Brew Your Own Microbial Compost Tea

The idea

Compost tea is a liquid form of compost, packed with beneficial microorganisms that enhance soil and plant health. The goal is to extract these microbes from solid compost into water and then provide them with food to multiply, creating a concentrated microbial solution.

To make a 5-gallon batch of compost tea, you will need:

• A 5-gallon bucket or similar container.
• A brew bag (a paint strainer bag works well).
• An air pump (rated at least 1 liter per minute per gallon of water, so 5 liters per minute for a 5-gallon bucket).
• Air hoses to reach the bottom of the bucket.
• Weights to keep the hoses submerged (like old forks or nuts).
• 2-3 cups of high-quality vermicompost (worm castings) or 3-5 cups of regular finished compost.
• Microbial foods: 1 tablespoon of humic acid, 1 tablespoon of fish hydrolysate (not fish emulsion), and 1 tablespoon of soluble kelp (powder or liquid). If you don't have one of these, you can use the others.

Steps:

1. Fill your 5-gallon bucket with non-chlorinated water. Well water or rainwater is ideal. If using tap water, let it sit uncovered for 24 hours or aerate it with the air pump for 12 hours to off-gas chlorine. Humic acid can also help tie up chlorine ions.
2. Place the compost into the brew bag.
3. Submerge the brew bag in the water.
4. Massage and squeeze the compost within the bag to break down aggregates and release microorganisms and organic matter into the water. Work the compost between your fingers and against the sides of the bag.
5. Add the microbial foods (humic acid, fish hydrolysate, soluble kelp) to the water. You can add them before or after massaging the compost.
6. Place the weighted air hoses into the bucket, ensuring they reach the bottom to aerate the entire water column.
7. Turn on the air pump and allow the mixture to brew. The brewing time will depend on the ambient temperature.

Why it works

Compost tea works by introducing a diverse population of beneficial bacteria, fungi, protozoa, and nematodes directly to your plants and soil. These microorganisms play crucial roles in the soil food web:

• Nutrient Cycling: They break down organic matter, making nutrients available to plants in a form they can easily absorb.
• Disease Suppression: Beneficial microbes outcompete and suppress harmful pathogens, protecting plants from diseases.
• Improved Soil Structure: Fungi and bacteria create soil aggregates, which improve water infiltration, aeration, and root growth.
• Enhanced Plant Growth: A healthy microbial community supports stronger root systems and overall plant vigor.

By providing specific foods like kelp, humic acid, and fish hydrolysate, you encourage the rapid reproduction of these beneficial microbes, particularly fungi, creating a highly potent solution. Aeration during brewing ensures an aerobic environment, which favors beneficial microbes and prevents the growth of harmful anaerobic organisms.

Try it

1. Gather materials: Find a clean 5-gallon bucket, a reusable mesh bag (like a paint strainer), an aquarium air pump (check for a rating of at least 5 liters per minute), air hoses, and some weights.
2. Prepare water: Fill the bucket with rainwater or well water. If using tap water, let it sit in the sun for a day or aerate it with the pump for 12 hours to remove chlorine.
3. Add compost: Place 3-5 cups of high-quality compost (or 2-3 cups of vermicompost) into the brew bag and submerge it in the water.
4. Massage: Squeeze and massage the compost in the bag for about 3 minutes to release microbes and organic matter.
5. Add food: Stir in 1 tablespoon each of humic acid, fish hydrolysate, and soluble kelp.
6. Aerate: Place the weighted air hoses into the bucket, ensuring they reach the bottom, and turn on the air pump.
7. Brew: Allow the mixture to brew. For optimal results, brew at the same ambient temperature at which you plan to apply it. The tea is ready when the microbial population peaks (typically 12-24 hours depending on temperature).
8. Apply: Filter the compost tea through a second filter if using a sprayer or drip emitter. Apply the tea to your plants and soil, aiming for 10-20 gallons per acre for larger areas, or simply enough to cover your plants for smaller gardens. Repeat once a month.

Watch out for

• Chlorine: Always use non-chlorinated water, as chlorine can kill beneficial microorganisms. Allow tap water to sit or aerate to remove it.
• Airstones: Avoid using porous airstones with your air pump, as they can clog with sticky microbial foods and develop undesirable biofilms that are hard to clean.
• Temperature: Brew and apply the compost tea at similar ambient temperatures to ensure the active microbes are adapted to the environment they'll be introduced to.
• Fish Emulsion: Use fish hydrolysate, not fish emulsion. Fish emulsion has oils and fats removed, which are important food sources for beneficial fungi.