taken from Maximum Yeild INTRODUCTION You’ve seen the ads, you’ve read the hype, but what exactly is compost tea? Is it the next best thing in growing technology or just another passing fad? More important, how do you make it and what can it do for you? Although it is increasingly accepted by the organic growing community, there are still questions as to the benefits of using compost tea in hydroponic systems. “Teas” made by soaking manure, compost, or worm castings in water have been around for hundreds of years. The resulting nutrient-rich mixture is, in fact, not compost tea but more accurately compost extract or leachate. Products on the retail shelves called “plant teas” are very similar. While these products can be beneficial, modern aerated compost tea is a more recent discovery, with potential to change your whole idea about cultivation. WHAT IS COMPOST TEA? Aerated compost tea looks like a murky brown liquid (sometimes foamy on top) that has a rich, earthy, somewhat sweet smell. This liquid is alive, teeming with trillions of micro-organisms, with a rich diversity of thousands of kinds of bacteria and fungi. The secret to all this life is the brewing process: air is forced through a mixture of high-quality compost and complex microbial foods suspended in water. The oxygen and nutrients produce an extraordinary explosive growth of bacteria and fungi. Consider that a teaspoon of good compost contains a billion or more bacteria. Given the right environment, those bacteria can double in population every 20 minutes. In the normal brewing period of 1248 hours, those microbes turn into countless numbers of beneficial organisms. Added to soil or a hydroponic solution, the microbes quickly go to work, converting everything around them into food for plants. COMPOST TEA INGREDIENTS Compost Starter The quality of compost tea depends on its basic ingredient the compost or source of microbial life. Like the “starter” used in yogurt, everything depends on the micro-organisms it contains. The USDA has warned compost tea makers of the possibility of contamination by Salmonella and E-coli found in some commercial manures and composts. It is essential to use only the highest-quality organic non-manure, unpasteurized compost to make tea. Experienced growers build their own compost piles that heat up from biological activity. The resulting dark brown substance is a nursery for beneficial organisms and is good for compost tea. Most compost tea makers reach for vermicompost or worm castings. These are easily available and have high levels of bacteria. Obtain them from a reputable organic supplier, because their effectiveness depends on the species of worm and the kind of food they have been fed. One drawback is that worm castings may not have the necessary diversity of fungal spores. COMPOST TEA TIME FOR GROWERS Gaining popularity with compost tea makers is a fine-grained humus that comes from Alaska. This is marketed under a number of different names: Alaska Humisoil, Alaska Humus, or Alaskan Magic. Extensively tested by independent laboratories, this humus has been found to harbor an extraordinary diversity of both bacteria and fungi, and it is naturally free of pollutants and pathogens. Aerated Water To make tea, the starter compost is added to pure, aerated water. High levels of chlorine in the water may kill off the microbes, so it is important to aerate the water for a couple of hours to allow chlorine to off-gas. The dissolved oxygen level must be kept high to nourish the aerobic microbes. Many efficient aeration or brewing systems are now available. You can make your own using an air pump and a bubbling system. A double-outlet aquarium pump with a bubbler, to produce tiny micro-bubbles and gently agitate the tea, is sufficient air to brew a 5-gal. bucket. Brewing the tea is as much an art as a science; treat the tea like a living organism. Insufficiently aerated compost tea may go anaerobic, which is poisonous to plant roots. This is easy to determine because the tea gives off a sour smell. Leave the tea for more than six hours without aeration and it dies from lack of food and air. Microbial Foods Microbes are hungry. Like every living thing, they need to be fed. The art of compost tea brewing is knowing how much and what nutrients to add to make the kind of tea you need. Bacteria feed on simple sugars, easily available in the form of non-sulfured molasses. Nutrients such as fish protein support both bacteria and fungi. Kelp, humic acid, and fibrous materials such as oat bran are good fungal foods. Brewing at shorter, higher temperatures of 75ºF85ºF, tends to produce a quick bloom of bacteria. Brewing longer at lower temperatures of 60ºF75ºF gives the fungi a chance to flourish. Why the concern for bacteria and fungi? Fast-growing leafy plants prefer a more bacterially dominated environment for their roots, while woody-stemmed plants like it more fungal. If you want to grow greens or annuals, then brew for bacteria. If tomatoes, shrubs, or trees are what you are looking for, go more fungal. In general, a balanced bacterial/fungal tea will produce great results across the board. If you are unsure whether your tea has the optimum diversity of microbes, send it to a reputable lab for testing (see www.soilfoodweb.com). WHY USE COMPOST TEA? Making compost tea may sound a bit complicated, but the results can be extraordinary and the ideas behind it make intuitive sense. Plants and soil life have grown up together, co-evolved over millions of years. The countless organisms in healthy soil bacteria, fungi, protozoa, nematodes, arthropods, earthworms, and plant roots form a living ecology called the “soil food web.” Prey and predator, catalyst and symbiote are interlocking parts of the great web of life. The underpinnings of this ecology are the microbes and their relationship with roots. Many microbes are drawn to plant roots, which feed them tiny drops of sap. In exchange these criters break down minerals into easily digestible forms and fix nitrogen from the air. Not only are microbes food for other important members of the soil-food web, but their dead bodies are super plant nutrition. Plants prefer their food biologically pre-digested, just as we prefer our food cooked. On this diet they naturally grow stronger and healthier. COMPOST TEA AND SOIL Organic growers have been using aerated compost teas for about 20 years. The positive stories are many and the scientific evidence is growing steadily. Research results, while somewhat confusing, suggest that aerated compost tea enhances soil fertility, growing bigger, stronger plants with larger yields. Just as important, foliar spraying with tea can help control a number of plant diseases (see “The Secrets of Foliar Spraying,” Maximum Yield, July/August 2007). Tomato plants treated with compost tea are stronger and resist blight better; turf roots grow more vigorously; grape, banana, and avocado have higher production and less disease; seedlings show less damping off; leuce and greens produce faster growth. An important two-year research program by the Rodale Institute and Penn State University conclusively showed that aerated compost tea reduced powdery mildew on grapes by 50 percent and increased potato yields by 19 percent. Those potatoes had an extremely high mineral content. More anecdotally, committed tea users say that the microbes in compost tea help break up impacted soils, clean up toxic chemicals, and greatly cut down on the need for added fertilizers. Some results are remarkable: John Evans, winner of numerous Guinness World Records for giant vegetables, used only compost tea to grow his 19-lb. carrot and 75-lb. Swiss chard.