When compost tea is sprayed on a plant, the plant will often grow more vigorously, resist disease and insect attack, and may produce higher yields of flower and fruit.  While chemical pesticides work by killing microorganisms, both the pathogenic and the beneficial ones, compost tea works on a very different principle.  Inoculation of the soil with beneficial organisms can help to release plant available nutrients, aid the decomposition and recycling of soil organic matter, improve soil structure, and add beneficial organisms to the soil.  The soil is full of microorganisms, such as bacteria, fungi, protozoa, and nematodes, and can aid plant growth..  Soil also contains disease causing bacteria, fungi, protozoa, and root feeding nematodes.  The goal for using compost tea is to enhance the beneficial microorganisms in the soil.

 

The harmful bacterial decomposers and the plant toxic products they make are enhanced by anaerobic or reduced oxygen conditions.  By making sure the tea and compost are well oxygenated and highly aerobic you eliminate 75% of the potential plant disease causing bacterial and plant toxic products.  To take care of the other 25% of the potential diseases and pests, get good microorganisms into the soil as well as on at least 60% – 70% of the plants’ leaf surface.  Good bacteria work against the detrimental ones in four ways: they consume the bad bacteria, they may produce antibiotics that inhibit them, they compete for nutrients, and they compete for space.   

 

Making Good Compost Tea

To make good compost tea, start with actively managed, mature compost that has been turned a few times and allowed to heat adequately to kill weed seeds and pathogens.  Worm compost also makes excellent tea without the hassle of turning or checking the temperature.  Add to the finished compost a little forest floor debris. Then fill a 5 gallon plastic bucket half full of the compost.  Metal containers are not recommended because the compost tea can corrode some types of metal.  Compost tea should not be made from manure-based compost unless the pile temperature exceeds 135º F for at least 10 to 14 days and the compost is carefully made to ensure uniform heating.  Deadly pathogenic bacteria are also killed at this temperature.

 

Tea Bag

Next, transfer the compost into a ”tea bag” made from an old nylon stocking, pillowcase, plastic mesh feedbag, nylon window screening, or burlap.  It is important to use a clean material for the tea bag – one that has not been treated with any chemicals.  The mesh size of the tea bag will determine what components are extracted into the water.   With a fine mesh bag, only the tiny, soluble components will enter the water.  This is important if the compost tea will be applied with a sprayer or in an irrigation system. 

 

Tea Water

The bag is then suspended in the 5-gallon bucket, half full of water.  Fill the bucket to within 3 inches of the rim with water.  It is important to use water that is as pure and as uncontaminated as possible, such as rainwater, well water, or well-aerated tap water.  Water containing high levels of salts, heavy metals, nitrates, pesticides, chlorine, or pathogens, should not be used because they will affect the survival of beneficial organisms in the compost and may also affect the plants on which the compost tea is applied.

 

Aeration System

If the tea is not aerated constantly, the organisms in it will quickly use up the oxygen and the tea will start to stink and become anaerobic.  An aquarium aerator can be used to add sufficient air to the water.  Cut a length of plastic tubing that comes with the aerator pump kit and attach one end to the pump and the other to a gang valve.  Cut three more lengths of tubing long enough to reach comfortably from the rim to the bottom of the bucket.  Connect each one to a port on the gang valve and push an aeration bubbler on the other end.  Hang the gang valve on the lip of the bucket and bury the bubblers at the bottom, under the tea bag.  It is important to choose a system that will provide the proper amount of water agitation and aeration.  When compost tea is not adequately agitated, oxygen can become depleted, resulting in poor extraction of material from the compost.

 

With the bubblers working, add 1 oz. of organic, unsulfured molasses to the water and stir vigorously with a stick.  The molasses feeds the bacteria and gets the beneficial species to flourish really well.  After stirring, rearrange the bubblers so they are on the bottom and well spaced.  Try to stir the tea at least a few times a day.  A vigorous mixing with the stick shakes more organisms loose and into the tea.

