Compost Tea

Compost tea, very simply, is a cold brew water extract of compost. While most people understand that it is microorganisms that breakdown organic material into nutrient heavy compost, many don't understand that the microorganisms continue to be productive and valuable. By steeping compost in properly aerated and dechlorinated water, you can transfer beneficial microorganisms from compost into soil and onto plants. It is a cheap, highly effective way of establishing and reinforcing a healthy food web in soil and on plants that poses none of the risks associated with synthetic chemical fertilizers.

The most essential ingredient in compost tea is, naturally enough, good compost. You can refer to our previous post to learn the basics of compost. Making your own is advisable but it can be purchased as well from a reliable source to ensure that it is both pathogen free and contains the necessary soil food web biology: beneficial bacteria, fungi, nematodes, protozoa, and microarthopods.

The next necessary ingredient is clean water. Water from a septic tank or public utility is fine so long as time is allowed for it to dechlorinate. Chlorine kills the microorganisms that we are trying to cultivate, but thankfully it is unstable in water and will evaporate if left out in the open for 24 hours or so. Chlorine filters for taps and hoses are also commercially available. Since we steep our tea outside we make sure its covered to protect it from the sun's heat an UV rays that kill microorganisms. Application before noon helps avoid this as well.

How long the compost needs to steep depends on various factors (multiple recipes for multiple results are available in books and elsewhere on line), but the process always needs to be thoroughly aerated. There are custom-made tea brewers on the market, but an aquarium pump in a five gallon bucket works fine. Some people opt for a “loose tea” approach and put the compost directly in the water but we put it in “tea bags” made out of nylon stockings. This helps filter out particulate matter that might otherwise clog up the sprayer that we use for foliar application.

A few things happen when you spray of compost tea directly onto the leaves. The water acts as a “carrier” for the microorganisms in the tea and are delivered to leaf surfaces where the beneficial organisms consume the surface exudates, leaving no food for disease-causing organisms. The water also allows organisms to be absorbed through the phyllosphere and through the stomata (tiny mouths on the underside of the leaf through which the plant respirates), translocating through the vascular system of the plant.

Compost tea can also be applied directly to the soil as a “drench.” From what we've read, some growers believe that soil applicant has more benefits and recommend using compost tea as a foliar feeding only when absolutely necessary – when a crop seems to be displaying symptoms of a disease, infestation or malnutrition of some kind. Foliar feeding also seems to greatly benefit young plants during critical periods of their development. Since we are on a farm with lots of young trees (mostly coffee), we spray tea directly on to the leaves once a week as a part of the ecological management strategy. We drench the soil of the older trees (mostly macadamia), whose leaves are largely too high to reach anyway, taking care not to spray the bark. The microbes will start feeding on it. You want them as partners, not parasites.

Trees prefer their nitrogen in ammonium form as opposed to nitrate so we brew a tea heavy in fungi to encourage ammonium production in the soil food web. To encourage fungi we supplement with guano, kelp, and select minerals during the brewing process.

Compost tea made from good compost expeditiously improves the life in the soil and on plant surfaces. The introduction of these organisms into your garden/farm helps achieve higher microbial biomass, better plant production, better soil structure, better nutrient cycling and less disease. Decomposition of plant materials improves. There's no dangerous chemicals to leech into the groundwater but if there were they would be reduced because of improved water retention in the soil. You can't over apply it; excess microorganisms will simply die off.

Not only safer for the soil and plants, it's more healthy for us, too. Sometimes the fishy smell makes us think masks might not be a bad idea but it's totally safe to breath---unlike the stuff C's brother P sprayed working for a certain chemical spraying company. Jumpsuits might be cool, too. The backpacks make us feel like Ghostbusters.