Earth, by its very nature, is in a partnership with microbes of all kinds. From the deepest seas, to the highest mountains, microbes such as bacteria, yeast and fungi are a key part of our planet’s ecosystems, performing vital functions like making nutrients bio-available to plants and animals, and helping our soils maintain structure and moisture.
It turns out that we can take advantage of these symbiotic soil allies to great effect, and one of the easiest ways we can do this is by creating our own aerated compost tea. We’ll get into the how of compost tea, along with a recipe, in a moment, but first, let’s look at the why.
The main purpose of compost tea, besides adding a nice dose of pre-digested fertilizer to your garden, is to increase the number and diversity of beneficial microbes in the soil. How are they beneficial? Fungi, for example, help plants take up phosphorus, manganese, zinc, iron and copper, secreting digestive enzymes that dissolve and break down compounds so that plants can absorb them. They also dramatically increase the amount of water plants can take up, and act like a huge extension of their root systems. Other microbes predigest different compounds and help plants take up  different nutrients.
In addition to the aid they give us below-ground, microbes on the leaves of plants also may be important allies, helping in the fight against disease by both filling an ecosystem niche that would otherwise be open to pathogens, and creating conditions that make it difficult for existing pathogens to live or reproduce.
Many beneficial bacteria, for example, produce acids that make it difficult for pathogenic yeasts and fungus to thrive. Although there is less scientific study in this area, the theory that aerated compost teas help with above-ground diseases is borne out by my own experience. Last year, some haskap bushes on my farm had a nasty fungus infection on their leaves, so I mixed up an aerated compost tea and sprayed it on them. Within days the fungus had completely disappeared.
So, now that you know why it’s good to use compost teas, let’s get into how you can make your own. I’m going to go over making aerated and aerobic (oxygenated) compost tea specifically, but you can also make anaerobic (lacking oxygen) compost tea by simply putting a bunch of (ideally, deep-rooted) plants like comfrey into a bucket or barrel with non-chlorinated water, letting it sit for about a week until it gets really nasty smelling, and then putting it on your soil. (I would avoid plant leaves with this stuff). Another anaerobic mixture known as effective microorganisms is also incredibly useful and can be purchased online and then mixed up at home.
Aerated Compost Tea
- Bucket or barrel. At least 25 gallons is ideal for anything but the smallest garden.
- Air pump sufficient for the amount of water. You can get good ones at hydroponic shops. Tiny fish tank aerators are not the best ones, although they may be sufficient for a 5-gallon bucket.
- Non-chlorinated water. Chlorine in the water will kill microorganisms.
- Vermacompost and well-aerated compost are best. The more diversity of compost, the better. It should smell good, like forest soil, and not stinky. 5 pounds per 25 gallons.
- Unsulphured molasses. Food for bacteria, etc. 1 ¼ cup per 25 gallons.
- Liquid kelp. Fertilizer and microbe food. ½ cup mixed into 5 cups of water before adding to the mixture.
- Humic acid. Microbe food and soil conditioner: 1-2 tablespoons per 25 gallons, mixed into 2 cups of water before adding to the mixture.
- Rotten wood chips, straw or hay (optional). Decomposing high carbon materials encourage fungal inoculation. 1-2 cups per 25 gallons will do.
- Steel cut oats. Food for fungus. 1 cup per 25 gallons.
First, put the water in, then the molasses, and then add everything else. Some people like to put all of the solid materials into a pillowcase or similar (like a tea bag), but I prefer to mix them directly into the water. If you’re a little off in the amounts, it doesn’t matter, as long as you have enough molasses to sustain the microbe populations for the amount of time you will be bubbling your brew. I should also note here that a compost tea recipe can be as simple as compost and molasses. The other things will take it to the next level.
Next, stir the container well, and put in your air pump bubbler. It’s good to stir the mixture from time to time. Let it sit for 24 to 48 hours (the full 48 is better).
Once you’re done bubbling, remove the air pump and give it another good stir. Now it’s time to apply it to your plants. If you’re going to create a foliar spray for leaves (definitely recommended), let it settle and skim the liquid off the top so that it contains fewer solids and won’t clog your sprayer. To spray it, simply evenly cover the leaves on the top and bottom. For soil application, use buckets or other manageable vessels and dunk them into the stirred up mixture in order to get the solids as well as the liquid. Then, apply to the soil around the plants, ideally covering up to or beyond the drip line.
That’s all there is to it. You should notice a significant kick to your plant growth, especially if you do this every couple of weeks during the growing season. Just make sure not to fertilize beyond the first two weeks of summer in temperate climates, as this could prevent new growth from hardening off in time and you may lose it to frost.
Have you made compost tea? What recipe did you use? Share your compost tea tips in the section below: