Compost Tea - Anyone for a cup?
There are 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 micro-organisms.
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 and kelp 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.
Liquid manures can be a blend of marine products (seaweed extract, kelp meal) and locally harvested herbs (stinging nettle, comfrey), 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 compounds.
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 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 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.