 

There are more sophisticated compost tea micro-brewing systems on the market, and these are designed to optimize aeration and recirculation by swirling the water around the compost in a continuous vortex.  The high tech approach reduces the time required to produce a good quality, microbially diverse compost tea, and it is especially valuable in producing large quantities of compost tea commercially.  Using these sophisticated micro-brewing systems, it is possible to produce good quality compost tea in 18 to 24 hours. 

 

Brew Time

The longer the compost remains suspended in the water, the greater the amount of soluble materials 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.  If you leave the tea steeping for more than 3 days, more molasses must be added or the good organisms will start going to sleep because they don’t have enough food to stay active. 

 

Environmental Conditions

Temperature and evaporation affect the quality of the compost tea.  If the water is too cold, extraction will be reduced and microbe growth will be slower, but if it is too warm, microorganisms may be inhibited or excessive evaporation may occur.  It is hard to change the weather, but a cover over the container in hot weather should help control the evaporation.

 

Application

When the tea is ready, let the brew sit until the compost is pretty much settled out, which is usually 10 to 20 minutes.  Then strain it into another bucket or directly into the sprayer.  If desired, this is the time to add foliar micronutrients, like kelp, molasses, humic and/or fulvic acids, commercially available microbial spore suspension, or rock dust.  These stimulatory additives can be included to improve the final quality of the compost tea.  Once the aerators are shut off, use the tea within the hour if possible.  The solids left over after the tea is finished can be returned to the compost pile or added to the soil.

 

Spraying can be done as little as one time in the spring up to every two weeks during the growing season.  Compost tea can be applied as a foliar spray.  For best results, at least 75% of the upper and lower leaf surface should be covered with each application and should be applied every two weeks though out the growing season.  As a soil drench, the tea should be applied at about 1 quart per plant.  Start when the plants have developed their first set of true leaves.  On trees and shrubs spray two weeks before bud break, then every 10 to 14 days.  The tea should be applied before 10:00AM or after 3:00Pm on sunny days because the UV light will kill the microorganisms.

 

Odor

With any form of compost, solid or tea, bad smell means bad product or anaerobic compost.  Healthy, adequately oxygenated compost and compost tea should smell sweet and earthy.  Never use a smelly compost tea on your plants.  The problem is that alcohol from the anaerobic decomposition destroys cell walls and plant roots.  If the compost tea smells bad aerate it until the smell goes away.

 

Microorganism Selection

Compost tea can be dominated by either bacteria or by fungi. Bacteria dominated compost tea is for use as a foliar spray applied to herbaceous plants.  It is especially useful for preventing foliar diseases.  For the bacteria to dominate, it should be made from a preponderance of green materials such as 25% high nitrogen ingredients, 45% green plants, and 30% woody material.  High nitrogen materials include manure, grass clippings, and legumes such as alfalfa, peas, clover, and bean plant residues.  Green material includes any green plant debris, kitchen scraps, and coffee grounds, which all contain sugars and proteins that bacteria love.  Woody material includes wood chips, sawdust, and paper products.  The more frequently you turn the pile, the more the compost tends to become bacterial.

 

Fungi dominated compost is good for mulching around berries, fruits, and trees.  Fungal compost consists of approximately 25% animal manure, 50% green plant material, and 25% shredded wood plant material.  Any kind of disturbance to the compost pile destroys fungi by breaking up the mycelia.  Fungal compost is especially useful for suppressing disease and introducing fungi for root development immediately after tree planting.

 

If worm compost (vermicompost) is used, the material does not have to reach the same temperatures but must be adequately processed by the worms. Passage through the earthworm digestive system kills human pathogens and most plant pathogens, but adequate time must be allowed for worms to process all the starting materials.

 

Sources

·         Hingham, Elaine R., “Brewing Compost Tea”, Kitchen Gardener – October/November 2000, No. 29

·         Martens, Mary-Howell R., “Just What the Doctor Ordered”, Acres USA, February 2001

·         Soil Foodweb Inc. website, http://www.soilfoodweb.com