By Levi Glenn
A few years back we started to make and apply compost tea in the vineyard. It was an effort to try to improve our soil, a central theme in organic farming: improve the soil and the plant will follow. Compost tea contains two important soil improving components: nutrition and soil microbes. Microbes are microorganisms that help us in many ways, but most notably by breaking down organic matter (slowly decaying carbon compounds) into yet smaller particles and ones that plants can readily consume. You could see it as basically freeing up nutrition that already exists in the soil. It’s a process that isn’t completely understood, but is definitely going on below our feet. Amazingly, there are an estimated 500 billion microbes in one pound of soil. Yes, that’s billions with a B. What I’m describing is just the one part of the soil food web, one where microbes, worms, nutrients, plants and animals all interact. The more of this life we have in our soil, the healthier the plants that grow in this soil should be. A diagram below (found in the soils section of the USDA's Web site) illustrates:
The complex (and only somewhat understood) interactions in living soil are the main reason why modern chemical farming practices tend to be counterproductive over the long term. Synthetic herbicides kill the weeds above ground, but their effects are farther reaching than this: they also kill off the microbes as well as impacting the food supply for the worms and insects that create a living, vibrant soil belowground. Chemical pesticides have similarly profound impacts underground. That’s at the heart of why we farm organically.
In addition to the microbial component of compost tea, additional benefits include increased growth through improved nutrition, better soil structure, and disease suppression. The tea can be sprayed on the leaves as a foliar fertilizer, or applied directly into the soil through our irrigation lines and drips. One function we’ve been particularly intrigued by is compost tea’s ability to suppress powdery mildew. Spraying compost tea on our grapevines has allowed us to significantly reduce the amount of sulfur we use as a natural fungicide.
We’ve been making compost tea for years, using a simple system we built ourselves (right). We would then use the tea in two ways. We would load the brewed tea into sprayers and apply it directly to the leaves to inhibit mildew, and we would run it through our irrigation lines to build up our soils. This year we took the plunge and bought a 500-gallon commercial compost tea brewer (below).
Brewing takes roughly 24 hours to complete. We start with worm castings, compost and fish bonemeal powder. Worm castings (below, left) are a fancy term for worm dung, a highly refined source of nutrition. The compost we’re using (below, middle) is made on the property out of our vine prunings, green waste and manure. The fish bone meal (below, right) provides a much needed source of phosphorous in the vineyard and is an additional food source for the microbes in the brewing process.
These three ingredients are put into a wire mesh cylinder (below, left), which is placed into water to steep. Below each cylinder are powerful bubbling aerators (below, right) that help to saturate the mixture and provide oxygen to the microbes. There are also smaller aerators that go inside the cylinders to further promote an aerobic environment.
Before the brewing, the bacteria, fungi, and protozoa in the “tea” are in somewhat of a dormant state. By creating the right environment for these microorganisms by adding water and oxygen to their environment, keeping them at an optimal temperature, and providing an accessible food source, their numbers grow exponentially during the brewing process.
When we’re done, we have 500 gallons of what looks like a weak batch of coffee, but is actually a microbe-rich elixir, a liquid soil of sorts. And no, you wouldn't want to drink it, any more than you would want to chew on our soil:
When we brew a new batch, if we’re curious what’s in it, we can send a sample off to the lab. The analysis the lab runs shows us the total number of bacteria and fungi in the tea, and the proportion between the two. Some plants prefer a higher concentration of bacteria in the tea, like vegetable crops, where as vines and trees do better with a fugal dominated tea. After a few trial batches we’ve been getting consistently good lab results and are confident in our process.
While there is often notable benefit from even short-term compost tea use, we hope that longer-term use will provide exponentially greater benefit. Our principal vineyard challenge is Paso Robles’ harsh vineyard environment: the same thing that makes the grapes we grow such good raw materials for winemaking. Paso Robles is so dry and sunny in the summer, so cold in the winter, and has such a great diurnal swing in temperature year-round. Plus, our topsoil is relatively thin and rocky. It’s not easy maintaining the health of our vineyards in this climate, and doing so is the reasoning behind almost every decision we make in the field. Applying compost tea at significant volumes, over a matter of years, should help our grapevines to continue to flourish even as the neighbors who are farming more conventionally have to replant because their vines are exhausted.
So now we’re farming wine grapes, olives, sheep, and microbes. I can’t wait to see what we’ll be growing in the future.