Barreca Vineyards

Barreca Vineyards

From Vine to Wine since 1986

Compost Tea Time

When I moved to this property 35 years ago, I put a well ring on top of the ground near the garden.  I thought that I could use it to make manure tea and then siphon the enriched water to the plants in the garden to both water them and add fertilizer.  That never got going for a number of reasons, but the well ring has served as a contained planting area for crops that spread like strawberries and mint.  It actually works well for that but the manure tea idea has fallen out of favor for a number of reasons, not the least of which is the smell.  It turns out that smell is a good thing to keep track of, but I’m getting ahead of myself.

Lately I have ramped up my equipment to make biochar.  Biochar is great at absorbing water.  It is a little like vermiculite that way.  But unlike vermiculite, it also stores carbon in the ground for hundreds of years because it doesn’t biodegrade.  That also means that it is not itself a nutrient source for plants or microbes. It’s more like a hotel for organisms that live in the water it stores.  You could let it collect bacteria, fungi, nematodes and protozoa from your own soil once it is mixed in and watered.  But if you are using biochar to help build your soil, maybe that is not the best place to start.  Inoculating biochar with a healthy mix of microbes right from the start really puts the “bio” in what would otherwise just be charcoal.

Compost tea is a great way to get good microbes into biochar.  Biochar is created in a fire and you won’t find any microbes surviving the heat.  Using compost tea to quench the biochar fire is not an option.  You need to wait until the charcoal has cooled down.  Just as it is for humans, 70° to 80° is a pleasant temperature for microbes and for growing compost tea.  In the middle of the winter that can be a challenge.  Ironically, the best place I found for making compost tea was my root cellar.  Sure it is near 34° in there, but at least it doesn’t freeze and with a heating pad or two and an old blanket, bingo! 80°.

Compost Tea setup with blanket around heating pads and air pump

If it were only that simple…  You can’t use manure tea on a certified organic farm.  Besides the good result of lots of readily available nitrogen, bad actors like E. coli and Salmonella can breed in manure tea. You don’t want them near leafy greens or any vegetable you are going to eat directly.  “Escherichia coli (abbreviated as E. coli) are bacteria found in the environment, foods, and intestines of people and animals. E. coli are a large and diverse group of bacteria. Although most strains of E. coli are harmless, others can make you sick. (” That is why my original manure tea well ring was not such a good idea.  Not only was starting with manure dangerous, letting it just sit in the water turns out to be frowned upon.  There are two basic kinds of compost tea, anaerobic that just sits in water for however long you want and actively aerated compost tea (AACT) that grows microbes in a vigorously bubbling container for 24 to 36 hours and then is used within 4 hours.

Friends told me there was a big difference between aerated compost tea and anaerobic tea, so I looked it up under “aerated compost tea”.  There are lots of links.  I liked and The basics are not too hard and I will get to that.  The first obvious question is why is aerated compost tea better?  The simple answer is fungi.

You want a balance between bacteria and fungi.  Bacteria are good at breaking down lots of different nutrients and making them available to plants.  But they are not good at digesting wood and fiber.  That is a job for fungi.  Additionally, mycorrhizal fungi can form symbiotic bonds with plant roots and bring water, minerals and other nutrients to plant roots in exchange for sugar.  Most fungi need oxygen. If you need fungi in your compost tea, you need to bring in oxygen, hence the aeration.  It also helps to get your microbes from an aged compost pile.  The fungi are more abundant there.  And you need to feed them starchier kinds of material like grains and potatoes.

Being in over my head at this point, I called on the North Columbia Monthly’s resident fungi expert, James Groth, asking how to know if my compost tea is balanced between bacteria and fungi.  He replied “Trying to quantify fungi and bacteria in compost, even with a microscope, is impossible, in my opinion.  There are hundreds (probably thousands) of kinds of both, with different life styles.  I would agree that fungi are mostly aerobic, but so are many bacteria.  Anaerobic bacteria are not desirable in compost.”  Remember I mentioned smell in the first paragraph. Articles on AACT like the one in tell us that the finished tea should have a “sweet earthy smell, coffee brown color and bubbles on top.”

In his book about Korean Natural Farming, JADAM, Youngsang Cho argues strongly against aerobic digestion and for anaerobic fermentation.  He notes that is used to make wine, Kimchi and yogurt.  Aerobic digestion uses up the nutritional elements that humans and animals need.  He favors anaerobic digestion because it does not need mechanical aeration and can make nutritional soil teas from simple ingredients like leaf mold, boiled potatoes and sea salt.  So both methods of making compost tea have their advocates.  One downfall of anaerobic digesters is that they can produce methane.  It not only stinks, it is a greenhouse gas that is 30 times more powerful than carbon dioxide and can last over 100 years in the atmosphere ( 

Luckily, the aerated compost tea in my root cellar had a sweet smell.  Oddly enough, it started with socks.  Clean old cotton socks to be clear, but I did have to sew up the holes in them.  There are lots of special “tea” bags recommended for aerated compost tea, but socks work just fine.  The critical parts are the starter microbes from worm castings or finished compost and the microbe food.  Recommended foods include molasses, fruit, juice, fish emulsion, oatmeal, rock phosphate and fruit pulp.  My best batch (judging by the smell) was from barley and weak apple cider left over from a wine making project.

The trickiest part actually is getting the aeration going.  The gismo in the picture is an aquarium air pump, VIVOSUN 317-1750GPH Commercial Air Pump.  After I bought it, I was pleased to note that the same pump was pictured in several articles about AACT.  It comes with an array of valves that lets you aerate up to 6 different buckets.  I used ¼ inch drip irrigation tubing to get the air into the bucket and held the ends down by sticking them through an old metal plumbing part.  That air pump really gets the water roiling as recommended.  I was glad however that it was down in the cellar away from the house because it is pretty noisy.

Don’t get the idea that AACT is just for biochar.  None of the articles I read even mentioned biochar.  It can be used regularly to pep up garden plants (but I would still avoid putting it on leafy greens).  There were many uses as a foliar spray that acted as a fertilizer and even as pest control on perennial plants.  It is supposed to control apple scab for instance. Still you need to think of it as a burst of microbes that need something to live on.  Mulch, compost and grass clippings make good food for the soil biome.  Add some compost tea and your soil springs to life.  Spring time is tea time!

One Response to Compost Tea Time

  1. I like the succinct bio-char explanation. I’ll need to give the compost tea sites a look; seems to be a lot going on there.


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