Organic Growing Techniques

How Do I Brew My Own Compost Tea at Home?

Evan Folds from Progress Earth, the maker of the Vortex Compost Tea brewing system, takes us through the process from start to finish.

You may have already read about “beneficial biology” and "compost tea." But what exactly is it? Furthermore, how do we get hold of this "beneficial biology" and actually utilize it in our gardens? 

Microbes are responsible for aiding limitless plant processes, including helping plants feed, protecting them from disease and creating the very soil that serves to support us all! 

Microbes work in partnership with plants. They break down organic matter (which is inaccessible to plants) into a form that plants can use. Think of them as little ‘compost conversion’ factories!

It’s incredibly easy to breed these microbes at home! It’s called “actively aerated compost tea” or AACT for short. Think of it as “life juice” for your plants—a brown soup that’s full of the sort of beneficial microbiology you find in healthy soil—the essential components of any organic growing situation!

Compost Tea and the Soil Food Web

Microbes and plants are natural teammates, so compost tea is a great way to replenish and enhance this wonderful relationship. It can get fairly complicated though and our current understanding is “rule of thumb” at best. No living organism operates autonomously. In other words, there is a symbiosis, or “give and take,” found in the natural world that we humans take for granted, and therefore restrict.

All microbes operate by way of teammates. They play off of each other, with one teammate unlocking the ability of the next.

How To Make Your Own Actively Aerated Compost Tea

Humus is fully composted organic matter.You start with humus! Humus is organic matter that has gone through a full composting process. Think of it like “compost” that cannot be “composted” any more! Microorganisms are found dormant in quality humus sources like worm castings, but can be awakened and stimulated to grow under the right conditions.

Compost tea is the result of adding a humus source to (non-chlorinated) water and using air pumps to increase the amount of air in the water solution in order to grow microbes. Finally, you need to add some sort of food and catalysts for the microbes to grow, such as molasses, kelp, rock dust, fish, humate, or sea minerals.

DIY Compost Tea

  • Ready-to-go compost tea brewers are available at your local grow store. Alternatively you can make one yourself. Here’s your shopping list:
  • An aquarium pump large enough to run three bubblers or air stones
  • Several feet of tubing
  • A gang valve
  • Three bubblers
  • A porous bag for the compost, like a nylon stocking OR Something to strain the final tea, like an old pillowcase or tea towel.
  • A bucket

The above list shouldn’t set you back more than $65. Compost tea takes just 12 – 24 hours to brew. A little foaming on the surface is a good sign that your compost tea (or rather the microbial life within) is flourishing.

Compost tea brewing in a Vortex Brewer.The higher the water temperature the greater the biological growth, but the lower the dissolved oxygen. Dissolved oxygen levels above 6 parts per million (ppm) will provide sufficient biological growth, and levels around 8 ppm are attainable at room temperature. An accepted approach among compost tea enthusiasts is to brew AACT at a similar temperature to where it’s being used, for example; if your root zone temperature is 68°F (20°C), brew the AACT around this temperature.

The food source utilized when brewing compost tea can determine the microbe grown. Thus you can adapt the ingredients you use to brew compost teas to your particular crop. For instance, a sugar source like molasses fed to a balanced stable compost inoculant will encourage more bacterial growth, whereas kelp or fish fed to the same inoculant will encourage more fungal growth. The same is true for other inputs, like Equisetum (horsetail), which encourages the growth of beneficial nematodes. To be clear, molasses do not discourage fungi from growing, they simply encourages bacteria more. Similarly, using a fungal dominant tea on an annual plant will not harm it in any way; it’s a better/best scenario.

A simple compost tea brewing set up using buckets and air pumps.It is vital to use quality water when brewing compost tea, and in your garden in general. If you are unsure of your water source, use a filter. There are quality reverse osmosis (RO) filters and de-chlorinators on the market for reasonable prices. Most nutrient solutions are not designed to account for what comes through the tap, so if possible start from zero ppm. Remember, chlorine kills microbes and it’s added to just about every public water supply in some form for this very reason. Bubbling your water will remove chlorine in a couple of hours, but not chloramines, its more persistent cousins—also used in many municipal water supplies. At the very least, let your water sit out for 24 hours before using it to brew tea. Ideally, invest in a reverse osmosis water purification system.

How to Apply Compost Tea to Plants

Adding compost tea to rainwater using a measuring syringe.You don’t need much! You can use as little as five gallons on an entire acre of land, roughly equivalent to about a one cup per gallon dilution. Some growers choose to use compost tea on every watering, but weekly applications or on reservoir changes are sufficient. It is even possible to experience benefits from compost tea with just one application. After all, you’re dealing with living organisms that can populate and reproduce by themselves if given proper conditions. Because you can’t overdose plants with too much compost tea (unless you are simply over-watering) it is particularly well suited for seedlings and cuttings.

