many methods and materials you can use, but the basic rule of
thumb is to dilute any liquid you have made until it looks like
weak tea before using on the garden.
Compost tea makes the benefits of compost go farther. What's
more, when sprayed on the leaves, compost tea helps suppress
foliar diseases, increases the amount of nutrients available to
the plant, and speeds the breakdown of toxins. Using compost tea
has even been shown to increase the nutritional quality and
improve the flavour of vegetables. If you've been applying
compost to your soil only in the traditional way, you're missing
out on a whole host of benefits
Compost watery extract—made from compost
suspended in a barrel of water for 7 to 14 days, usually soaking
in a burlap sack or Hessian bag—a centuries-old technique. The
primary benefit of the extract will be a supply of soluble
nutrients, which can be used as a liquid fertilizer.
Compost tea, in modern terminology, is a compost extract brewed
with a microbial food source—molasses, kelp, rock dust, humic acids. The compost-tea brewing technique, an
aerobic process, extracts and grows populations of beneficial
Compost teas are distinguished from compost extracts both in
method of production and in the way they are used. Teas are
actively brewed with microbial food and catalyst sources added
to the solution, and a sump pump bubbles and aerates the
solution, supplying plenty of much-needed oxygen. The aim of the
brewing process is to extract beneficial microbes from the
compost itself, followed by growing these populations of
microbes during the 24- to 36-hour brew period. The compost
provides the source of microbes, and the microbial food and
catalyst amendments promote the growth and multiplication of
microbes in the tea. Some examples of microbial food sources:
molasses, kelp powder, and fish powder. Some examples of
microbial catalysts: humic acid, yucca extract, and rock dust.
Liquid Organic Extracts vs. Compost Teas
Building on the concept of compost teas as a liquid organic
extract, what are some other common organic extracts used as a
liquid drench or foliar spray?
Manure-based extracts—a soluble nutrient source made from raw
animal manure soaked in water. For all practical purposes,
manure tea is prepared in the same way as the compost extracts
described in the preceding section. The manure is placed in a
burlap sack and suspended in a barrel of water for 7 to 14 days.
The primary benefit of the tea will be a supply of soluble
nutrients, which can be used as a liquid fertilizer.
Plant-based extracts—stinging nettle, horse tail, comfrey,
clover. A common method is to stuff a barrel about
three-quarters full of fresh green plant material, then top off
the barrel with tepid water. The tea is allowed to ferment at
ambient temperatures for 3 to 10 days. The finished product is
strained, then diluted in portions of 1:10 or 1:5 and used as a
foliar spray or soil drench. Herbal teas provide a supply of
soluble nutrients as well as bioactive plant compounds.
Mixtures of plant and animal byproducts steeped as an
extract—stinging nettle, comfrey, seaweed, fish wastes, fish
meal. Liquid manures are a blend of marine products (local fish
wastes, seaweed extract, kelp meal) and locally harvested herbs,
soaked and fermented at ambient temperatures for 3 to 10 days.
Liquid manures are prepared similarly to herbal tea—the material
is fully immersed in the barrel during the fermenting period,
then strained and diluted and used as a foliar spray or soil
drench. Liquid manures supply soluble nutrients and bioactive
Compost teas and herbal teas are tools that can be made on the
farm to enhance crop fertility and to inoculate the phyllosphere
and rhizosphere with soluble nutrients, beneficial microbes, and
the beneficial metabolites of microbes.
The composting process—thermophyllic heating to
60-90° C for 10-15 days—assures pathogen reduction in manures
added to compost. The raw
organic matter initially present in the compost windrow
undergoes a complete transformation, with humus as an end
product. Any pathogens associated with raw manures will be gone.
So caution is extended: Manure teas are NOT the same thing as
compost teas or compost extracts. Because of concerns over new
pathogenic strains of E. coli, the author advises growers to
reconsider manure teas and/or to work with a microbial lab to
ensure a safe, worthwhile product.
Methods of Compost Tea Production
"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
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 20- or 30cm-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 (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.
The science behind compost tea
The soil is full of micro-organisms that aid plant growth and
plant health--bacteria and fungi, which are decomposers, and
protozoa and beneficial nematodes, which are predators. But
there are bad guys, too--disease-causing bacteria and fungi,
protozoa, and root-feeding nematodes. Our goal as gardeners is
to enhance the beneficial micro-organisms in this soil foodweb,
because they help our plants.
The bad bacterial
decomposers and the plant-toxic products they make are enhanced
by anaerobic, or reduced-oxygen, conditions. By making sure the
tea and the compost itself are well oxygenated and highly
aerobic, you eliminate 75 percent of the potential
plant-disease-causing bacteria and plant-toxic products. To take
care of the other 25 percent of potential diseases and pests,
you want to get good guys into the soil and on at least 60 to 70
percent of your plants' leaves. Good bacteria work against the
detrimental ones in four ways: They consume the bad guys, they
may produce antibiotics that inhibit them, they compete for
nutrients, and they compete for space.