Use of Compost teas

The decomposed organic matter present in compost improves soil quality and provides nutrients for the plants. However the billions of bacteria, fungi, protozoa, nematodes and other micro organisms which form the living components of compost are often forgotten once they have completed their role in making the compost.  

  Compost tea increases the benefits of normal composting by boosting the microbes in the soil and also acts a liquid fertilizer supplying soluble nutrients which can be used by plants. Compost tea cannot be over-applied and can be used at any time of year. It is recommended for use on plants  every 14-30 days during the growing season. However, it can be applied once a week to help control disease or when soil quality is poor.

It can be used as:

1) Foliar spray adding beneficial organisms to plant so disease-causing organisms cannot find infection sites or food resources and to provide nutrients as a foliar feed.

2) Soil application to help develop the biological barrier around roots, to provide nutrients for roots to improve plant growth, to improve life in the soil in general, with effects on soil structure, water holding, root depth and improve nutrient cycling, nutrient retention and disease suppression.

 (The Compost Tea Brewing Manual Elaine R. Ingham, PhD.  Soil  Foodweb Incorporated) 

Compost Leachate

 This secdtion is included on the Compost Tea page for the benefit of those coming directly to the page without using our list of contents.

Leachate is not a compost tea it is liquid that has percolated through and drained from feedstock or compost and has extracted dissolved or suspended materials. This run-off from the compost bin or heap differs from compost tea which are made from mature compost in that   leachate  will include organisms  from a mix of immature and mature compost collected as the water  passes through the heap. Fewer microbes  than will be found in teas will are extracted from the compost but the leachate will contain a range of  the soluble nutrients that were in the compost. The  enzymes, proteins, hormones and other materials present do  not disappear as rapidly as in a compost extract.

To go to our page on Compost Leachate click here Compost Leachate.


Choice of Compost

The key to making good compost tea is the initial compost used. The best home compost for the purpose is  from a hot heap as this will tend to have a good supply of beneficial   microbes and higher fungal counts than cold compost heaps. If possible, check of the presence of bacteria, fungi and protozoa  using a microscope Hot composting also kills potential pathogens. Where the fungal count is known to be low it can be increased in any compost by the addition of Fish hydrolysate  or a handful of steel cut oats to the compost a couple of weeks before brewing. Another method of increase the fungal count in the compost before use in making tea is to mix it with a small handful of coarse oatmeal (UK), or steel cut oats (US) for at least  two weeks before brewing

Specially formulated compost for use in making Compost Tea developed to provide a balanced compost rich in bacteria, fungi and protozoa can be purchased from brewing equipment suppliers.

There are two main types of compost tea Non-Aerated and Aerated. In the following sections we will consider the merits of the two types.



Non-Aerated Compost Tea (NCT)

Non-Aerated Compost tea being made in two ols Bokashi bins.
Gutter down-pipe with pop-sock used to filter the tea.

NCT  is  made by  simply soaking   sweet-smelling  mature aerobic compost in water. Soaking and stirring removes  microbes as well as  soluble nutrients from  the compost  so that the finished tea  will  contain the range of enzymes, hormones, microbes, nutrients  and plant growth compounds found in the original mature compost. The tea will reach low oxygen levels or be anaerobic is minimal if mature compost is used.  The full food web may be present if oxygen levels do not drop below the levels required for aerobic respiration. 

On the allotment or in the garden the procedure is convenient  requiring little time and effort as the compost is just soaked and stirred periodically.

NCT may  contain non-beneficial anaerobes because the air surface of the container cannot provide enough oxygen  for  microbes in the lower portions of the container to respire aerobically. The likelihood of anaerobic conditions occurring increases if the compost used is immature. One of the reasons that non-aerated compost teas  do not normally have additional food sources added to the brew as this will also increase the likelihood of  anaerobic conditions.  Tea in which anaerobic conditions have been allowed to develop will be less effective as a foliar feed.

 Simple Compost tea in water was traditionally  made by suspending a sack,  cheesecloth bag,  a  pillow case or an old  pair of tights,  containing compost in a barrel or bucket of water for 7 to 14 days. The bag should be suspended by string from a rod across the top of the bucket but completely submerged in the water (a stone can be added to the bag as a weight) The microbes will be  filtered through the material to give a liquid feed that could be applied with a watering can or a sprayer.  Some methods suggest putting holding the “sack”  on the bottom of the bucket using a stone.  If this technique is used  when making any teas or feeds it is best to tie it with string which reaches outside of the container to make it easier to remove.

The technique has been modified slightly over the years using different water containers e.g. buckets or water butts and filtering the liquid after the tea has been made rather than soaking it in a sack. Under this “free compost” variation, which makes easier to aerate the mix and mechanically remove organisms by  stirring, the compost is left loose in the water and filtered at the end of the process. The tea needs to be filtered through muslin or an old pair of tights to avoid it blocking the watering can  rose when being applied to the plants or soil.  I use a short length of plastic drain pipe with the leg of a pair of tights over one end as a reusable filter. 

Every composter seems to have their own variation on the basic to suit their site and the materials available.

Basic Non-aerated Compost Tea Recipe: 3-4-day brew

Mix: Using a spade add  freshly harvested, mature  compost to third fill a bucket and then add water almost to the top of the bucket (unchlorinated rain water if available). If using chlorinated tap water, it is best to fill the bucket the night before use or degas the chlorine from fresh tap  water by stirring  vigorously for 10 to 20 minutes before adding the compost.

