As the name implies, compost tea is made by steeping compost in water.
It's used as either a foliar spray or a soil drench, depending on where
your plant has problems.
“Passive” compost tea is prepared by immersing a burlap sack filled
with compost into a bucket or tank, stirring occassionally. Usually the brew
time is longer, 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.
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 polywoven fabrics. If burlap is used,
it should be “aged” burlap.
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
Commercial equipment is available for the production of brewed compost teas (see
a list of suppliers below). 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.
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. 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.
By Steve Diver
NCAT Agriculture Specialist