Actively Aerated Compost Teas - Nature’s Miracle Grow

Jefferson Edward

Two CowsWhat would you think if I told you there were supposed to be two cows worth of biomass in every acre of garden or farmland we tend? Crazy right? Well while we can all be pretty sure no one has buried a cow in our roses, as we learned from my article,  The Soil Food Web: Life Beneath Our Feet, in the previous issue of the FoodWise Newsletter, underneath our feet is a plethora of life known as the soil food web. In this web of life, a teaspoon of healthy soil contains ~ 1 billion bacteria of between 20,000 and 30,000 species, several yards of fungal hyphae, a few thousand protozoa and even a few dozen nematodes. They may be small, but they are many and together they create the equivalent biomass of 2 cows per acre of soil.

The question then becomes, do you have a healthy soil in your garden or on your farm? Perhaps, but if you are using Miracle Grow or something similar probably not. These fertilizers are salts which are dissolved in water and applied. This is an unfortunate series of events for soil life, particularly bacteria and fungi because of a process called osmosis. Microbes lock up in their bodies a large percentage of water in the soil. When salt fertilizers are added to the soil they create a high solute condition. Through osmosis, water (a solvent) moves from the low solute condition inside the microbes through the cell walls out to the high solute condition, killing the microbes in the process. This creates not soil, but dirt… basically a medium to hold roots while you feed the plant nutrients and water.

An alternative approach is contained in the old organic gardening adage, “feed the soil, not the plant.”  The best way to create the "two cow" approach to agriculture is to give your soil copious amounts of compost, spray compost tea (specifically Actively Aerated Compost Tea or AACT), on the leaves and soil around the plants and then top dress with a mulch (wood chips, straw, pine needles, fallen leaves). AACT’s aren’t hard to make, but the process is a little more than dumping compost in a bucket, adding water and letting it steep.

Soil bacteria

The idea behind AACT’s is to “brew” the microbial life of compost as an aerated nutrient solution. In an environment
where the dissolved oxygen is above 8mg / liter of water and plenty of food is present, bacteria and protozoa multiply rapidly and fungus grow into long strands called hyphae. In other words, all of the players in the the soil food web are highly concentrated in a solution that can be sprayed directly on the soil surface and plant leaves where they can interact with each other, releasing nutrients to the plants through processes described in my previous article.

ACCT’s have two different recipes for the brew, one is bacteria dominate and the other fungal dominate. This depends primarily on what one uses for food in the solution. Which one you need depends on where you want to apply the AACT. Soil bacteria end up being in highest concentrations in areas where nitrogen levels are high and decomposition of organic materials are rapid, such as pastures, fields and gardens where we grow annual crops that need high amounts of nitrogen. Soil fungi are responsible for the decomposition of woody materials so higher concentrations tend to be found in forest and orchard soils. So you might tailor your recipe to match what kind of soil you're feeding.

Or, which recipe you use may also depend on what you are growing:

  • Conifer trees that drop large amounts of woody material  - highly fungal
  • Decidious trees that drop some woody materials - moderately fungal
  • Perennials with fruit or perennial flowering plants - balanced bacterial and fungal
  • Most vegetables and pastures - moderately bacterial
  • Vegetables of the brassica family - highly bacterial

Mycorrhizal hyphae

Soil fungi growing in the root zone of green plants often create a "mycorrhizal mutualistic association [symbiosis, which] provides the fungus with relatively constant and direct access to carbohydrates, such as glucose and sucrose. The carbohydrates are translocated from their source (usually leaves) to root tissue and on to the plant's fungal partners. In return, the plant gains the benefits of the [fungi]'s higher absorptive capacity for water and mineral nutrients, partly because of the large surface area of fungal hyphae (pictured), which are much longer and finer than plant root hairs, and partly because some such fungi can mobilize soil minerals unavailable to the plants' roots. The effect is thus to improve the plant's mineral absorption capabilities.

While how to make compost is beyond the scope of this post, if you are making your own compost then the carbon/nitrogen ratio of your compost materials will determine whether you will have a bacterial or fungal dominated compost. If you use vermicompost or worm castings, your AACT will definitely be bacteria dominate. Otherwise, as a rule, the more brown material you add to the compost (old straw, dried leaves, sawdust, cardboard, shredded newspaper), the more fungus will dominate your compost. On the other hand, the more green material you add (kitchen scraps, lawn clippings, coffee grounds, blood meal) the more your compost will break toward being bacteria dominated.

I prepare the following recipes in a 5 gallon pail as follows: Use a paint straining bag as a "teabag" You can purchase one at a hardware store. These have holes big enough for the larger biota to flow through. Blend the compost, soil and dry ingredients and fill the teabag. Put the teabag in the pail and fill the pail non-chlorinated water (if your water is chlorinated, fill the pail the day before and leave it uncovered so the chlorine can gas off). Stir the liquid ingredients into the water. Set up your air pump (see below) and turn it on. Let the pump bubble your AACT for the recommended "brew times."

Balanced Compost Tea Recipe

Brew Time : 48 to 72 hours

2 cups of balanced compost
½ cup garden soil
½ cup forest soil
¼ cup of humic acids
¼ cup of liquid kelp
⅛ cup of kelp meal (gives fungal strands a surface to form)
⅛ cup of unsulphured black-strap molasses added at the beginning of brew
⅛ cup of unsulphured black-strap molasses added 24 hours after the brew has been started. *

*Black-strap molasses contains a number of beneficial minerals that feed the microbes, but it is not recommended by Elaine Ingham, I haven’t had the chance to find out why but my thoughts are it causes to much of a bloom of bacteria which uses up the dissolved oxygen too quickly to allow the other microbes to multiply. 

Bacteria Dominated Compost Tea Recipe

Brew Time : 48 hours

2 cups of worm castings
½ cup garden or pasture soil
⅛ cup of cane sugar or, better yet, pure maple syrup
⅛ cup of soluble kelp
⅛ cup fish emulsion

Fungal Dominated Compost Tea Recipe

2 cups of fungal-dominated compost*

1 cup forest soil
⅛ cup f ish hydrolysate
¼ cup humic acids
⅛ cup of yucca extract
⅛ cup of liquid kelp
⅛ cup of kelp meal
⅛ cup of ground oatmeal*

*The brewing process tends to get fungus to multiply in a short brewing process, I like to inoculate the fungal based compost (field saturation level of moisture) with ground oatmeal and place it in a lightly covered container in the dark for 4 or 5 days prior to brewing. When you open the container you will see fungal mycelia growing through the compost, use this product for the brewing process.

Finally I want to address the air pump. Regular aquarium sized air pump don’t have enough output to get the required oxygen concentrations. I use EcoPlus brand Commercial water aeration pumps and I use the EcoAir 1 model for a single 5 gallon bucket and EcoAir 3 for 2 or possibly 3 buckets, you will have to experiment to see. Instead of air stones I use the EcoPlus Water Wind Micro Bubbler Rings as I have found they are the best for keeping the brew bucket aerated at the proper levels. 

Actively aerated compost teas are the best addition to any organic gardeners toolkit. They can be sprayed at the rate of 5 gallons per acre, but you can’t use too much so spray at will. This with the addition of compost and mulch will make any garden productive beyond anything you can do with Miracle Grow. AACT’s and the soil food web are the true miracles of man working with nature.

About the Author:

Jefferson Edward is a student of all living systems, budding herbalist and simple living coach.

September 1, 2017