How to Make Aerated Compost Tea

Latest Update 10th March 2017.

Note*.  Dr Elaine Ingham is the founding president and director of research at the Soil Food Web Inc. and knows all there is to know about aerated compost tea.  I have posted links to some of Dr Ingham's video presentations in my blog under "Soil FoodWeb" (left hand sidebar).  They will change your understanding of how soil ecosystems work.  This link is an example of her easy to follow presentations.

Aerated compost tea is a crucial tool in Dr Elaine Ingham's fight against the degradation of soil around the world.  In combination with light applications of good quality compost It can restore soil productivity in a season or two.  Its amazing and her efforts are gaining credibility and momentum around the world.

The microbiology behind the use of aerobic compost tea is very technical and beyond the scope of this article or of the average backyard gardener, and Dr Ingham's main focus is on commercial growers who have soil quality issues.

To correct nutrient deficiencies, farmers need to regularly test their soil biology under the microscope., and they need to control the mix of microbes in their compost and in their aerated compost tea to ensure they are delivering the appropriate soil condition and nutrients for the plants they wish to grow.  I don't do any of this.

The cost and time involved in having microbial count soil testing done is easily justified for farmers, its harder to justify for the backyard gardener.  So I use aerobic compost tea to maintain highly beneficial microbe activity on the roots and on the foliage of my plants.  I leave restoration of degraded soil to others.  However if you have degraded soil, you should take a look at The Soil Foodweb Inc.

My soil has been mainstream organic for many years, and has been productive and full of biological activity.  So I'm starting from a strong position, but I do know that ordinary garden soil responds very well over a short time frame to a substantial top dressing of high quality homemade compost and regular applications of aerated compost tea.

I use aerated compost tea to increase microbial activity on roots and foliage to not only boost the nutrient uptake of the plants I grow but also to provide protection against soil pathogens and airborne pests and diseases.
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Making compost tea has changed the way I garden, and getting a better handle on the role of micro fauna in the soil and on the above ground tissue of plants has transformed my thinking about organic gardening.

Aerated compost tea is made by brewing a small quantity of first rate homemade compost in clean rainwater (or filtered tap water) and adding nutrients to feed the microorganisms in the brew (example recipes below).  

Mains water contains unwanted additives like chlorine and fluorine which kill microbes, but if you aerate it for an hour before adding the compost and nutrients, you can remove most of these chemicals.  Although I always use rainwater I still aerate it overnight to increase the oxygen concentration in the brew and give the process a flying start.

The compost tea ingredients are added to the water and the mix is aerated for 24 hours.  During this time beneficial microbes and plant nutrients are extracted from the compost and the microbes multiply rapidly as they consume their food.  When finished the brew will contain four times as many aerobic micro organisms as there were to start with.

At the end of the process, the brew is filtered through a paint straining bag to remove solids, and the remaining tea is used as a foliar spray.  You can dilute it to 4 parts rainwater to 1 of tea if you have a large area to spray, but I like to keep mine at full strength.

The tea needs to be used within an hour or two of brewing because the aerobic microbes quickly use up the oxygen supply when the pump is turned off.  These beneficial microbes become dormant without oxygen and eventually anaerobic microbes take over.  When this happens, the brew can become contaminated with plant pathogens.

A foliar spray of aerated compost tea delivers huge numbers of beneficial microbes to the plant.  They form dense colonies and suppress the activities of microbial plant pathogens.  These colonies are firmly bonded to the plant's foliage and a mutualistic relationship begins.  In exchange for carbohydrates and sugars made by plants during photosynthesis and exuded through their leaves, beneficial microbes help feed the plants and keep fungal and other foliar pests at bay. 
I use a 20 litre food grade plastic bin with lid to contain my brew.  The brew is made up of rainwater, liquid fish extract, liquid seaweed extract and homemade compost.


Recipes.

A. General Purpose Tea.  In very small gardens where it is impractical to make up 2 different brews, a general purpose recipe makes sense
  • 15 litres of captured rainwater.
  • 60ml of liquid fish extract. (fish hydralysate is best)
  • 30ml of liquid seaweed extract.  (kelp is best).
  • 150 grams of good homemade compost. 
B.  Vegie Patch Tea.  With vegetables and annual ornamental plants, you get an almost instant benefit from a quick acting bacterial brew.
  • 15 litres of captured rainwater.
  • 25ml of liquid fish extract.
  • 45ml of liquid seaweed extract.
  • 150 grams of good homemade compost. 
C.  Orchard Tea.  A high fungal option benefits established plants, like trees, shrubs, perennial herbs and ornamental plants.
  • 15ml of captured rainwater.
  • 8ml of liquid fish extract.
  • 150 grams of good home made compost.
Mix the fish extract with the water and sprinkle it onto the compost in a cardboard box 3 days before brewing.  The box will absorb any excess water from the mixture.  Keep it in a warm spot at 20-30 degs C.  After 2-3 days the compost will develop a "fuzz" on its surface.  Laden with fungal spores, it is now ready to be brewed.
  • 15 litres of captured rainwater.
  • 60ml of liquid fish extract.
  • 30ml of liquid seaweed extract.
  • Prepared compost.

Useful resources on this subject:-

The Soil Guy.
The Permaculture Research Institute.