are used in
association with microbial food, and catalyst sources added to the solution
as an amendment. Since aeration is critical, as many as three sump pumps may
be used in a bucket simultaneously.
With homemade compost tea brewing, a compost "sock" is commonly used as a
filter-strainer. Ideally, the mesh size will strain compost particulate
matter but still allow beneficial microbes—including fungal hyphae and
nematodes—to migrate into solution. Single-strand mesh materials such as
nylon stockings, laundry bags, and paint bags are some of the materials
being used; fungal hyphae tend to get caught in poly-woven fabrics. If
burlap is used, it should be “aged” burlap.
Trough
Method
Large-scale production of compost teas employs homemade tanks and pumps. An
8- or 12-inch-diameter PVC pipe is cut in half, drilled full of holes, and
lined with burlap. Compost is placed in this makeshift trough. The PVC
trough is supported above the tank, several feet in the air. The tank is
filled with water and microbial food sources are added as an amendment. A
sump pump sucks the solution from the bottom of the tank and distributes the
solution to a trickle line running horizontally along the top of the PVC
trough filled with compost.
As the solution runs through the burlap bags
containing the compost, a leachate is created which then drops several feet
through the air back into the open tank below. A sump pump in the bottom of
the tank collects this "tea" and distributes it back through the water line
at the top of the trough, and so on. Through this process, which lasts about
seven days, the compost tea is recirculated, bubbled, and aerated. The
purpose of the microbial food source is to grow a large population of
beneficial microorganisms.
Commercial Tea Brewers
Commercial equipment is available for the production of brewed compost teas. Usually there is a compost sack or a
compost leachate basket with drainage holes, either of which are used to
hold a certain volume of compost. The compost-filled container is placed in
a specially designed tank filled with chlorine-free water. Microbial food
sources are added to the solution. A pump supplies oxygen to a
specially-designed aeration device which bubbles and aerates the compost tea
brewing in the tank.
Note: Research at
Soil Foodweb, Inc. in Corvallis, Oregon has shown that differences exist
in the beneficial attributes of compost teas, with commercial tea brewers
producing the greatest numbers and diversity of beneficial microorganisms.
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