Aerated Compost Teas

After reading the compost tea section of “Teaming with Microbes”, a book I highly recommended, their DIY compost tea setup was simple enough that I decided to try it out. At the end of the post I will include pics of my setup which is super easy, relatively cheap (very cheap when compared to commercial stuff) and produces a completely filtered compost tea ready for application with a sprayer or watering can. But first lets talk a little about actively aerated compost teas (AACT).

If you’re an organic gardener, of course you know the benefits of compost, whose praises have been sung far and wide. The smell of fresh, healthy, finished compost is one of my favorite smells in the world. That earthy aroma in a good compost is the smell of billions of microbes going about their microscopic business as they break down the organic matter and feast on it (and each other!). After reading “Teaming with Microbes” I now have have a vastly new appreciation for the mind blowing, complex ecosystems of microbes that exist in our gardens. They live and die by the trillions within the soil, at the roots of plants (rhizosphere) and on plant leaves (phyllosphere). A well aerated compost is shock full of these guys.

With an actively aerated compost tea, compost is soaked in water and aerated with a commercial aerator or other aerating device like an aquarium pump. The constant movement of the bubbles both provides air to the microbes in the compost and teases them out of the filter and/or soil medium so they can multiply within the tea solution. A good aerated compost tea is like putting compost on steroids (very briefly – and, you know, in a healthy way).  In AACT the bacterial population can explode from a mere 1 billion per tsp to 4 billion per tsp. Since it is aerated, these are still the same kinds of organisms that we encourage when we build an aerated compost pile. Of course, AACT is NOT compost because it doesn’t contain the copious amounts organic matter that compost does and so all these happy microbes living in your AACT need a place to go and eat before they start to eat themselves (yikes!). To feed them, let them go to town in your yard. The authors report that it is virtually impossible to over apply compost tea. Even if you watered your plants ONLY with a AACT, the microbes will adjust to the amount of available nutrients on the leaves and in the soil. It will not burn roots or leaves and they state “it will only help increase the diversity of microbial populations in your soil”. They recommend a twice a year application, but if you really wanted to go crazy you could apply AACT as often as you water.

The reported benefits of aerated compost teas are numerous as the folks at Soil Food Web Inc eagerly demonstrate in this article. Because the tea is so rich in microbes, it is a good for the restoration of soil after chemicals have been used on it. Even synthetic fertilizers can be devastating to the life in your soil, so frequent use of compost tea is great for transitioning to organic gardening. An added benefit of compost teas is that they can be applied to leaves. So while compost can only be used directly to improve the diversity of the rhizosphere (roots), compost tea can be used improve the diversity of the phyllosphere (leaves) as well as the rhizosphere. Aerated compost teas are also reported to help suppress disease, but unfortunately not a ton of study has been done on aerated compost teas. I recently read a crotchety article (pdf) about the “myth” of disease suppression. Something isn’t a myth until proven false, so I prefer “unproven hypothesis” since at this point in time, a thorough study has not been done particularly on the disease suppressing abilities of compost tea. Which means we have to experiment and judge for ourselves at this point. So lets get to it! At the very basic level we know that healthy plants repel insects, and healthy environments promote healthy plants and healthy environments are ones with lots of soil diversity…….ergo……AACT is a good tool in your gardening tool box. With each application of a compost tea is the chance that another lucky beneficial microbe will find their unique place in your garden ecosystem.

A few guidelines for brewing and applying teas:

• For foliar application, apply to both sides of the leaves if possible
• Apply it in the morning or evening as the heat and wind of the day will reduce the microbe’s chance to get a foothold
• Use aerated compost tea immediately after brewing as the populations will begin to die off once aeration stops.
• Brew your tea at room temperature, colder temperatures inhibit growth, hot temperatures fry microbes.
• A good aerated tea should be coffee brown and have a rich earthy smell.
• The height of microbial growth is between 24 and 36 hours.

A simple starting recipe for a five gallon batch is non-chlorinated water, 2 cups compost, 2 tablespoons of molasses, fruit juice, cane syrup or maple syrup (to get the party started). To de-chlorinate water, let your aerator run in the water for about 2 hours before adding tea ingredients. If you have a recipe that you would like to share or have had obvious success with compost tea, please comment below. I am just beginning and would love to know more. When posting a recipe, if you could include a little detail on why you use that particular recipe that would be awesome.

Here is my simple setup: all told it cost me maybe $30 and produces more than enough tea for my 1/4 acre yard. It took me, mmmm, 15 minutes to assemble and get my first brew bubbling.
1 Aquarium pump (Tetra Whisper for 40 gallon aquarium – probably overkill, but hey I want bubbles!)
3 feet of clear 1/4″ tubing
2 feet of 1/4″ soaker hose (for drip systems)
1 3 prong 1/4″ tee for drip systems, used to put the soaker hose in a hoop
1 5 gallon bucket
1 pair of Size Q pantyhose

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The tea pictured above is my first mix, called Kablooey! tea. I used fresh stinging nettle, worm castings, finished compost and orange juice.

The method above is a filtered application for use as a foliar spray and topical soil drench. There are other methods that include a lot of organic matter and could be a beneficial soil additive. For some more ideas, check this article out.

Here is an interesting post of someone using a couple different compost tea methods to try and get weakened plants to buck up.