Tech Talk No. 124
Looking for an inexpensive way to improve plant growth? Try compost tea. Compost tea is exactly what it sounds like—a liquid extract prepared by steeping compost in water. Sounds delicious, right? Don't worry, it's for your plants. Just spray it on and watch them grow healthier and less susceptible to disease. Compost tea can be used on trees, shrubs, houseplants, vegetables, flowers and lawns. It can also help with seed germination and starting new plants.
Compost tea has been shown to be a source of beneficial microorganisms that protect plants and provide better nutrient availability to the plants while also improving soil condition. Several types of compost teas can be made, and they vary in the method of preparation and in the ways they are used. Examples include anaerobic compost teas, aerobic compost tea, compost leachate, manure tea and Bokashi tea, among others.
One of the most popular of the compost teas is aerobic compost tea (no, it has nothing to do with jumping jacks). Aerobic compost tea is made by using an air pump or blower to supply your mixture with oxygen while brewing. The process enhances the production of beneficial bacteria, protozoa, fungi and other microbes. You can even add food and/or other additives to further encourage the growth of microorganisms in the tea. For example, add molasses for bacteria growth; kelp and humic acid for fungi; and peat moss and hay for protozoa.
Brewing aerobic compost tea is easy. Many commercial compost tea brewers are available, but if you take pride in your DIY ethic you can easily build your own brewer. All you need is a bucket, an air pump or blower, an air hose with check valve and a diffuser. Simply wrap the compost in cheesecloth or place it in a mesh bag (avoid fine mesh—it may keep some beneficial fungi from the tea). Fill a bucket with clean water (one part compost to four parts water) and drop the bag in. Then throw in your choice of additives. Aerate the liquid for several hours.
While it brews, make sure you provide enough aeration to maintain dissolved oxygen (D.O.) content around 6 ppm. This will support the growth of aerobic microorganisms that enhance plant growth. Aerate the extract between 12 and 48 hours, depending on the type of microbes that are desired. A period of around 12 hours will favor the growth of fungi, while a 24-hour period of aeration will favor the growth of bacteria. Longer periods (36–48 hours) will favor the growth of protozoa and other microorganisms.
After aerating, pour the liquid through a strainer or cheesecloth to filter. Then dilute the concentrated tea with clean water at a ratio of 1 to 10 before dispensing in sprayers or spray bottles. One gallon of your diluted mixture will cover 800 ft2 of planted area. For best results, apply the tea to plants and soil once every week. The whole plant and surrounding soil may be thoroughly wetted. Tea may be stored up to two weeks in a closed container before applying to plants.
To consistently make great compost tea, consider the following:
• Aerate or chemically treat clean water to remove chlorine or chloramines from water prior to adding compost.
• Keep the brewer between 70 and 75°F while brewing tea.
• The pH should be near neutral (6.5 to 7.5).
• Maintain the D.O. concentration around 6 ppm throughout the brewing cycle.
Using these methods, you can routinely make tea with high numbers of beneficial bacteria, fungi, protozoa and nematodes, time after time. The result will ensure healthier plants and better growth.
Sources of additional information on compost tea:
ATTRA website: http://www.attra.org/attra-pub/compost-tea-notes.html
The Compost Tea Brewing Manual, 5th Ed., 2005. Dr. Elaine Ingham, Soil Foodweb Inc., Corvallis, Oregon 97333.
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