Compost Tea as a Foliar Application

Compost tea works above the ground too! Weekly foliar applications of compost tea give great results. Compost tea can also help to control pests if used consistently, many bacteria found in compost seek protein, which is what comprises the exoskeleton of many target pest species.

Composts, Inoculants and Food Sources for Compost Tea

Some growers use worm casings as the sole basis for their compost teas. While this is certainly a viable option to brew tea, worms are predominately a bacterial organism, and do not contain some of the trophic levels of beneficial organisms, such as fungi, nematodes, protozoa, ciliates, etc. that provide vital benefits to plants and gardens. Worms sequester bacteria in their gut in order to work their magic, like termites use fungi to digest the wood they eat. To brew a better tea, consider using worm castings along with a balanced humus product.

Food sources for compost tea include molasses, kelp, fish, bat guano, and generally anything that was once alive that is soluble enough to be put into solution, even fruit pulp. It is important to note that recipes and preferences vary widely, for instance, some may recommend up to 16 tablespoons of molasses per 5 gallons of water, others only 1 tablespoon. Be sure to experiment based on these general recommendations, but here are a couple of simple recipes:

Three Simple AACT Recipes (All for 5 Gallon (19L) brewers)

Bacterial Dominant Tea

1.5 pounds (700g) bacterial compost or vermicompost
3-4 tablespoons (45-60ml) liquid black strap molasses
4 teaspoons (23g) dry soluble kelp or 2 tablespoons of liquid kelp
3-4 teaspoons (15-20ml) fish emulsion

Equal Ratio - Fungi : Bacteria Tea

1.5 pounds (700g) 1:1 fungi to bacteria compost
3-4 tablespoons (45-60ml) humic acids
4 teaspoons (23g) dry soluble kelp or 2 tablespoons of liquid kelp
3-4 teaspoons (15-20ml) fish hydrolysate

Fungal Dominant Tea

2 pounds (900g) fungal compost
3-4 tablespoons (50ml) humic acids
2 teaspoons (10ml) yucca extract
4 teaspoons (23g) dry soluble kelp or 2 tablespoons of liquid kelp
4-5 teaspoons (20-25ml) fish hydrolysate

Recipes reproduced from ‘The Compost Tea Brewing Manual’, 5th Edition by Dr Elaine Ingham.

Fish-based natural fertilizers are generally obtained in one of two forms, condensed fish solubles known as emulsions, or enzymatic digested fish known as hydrolysates. Fish hydrolysate is cold processed (minced, enzymatically digested and liquefied) to preserve proteins for quick turnover by microbes into nutrients for plants. Emulsions are created using extreme heat, and while they may be easier to work with because they are further refined, the processing removes valuable ingredients and denaturing nutrients. While both fertilizer forms can benefit a compost tea, hydrolysates retain the natural oils from the fish that are a very potent fungal food.

Mineral Catalysts

One thing that is not discussed enough in the compost tea community is the use of mineral catalysts. Catalysts, as we know, change the speed of a reaction. It’s important to understand that microbes work indirectly via chemical decomposition. In other words, bacteria don’t chew on a banana peel in a compost pile, they offer up an enzyme (biological catalyst) that works to chemically break it down. Enzymes are specialty proteins that work like keys to a lock for important biochemical reactions within living organisms, plants and people included. All enzymes incorporate a single molecule of a trace mineral—such as manganese, copper, iron or zinc—without which an enzyme cannot function. We all know the benefits of adding enzymes to our gardening systems, but not many growers know that you get free enzymes from microbes.

Microbes help plants eat and, in return, plants feed microbes. In fact, over half of the energy derived through photosynthesis by plants is fed to the soil as exudates. Think of an exudate as a meal for microbes. Plants actually know what they need, they just can’t tell us. This means that plants have the ability to attract specific trophic levels (imagine the balance of the big fish and the little fish in the ocean) of microbes by preparing food from its surrounding environment that attracts those capable of generating what is deficient in the plant. This biological/plant network, or intelligence, if you will, cannot be established overnight, but it can be tapped into if we are aware of it. This is especially true when growing indoors in artificial environments.

It’s important to provide everything for plants so they can be allowed to eat what they desire, but it’s even more important to allow microbes a complete tool kit. Not doing so is like hiring someone to build a house and only providing them half the tools. The pictures inset illustrates a side-by-side conducted with a broad-spectrum mineral product. The tea sample on the left was brewed in the presence of many more elements than the tea sample on the right. Note the enhanced foaming and darker color after only four hours.

Other catalysts to consider are rock dusts, yucca extract, or any broad-spectrum natural mineral. Remember, these materials are not “food” for microbes; they help microbes eat their food.

WORDS: Evan Folds