How to Make Compost Tea

Chemical-based, synthetic fertilizers and pesticides kill microbial life in the soil. It is these beneficial microbes and fungi that help plants develop strong root systems by making it easier for plants to take nutrients from the soil. Organic gardeners have always depended on compost for supporting these beneficial microorganisms and fungi, thereby enriching their soil and providing nutrients for plant growth.

Compost tea takes the composting process one step further. It is made by steeping fully mature compost in water to draw out the nutrients. Making tea from compost only increases its usefulness. Compost tea increases the nutrients and minerals available to your plants and improves soil structure. It also suppresses diseases when used in a foliar spray.

Making a Simple Compost Tea Brewer

You will need two five-gallon buckets, an aquarium pump large enough to support three air stones, twelve feet or so of tubing, three air stones, and a gang valve. A gang valve is a plastic splitter, designed to take one air tube – from the pump – and split it into two or more outlets – in this case, three. You will also need a stick for stirring the mixture, an old pillowcase, and some organic unsulfured molasses. Sulfur dioxide is a preservative, but can have negative effects on microorganisms.

Compost tea must be aerated to prevent the growth of organisms that use all of the available oxygen. Without aeration, the tea becomes anaerobic and starts to smell. Anaerobic organisms produce alcohol that can do harm to your plants.

Attach one end of a piece of tubing to the pump, the other end to the gang valve. Cut three equal length pieces of tubing. Attach one end of each to the gang valve and place an air stone on the other end.

Add a healthy shovel full of loose compost to the bucket. Place the air stones, equally spaced, in the bottom of the bucket under the compost. Fill the bucket with water – three inches from the top – and start the pump. While the pump is running, measure out and add about an ounce of molasses to the mixture and stir vigorously. Your tea is now brewing. Stir a couple of times each day for two to three days.

It is important to use clean, non-chlorinated water. Chlorinated water will kill the beneficial microorganisms that you are trying to grow. Rainwater is your best option, but you can use distilled water or water directly from a well. If your only option is chlorinated water, you can aerate it for an hour or two to disperse any chlorine.

For large gardens, several ‘compost tea brewers’ can be found on the Internet. Be sure to inquire about brewing times and oxygen concentration during that time. Oxygen levels should not fall below 15% to total atmospheric gasses.

Using Compost Tea

Once the tea has brewed for three days, remove the pump and let the solids settle to the bottom of the bucket. Then use your old pillowcase to strain the tea into the second bucket. You should have 2 ½ – 3 gallons of compost tea. The leftover solids can be spread over the planting beds or tossed back into the compost pile.

Aerated compost tea contains living microorganisms, so use it immediately. As a mild fertilizer, simply apply to the soil around your plants. Add powdered seaweed or fish emulsion to the tea for a well-balanced fertilizer.

Spraying your plants with compost tea inoculates them with microorganisms that keep diseases from developing. For disease control, spray your plants as often as every two weeks. Once a month is usually sufficient unless your garden lacks a healthy insect population. Spraying your planting beds immediately prior to planting helps prevent damping-off of seedlings.

A Note About Compost

Unfinished compost may harbor harmful pathogens. So it is important to use matured, high-quality compost. Quality compost ingredients include leaves, fruit and vegetable scraps, coffee grounds, egg shells, untreated grass clippings, manure from herbivores – cows, horses, poultry– paper and cardboard.   It’s a good idea to cover your compost pile to prevent nutrients from leaching during rain events. Compost may take anywhere from four weeks to six months to mature, depending on how intensely you manage it.

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