The concepts of living soil and a soil food web are an approach to gardening and growing food that considers soil as a living ecosystem. Healthy soil has organic matter, nutrients and a balance of beneficial and predatory organisms, fungi and bacteria. When we pay attention to this as a vital system, we get better results with harvests and a more resilient landscape.
Monique Bosch is the soil health program manager with the Connecticut chapter of the Northeast Organic Farming Association. I studied with her last year while completing its Organic Land Care course. She wrote the regulations about vermicomposting and compost tea, and has researched and practiced both for years.
How is compost tea distinct from other forms of compost?
Composting is the breakdown of organic matter with the help of microbes by heating it to a certain point. In a thermophilic process, it has to reach 131 degrees for 15 days. That’s what you get when you buy it at the store. To achieve this, you need a balanced carbon/nitrogen ratio mixed in the right proportion. The temperature kills pathogens and if it’s heated to 143 degrees, then weed seeds will die.
In vermicomposting, worms do the work. The advantage is that you’re not killing the “good guys” — the predator microbes and fungi — with heat.
With compost tea, you’re taking the microbes and giving them a food source to multiply. Then you can apply it directly onto the plant. It’s aerated — you need oxygen — and the goal is to multiply the microbes.
So what’s the difference between compost tea and compost extract?
The process is different. If you have worm castings or compost and put them in a bucket of water and stir it, the microbes will be extracted and you can feed plants with it. It still works as a fertilizer, but you’re extracting the microbes rather than feeding them and multiplying them.
Why would a gardener want to use compost tea?
Of all the methods we’ve covered, it’s the most effective. The plant can immediately take it up. The microbes feed the plant sugars and the plant feeds on the nutrients. It improves water retention and plants need less water. With that immediate hit of nutrients, plants can resist pathogens more quickly. Plant roots have been found to grow deeper and decomposition of organic matter speeds up.
I’ve also used it treat downy and powdery mildew, rust and other fungal diseases. Spray it on the foliage and microbes feed on the bacteria. If you get rid of it and it’s humid again, it might come back. But many times a single application is all I need.
How can gardeners make compost tea?
You’ll need a 5-gallon bucket that is washed with hydrogen peroxide to remove any biofilm. An aquarium pump will aerate the mixture and can be held down with a rock. Tap water is fine. Add 1.2 teaspoons of fish hydrolysate (food for fungi), 1.6 tablespoons of kelp (food for bacteria and fungi) and 1 tablespoon of humic acid (it acts as a binder) to the water.
You can use compost, worm castings or soil from around a healthy tree. Put 2 cups in a 400-micron mesh bag (available as a paint strainer) or cheesecloth and submerge it in the bucket with the pump running for 24 hours. The microbes will multiply by the billions.
What is important to know about using compost tea?
It can go anaerobic quickly. Use it immediately after brewing for 24 hours. Don’t let it sit in the sun. I look at it under a microscope and can see the microbial activity and know when it’s gone anaerobic and the microbes are dead. Without a microscope, just use it right away and don’t let it sit around.
It can be sprayed on foliage or used as root drench. It’s most effective to apply it at sunset and then the dew comes out to coat the leaves and it will last longer. Don’t use it when it’s hot and sunny. It can burn the leaves.
While it’s good for any stage of growth, compost tea helps the most when plants are going through a major output of energy. When you’re potting up seedlings, dip the roots in tea and the microbes will go right into the soil around the roots.
Can it ever be overused?
Not really. The plants will only take up the nutrients they can use.
For more information about the soil food web, Bosch recommends microbiologist Elaine Ingham’s work and a course she teaches. See soilfoodweb.com.
