Compost Tea Considerations

By August Dunning
Published: October 16, 2018 | Last updated: May 4, 2021 08:25:14
Key Takeaways

Compost tea, or the stewing of aged compost in water, provides many benefits for the garden, the most significant of which are the micro-organisms and micronutrients present in a high-quality batch. Augustus Dunning has the details.

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For the novice gardener, compost tea is simply the stewing of aged compost in water for about three days to cause a bloom of micro-organisms that can benefit plants and restore soil. The main benefit of making compost tea is the micro-organisms that are grown in the process—the nitrogen in the compost is a constant and will not be increased by the brewing process and the strength of the tea will be based on the nitrogen of the plant matter in the compost.


Compost tea is a safe, non-burning, low-strength fertilizer that introduces critical and important soil-borne micro-organisms and micronutrients into a garden to improve the biodiversity of the soil structure and the delivery of micronutrients to plants.

Compost and Compost Tea: What's the Difference?

Any discussion about compost tea should be started off with a discussion about compost used as a fertilizer. Compost used as a mulch has documented abilities to suppress and prevent many soil-borne pathogens, is an excellent source of nourishment for plants and is a great soil builder. Typically, people put food waste, leaves, green trimmings, grass, wood chips, sawdust, dirt and other biological materials in a compost pile and let the micro-organisms and worms digest it over a year to make the compost we add to a garden to increase yield and nutrient value.


This will naturally contain the nitrogen, potassium and phosphorus used to grow the plant matter digested in the compost. It will also contain some minerals in different proportions depending on the plant type, so the value of the compost is directly dependent on the quality of the ingredients. For example, radishes extract more iron than beets from the soil. If you are using mineral-depleted crops as compost ingredients, the compost will be lacking in minerals. If you are using dirt in an area that is geologically deficient in certain minerals, the compost will lack certain micronutrients.

The value of a compost tea is therefore dependent on the quality of the compost and the regional soil elemental content, as well as the makeup of the biological matter—the subsequent micro-organisms such as bacteria, fungi and protozoa that will exist in the compost. The idea that compost tea is a panacea for all fertilization needs and garden problems is therefore not entirely correct, but it will in every way increase yield and help grow a successful garden.

The micro-organism population in soil produces metabolic by-products, in particular fulvates, which are electrolytes that move nutrients to roots. And just like the micro-organisms in a healthy human gut, they also make minerals available for uptake if minerals are present in the soil, but the micro-organisms and minerals have to be in a balanced state.


Fortunately, if you have worms, you probably have a balanced state. Mineral availability is a measure of the digestion of rock from crystallite solids into ionic elemental states. Because only ionic minerals can be absorbed by plant tissue, mineral availability is completely based on rock that has been digested into the atoms that made up the rock. Worm castings work because by the time the casting comes out of a worm, rock has been digested over and over by bacteria, microbes and nematodes into ionic elements that can pass into the cells in roots and then make it up to leaves to be used during photosynthesis.

But again, depending on the geological region you live in, some minerals may be lacking regardless of the organic process you use to provide a complete fertilizer of macro- and micronutrients from compost or in a compost tea. Minerals put nutrition in food, so they are critical for food to have health value.


If minerals are lacking, a supplement is one solution. Sea salts are not a good choice because salt is a disinfectant and will kill bacteria, reducing the micro-organisms. Powdered rock dust is another way to add minerals, but because the reduction of crystallite rock into ionic forms takes time, it may not provide useful amounts of ionic minerals by the time you want to use the compost for a compost tea. A better option is an ocean water extraction of all the elements in sea water with the salt removed, which can provide the necessary minerals in any compost tea regardless of the compost source used for the solution.

How to Make Compost Tea

So, with that in mind, making a great compost tea is actually pretty easy. Start with at least one-year-old, well-composted biological matter made up of a diverse range of well-grown, mineralized crop waste, brown leaves, bark chips, wood sawdust and forest floor dirt.

