ACTIVELY AERATED COMPOST TEA
Although plants can grow and produce reasonably well in a sterile medium through the use of chemical fertilizers and pesticides, organic growing techniques produce the healthiest and best tasting food. Chemical additives, in general, are harmful to soil ecology.
The healthiest gardens, top yields and largest fruit and vegetable sizes result from special attention to soil health, particularly the rhizosphere. This is the zone immediately surrounding plant roots where, under ideal condition, countless millions of beneficial bacteria and fungi break down organic matter and release nutrients to the plants. These microorganisms in turn are the foundation for a healthy soil ecosystem, which includes protozoa, nematodes, earthworms, and various arthropods. A spoonful of rich, healthy soil should have millions of living organisms of hundreds of species.
Over the past several years, organic growers from around the world have learned that compost tea, particularly Actively Aerated Compost Tea (AACT), is an extraordinarily effective method for maintaining peak health of the soil ecosystem and the plants which depend upon it. The major function of an AACT is to inoculate the soil with huge numbers of beneficial microorganisms along with the food energy which they need to thrive. These will in turn, through their natural symbiotic relationship with garden plants, provide and release an abundance of minerals and other plant nutrients.
Following is a “recipe” for compost tea. This concoction is a composite of ideas from the books Teaming with Microbes, How-to-Grow World Class Giant Pumpkins The All-Organic Way, suggestions from online gardening forums, advice from other gardeners, and personal experience.
Equipment list for a low-budget, homemade compost tea brewer:
- Two 1-gallon buckets with lids
- One 5-gallon bucket with lid
- An aquarium air pump designed for at least a 20-gallon tank; the bigger the better, as it’s best to keep the water churning and bubbling well
- Aquarium air stones – at least four of them to disperse the air well; air stone rings would work even better
- Filter bag, cheesecloth or nylon stocking if you plan to send the finished product through any sort of nozzle
Materials for making one 5-gallon batch of AACT, which will be diluted 10:1 to 55 gallons just before application:
- 4+ gallons of rainwater or de-chlorinated tap water (accomplished by letting it sit for at least one day) – you’ll have a sloppy mess if you fill the bucket right to the brim
- 1 lb. worm castings, divided in half
- 1 lb. compost (mostly or completely composted), divided in half
- 2 oz. liquid humic acid (combined with fulvic acid and/or seaweed is even better)
- 1 oz. fish hydrolysate (fish emulsion works also, but is inferior)
- 1 oz. liquid seaweed (can prepare from dehydrated sea kelp)
- 2 oz. unsulfured molasses
- 1 tablespoon sea salts (trace minerals can really benefit plants, but take it easy on the sodium)
- 2 tablespoons phosphate rock dust
- ¼ cup powdered oatmeal (a kitchen blender works nicely for this)
- 2 tablespoons mycorrhizal fungi spores (optional, expensive, but very beneficial), divided in half
Step 1 – Planning.
Decide when, where and how much AACT you will need. You’ll need to start the process about 1 week before your planned application date. Plants can benefit from a light dose of AACT as soon as they are transplanted into the garden, or as soon as they are a few inches tall if transplanted from seed. For best results, apply every 2-3 weeks. Even one dose, applied early to mid season, would help. Likewise, applying a light dose every couple of days would not hurt anything – except for your time and money budget. If you already have a very healthy soil ecosystem, three applications per year should be sufficient.
How much? There’s some guesswork involved. Because I grow a lot of plants and tomatoes are my focus, I plan to apply one quart of diluted AACT per plant as the fruits start to ripen – two quarts or more when applying later in the season. Some recommend applying at least 5 gallons per acre as a soil drench.
Step 2 – Fungi
Fungi need a head start. They multiply more slowly than do bacteria, and they are much more delicate.
Combine ½ lb. worm casting, ½ lb. compost, ¼ cup powdered oatmeal, 2 tablespoons phosphate rock dust, and 1 tablespoon mycorrhizal fungi spores in a 1- gallon bucket. Stir well. Mix in about ½ cup de-chlorinated water. Keep adding water until the mixture is thoroughly moistened but not soggy. There should be no standing water in the container, but you should be able to squeeze some out.
Place this fungi incubator mix in a dark, warm (80°F) place for 4-5 days. A seedling heat mat should work well. On top of a fridge or a water heater should also suffice. Cover with a towel if necessary to keep the mixture dark. If all goes well, you should see a mass of white, gray, and/or brownish fungal mycelia start forming after three days or so. This “mold” indicates a healthy colony of fungus is growing.
Step 3 – Bacteria
Four to five days after starting the fungi mix, get the tea brewing bucket set up and the air bubbling. Make sure the bubbles come from the bottom of the bucket. A brick or rock might be helpful.
If you will be using a nozzle, it will be helpful to mix all ingredients except the water together first in a 1-gallon bucket, then transfer that mixture into a filter bag (or the equivalent, made of nylon or cheesecloth). This should then be suspended so that it’s completely submerged in the water column but not sitting on the bottom of the bucket.
If you will be applying the tea by dipping, all ingredients can be mixed directly with the water:
- ½ lb. worm castings
- ½ lb. compost
- 2 oz. liquid humic acid
- 1 oz. fish hydrolysate
- 1 oz. liquid seaweed
- 2 oz. unsulfured molasses
Stir the mixture well, and allow to brew for 36-48 hours at temperatures in the 75-90° range. More and faster aeration and higher temperatures can produce a completed brew in 24 hours or less. Less air and lower temperatures may necessitate 3 days or more of brewing. Froth should form and the brew should smell “alive and earthy” when the brew is ready. Once the source of air is removed, the tea must be used immediately. It can go stagnant (anaerobic) very quickly, resulting in the death of all the beneficial microbes you just raised. Plan to apply all the tea within two hours.
Step 4 – Combine, dilute and apply.
Stir in 1 tablespoon of sea salts. Up to ½ cup of magnesium sulfate (epsom salt) can also be added at this time if desired. Then gently blend in the fungi mixture. Note that the hyphal threads of the fungi are very delicate.
Dilute 10:1 with water and apply immediately. Again, de-chlorinated water is best, but hose water will do if that’s what’s convenient. Apply as a soil drench. Foliar application can also be very beneficial, particularly if done early in the morning while the leaf stomata are open.
Feedback and suggestions for improving this recipe are welcome, as my experience with compost teas is limited.
Should I add the fungal mixture to my compost tea bag and let aerate to mix or cut off the air stone and just lightly stir with hand? Was hoping to foliar and soil drench with the recipe and worry if I I don’t filter out the compost/castings it will clog my sprayer while foliar “feeding”. Awesome recipe, I’m really looking forward to using this one in conjunction with the others I currently brew.
Hi Adam, thanks for your contribution! In the nine years since I published this article, there have been significant advances in understanding soil ecology and in the technologies of producing high-quality compost teas. The balance among the different species of bacteria and fungi appears to make a huge difference in the effectiveness of the resulting brew. The experts use microscopes, clean laboratory techniques, and other technologies to produce the best blend. But in general, my understanding is that fungi are less resilient to agitation than are bacteria. So I would opt for the light stirring by hand, once the fungal mixture is combined. Prompt use is critical, especially for foliar spraying. Best of luck!