COLUMNS Part I: What is it, how to make it, how to use it
Organics
Compost Tea
Compost tea is essentially a water-based compost extract. Much like a tea bag is steeped in water for its beneficial properties, compost is steeped in water and minute microbes, particulate organic matter and water-soluble chemical molecules filter out of the solids and into the water. By transferring these from a solid form to a liquid form, you can expand your farm’s tool kit with respect to disease control and soil fertility management. When compost tea is sprayed on a plant, stomata on the stem, leaves and flowers absorb its nutrients, and the tea’s large and diverse community of microbes can potentially inhibit the growth of pathogenic organisms by competing for space and food. When soil surrounding a plant is drenched with compost tea, the nutrients are readily absorbed by the roots, and the microbes boost the number and diversity of soil microorganisms, which in turn boosts the soil’s ability to retain and release nutrients, hold water and assist with disease resistance.
Whipping up a batch of compost tea is much like making a loaf of bread: the basic ingredients to make a dough are water, flour, yeast and salt, but their proportions and the amount of time that dough is allowed to rise and bake varies from farm to farm. The two basic ingredients that dominate a compost tea recipe are, not surprisingly, water and compost, but their ratio varies according not only to personal preference, but also to the amount of energy you want to put into the process. You can aerate your compost tea by injecting air into the water as it steeps or by recirculating the water for 24 hours. The benefit of aeration is you’re providing aerobic levels of dissolved oxygen to the microbial community, allowing it to expand and grow. Why do you want it to grow? The larger and more diverse the community, the more likely it is to aid in the fight against disease.
If you’re going to aerate, fill a mesh or burlap bag with one part compost, immerse it in a container and add 10 to 50 parts water. You can purchase commercial tea brewers that are ready and waiting to aerate when you pull them out of the box, or you can rely on your Yankee ingenuity and design a system using such items as your kid’s old fish tank and bubbler or a sump pump. After only 24 hours, the aerated tea is ready.
If you don’t want to go through the bother of aeration, another option is to produce non-aerated compost tea. This requires the least amount of energy to produce, but the tea will need to steep for a longer period of time. The compost-to-water ratio is one part compost to three to 10 parts water. Put the compost in a bucket with holes, mesh bag or burlap sack and let it set in the water for a few weeks. Some like to occasionally stir the concoction, others simply let it be. At the end of your setting period, filter it to avoid plugging you’re watering can, sprayer or irrigating unit. Five gallons of your freshly brewed tea, be it aerated or non-aerated, is enough to cover an acre of cropland. Another way to think of it is a pint for every 1,000 square feet. If you’re drenching your soil with it, do so two to three times during the growing season. If you’re spraying it on your plants, do so every 10 days.
Back to the bread analogy. Just as some bread makers may add, for example, an egg, oil, oatmeal or sunflower seeds to the dough to jazz it up, so may a farmer add something other then water and compost to his compost tea concoction. Over time, brewers have learned that adding certain nutrients to the solution will increase the overall biomass of microbes in the tea. Molasses, yeast extracts, algal powders, products derived from fish and soluble kelp, when added to the mix, have been shown to significantly increase the number of microorganisms. These additives are best for aerated tea production. Too many nutrients in a non-aerated system will produce a less oxygenated, anaerobic solution that stifles the microbial community you’re trying to support. Also, substances like phenols and alcohol could be produced and harm your plants. For a passively aerated system, stick with the compost and avoid adding other nutrients or fertilizers to the mix.
Many growers who apply compost tea to their crops observe an increase in plant vigor, growth and yield, as well as a decrease in the incidence of foliar diseases and root rot. Although the amount of anecdotal evidence is piling up, the science behind this phenomenon is just now being investigated. We do know that, just as the nutrient content of compost varies from farm to farm, so does the nutrient content of compost tea. Compost teas also vary in their ability to fight disease, and that may be tied to what originally went into the compost and how long it was composted for. If you’re serious about the use of compost tea and want to know your tea’s nutrient or biological profile, there are labs that will analyze it for you. For folks in the Northeast, Woods End Research Laboratory, Inc. in Mt. Vernon, Maine is a good place to turn to. They can, among other things, determine whether pathogens and beneficial microbes are present in your compost tea. Call them at 207-293-2457 or visit their Web site at www.woodsend.org to learn more about the process.
As the number of organic growers has increased, so has the demand for effective ways to manage pest and disease outbreaks and soil fertility. Interest has grown in compost tea, but so has the concern that it could be an avenue for not only propagating beneficial microorganisms, but also pathogenic bacteria (i.e., E. coli) that could potentially contaminate crops. In response to this concern, the National Organic Standards Board assembled a compost tea task force in 2003 to review the literature and recommend reasonable uses for compost tea. Next month I’ll write about that review, its findings and what that means for the certified organic grower.
The author, a brand-new contributor to Farming, is a biologist who lives and farms in Vermont’s Northeast Kingdom. Comment or question? Visit www.farmingforumsite.com and join in the discussions.