Add molasses and a mineral supplement to make sure the necessary sugars and minerals are available for the bacteria, microbes, protozoa and fungi because they need food for energy and minerals to grow rapidly.

An anaerobic compost tea applied as a foliar spray can prevent many diseases, while the aerobic compost teas have no effect in preventing disease. Both can be used as a foliar spray for nutrients.

Keep in mind that E. coli can be present in the raw ingredients in a compost pile. Minimize the risk by maintaining a hot pile or allowing the compost to mature fully and don’t apply compost tea to any vegetable crop within three weeks of its planned harvest date. Here are three different ways of making compost tea.

Compost Tea Recipes

Rotted Green Leaf Matter Method

  • Gather leafy materials like comfrey, nettles, lettuce, shard, spinach or seaweed.
  • Fill a bucket with water and put the leaves into the water.
  • Leave it to rot for about four or five days—the leaves will turn brown as the chlorophyll decomposes—then strain the solution and pour the solution on the ground around the plants.

Mature Compost Method

Often used in large-scale agricultural operations because anaerobic tea is proven to improve plants’ disease-fighting capabilities, this method is done without agitation or aeration so the anaerobic bacteria can thrive.

  • Fill a bucket half full with mature compost, add a mineral supplement and top up with water in the morning.
  • Stir the mixture at noon, then in the evening.
  • On the following five mornings, stir the mixture once to form a froth.
  • On day six or seven, it is ready for use. Stir daily thereafter. Don’t use after three weeks.
  • Strain if using as a foliar spray, or use from the bucket if in a watering can.
  • Apply in the morning, when leaf stomata open, for a foliar spray. Do not use in very hot or very cold weather.
  • Return the spent compost back to the compost pile.

Aerated Compost Extract [ACE] Method

This is a popular method because it actually increases the number of beneficial microbes by growing them in an aerated solution. This is my favorite because I have lots of oak leaves where I live and you need plenty of brown carbon source materials, such as dried leaves, bark chips, sawdust and forest floor soil (for the beneficial fungi content) in the compost. The compost has to be turned and aerated frequently to keep it hot (about 135°F) during its creation, so it’s well-composted before you use it. It will have an earthy, sweet aroma to it when it’s ready—if it’s sour or strong, it’s not ready yet. It takes about a year to ensure it is well-rotted before making tea.

  • Get a 10-gal. plastic bucket to use as a reaction vessel.
  • Install an aquarium pump in the reaction bucket with two or three large air stones.
  • Put ½ to 2 gal. of fully matured, aerated compost in the bucket and fill with clean, non-chlorinated water or rainwater (the chlorine in tap water will kill the micro-organisms and bacteria, so if you have to use tap water, put an air stone in a container with the water you want to use and run it for a day to get the chlorine to evaporate out of the water).
  • Add 4 to 5 oz. of molasses (un-sulphured) and stir so it is fully suspended.
  • Add your mineral supplement.
  • Stir this mixture well and let it steep for two to three days with the aquarium pump running to mix oxygen into the solution. Adjust the aquarium pump to about medium strength.
  • Stir the solution twice a day for three days.
  • On day three, smell the compost tea. It should not smell bad or have an alcoholic fragrance. If it does, add a bit more molasses and let it run for another day with the aquarium pump on high.
  • When the smell is musky and earthy, it’s ready to use. Leave the aquarium pump running to prevent anaerobic conditions from developing as you apply the tea, but you need to use it within one hour of taking it out of the reaction bucket.
  • Filter and use in a sprayer for foliar spray or use directly from the bucket for watering cans.

And there you go…it’s tea time!


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Written by August Dunning

Profile Picture of August Dunning

August Dunning is the CEO of Eco Organics and is a physicist, chemist and an inventor. He is the former systems ops designer for the International Space Station and a former regional manager of liquid, solid and electric propulsion systems for Pratt and Whitney space propulsion, Edwards AFB, NAWC and JPL.

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