 Soak: Different sources recommend different soaking (brew)  times from  3-4 days to several weeks. The longer period and regular stirring enable more organisms to be extracted from the compost.  Stirring also adds some oxygen to the solution. If  the mixture is
left unstirred for a long period, the it is more likely that the resultant feed will contain a high proportion of anaerobes.

Strain: It is necessary to filter the liquid to avoid it blocking the rose of the watering can, or spray,  be using to apply it.  After the 3-4 days  strain the liquid through an old pair of tights,  cheesecloth or other porous fabric (burlap) , into a second bucket. I find that  a three-foot length of downpipe with one end covered by a “pop-sock” works as a reusable filter.  If washed out between sessions the pop-sock will last several months. The sludge that remains in the bucket, after filtering, should be added to the compost bin. Alternatively, the compost can be contained  in a pair of tights, burlap sack etc. before being added to the water. While this avoids the need to filter the finished liquid it does mean that the compost will not be as effectively washed when stirred.

Dilute: The filtered liquid is diluted with rainwater until it is the colour of weak tea,  or 10 :1 ratio of water : tea, and used immediately.

 Non-aerated Compost tea:  10-day brew

Mix: Three quarters fill a 5-gallon bucket with non-chlorinated water.(If chlorinated must be used treat it as described above) and add about 2lbs of mature finished compost and stir well.

Soak: The brew is stored in a warm but shady part of the garden for 10 days where it is  stirred frequently. The tea can be used immediately or  stored for up to 6 months, If the tea is stored it should be checked to ensure that it smells healthy. If it has an unpleasant odour it has turned anaerobic.

Strain: Strain through  cheesecloth or  tights as above.

Dilute: Dilute 1:5- 1:60 with fresh rain water or unchlorinated water before applying to plants, lawn, and soil. 

  Non-Aerated  Worm Compost Tea

Finished worm compost is an excellent compost for use when making compost tea. It can be used on its own or 50:50 with conventional compost ideally prepared in a hot composting system from predominately green waste compost. I spade full of is put into a pair of old tights, cheesecloth or pillow case into 5-gallon bucket of rainwater of one, r two days or even just over night. Alternatively,  the compost can be added directly to the water and be filtered after soaking. I prefer this method as it allows the compost to be stirred or aerated more effectively than if it is contained in tights

Dilute until it is light brown in colour, not unlike weak tea, and use immediately before the beneficial microbes in the start to die.

The sludge left in the bucket can be used on the garden or be added to the compost bin as a way of supplying  moisture and activator to  the bin. 



Compost Extract

Mash bag with the first towel full of fresh compost. The bag should be filled.

Compost Extract

 Simple Compost extracts can be made in less than 20 minutes, making them very convenient if there is not enough time to brew aerated tea or to leave the compost for a long soak.   While the extract will contain a lower population of microbes  than compost tea made from the same compost it  has a longer shelf life. Aerated Compost tea only  has a shelf life of only 3-4 hours, while it is claimed that an extract has a shelf life of 1- 2 weeks. I recommend checking the smell of the extract before use to check that  it has not turned  anaerobic. If anaerobic  it will  have an unpleasant smell and should not be used

The extract will also contain the range of soluble nutrients found in the original compost. Extract nade wifrom compost produced from feedstock with a good C:N  ratio, when applied diluted 1:3, it has been shown to reduce growth of some weeds. so I would suggest using this dilution.

Compost extracts require a larger volume of compost than teas. It is recommended to use about a kilogram  (or 3 cups) in 5 gallons of clean rainwater. It can be used as a soil drench, to boost the soil  round established trees on lawns  and even as a   root dip during  transplanting. Both the liquid and compost remaining in the bag makes a useful  activator added to  compost heaps. 

The Extract can be made agitating or vigorously mixing  compost in the water, or by running water at pressure through compost. I use sieved compost. The easiest method of doing this is to put the compost in a mesh screen bag, as would be used for making aerated compost tea. Put the bag in a container of clean rainwater and leave until the compost is soaked. I use a a 25l open container in which I have marked a 5gallon "fill-line" this gives plenty of room for mixing and makes it very easy to  ladel out to finished extract using a childs watering can.    Some recommended gently squeezing the bag so that the maximum number of microbes and nutrients are released.  The bag can be agitated for a few minutes so that the water washes through the compost. The bag is then left for another five minutes, and the agitation repeated.

If made in the “bag” it will probably not require filtering before use.


Actively Aerated Compost Tea (ACT or AACT)

Aerated Compost Tea is a compost extract brewed with an added  microbial food source such molasses, kelp or rock dust. Worm castings or good mature aerobic compost, preferably the result of hot composting,  full of beneficial microorganisms is required as an inoculant together with a means of  constant aeration during the brewing process providing at least 6ppm of dissolved oxygen  to  create  an aerobic environment throughout the brewing process. The pump should produce enough bubbles to agitate the liquid.  If available worm castings are the compost of choice as  worms break down their food using bacteria instead of digestive acids. The castings are therefore high  in beneficial microorganisms. Worm castings are also a good source of humic acid, a good food source for the tea.  Aerated Compost tea (ACT) offers advantages over that made without aeration in that it contains more  micro-organisms, as the aerobic brewing process aids the extraction of microbes from the compost and provides favourable conditions for them to multiply during the 24- to 36-hour brew period. 

 It  can be applied as either a soil drench or as a foliar feed. The finished tea  should   contain all the species of organisms that were present in the original  in the compost. The tea making process is usually  facilitated by the adding additional  nutrients to assist the  microbe growth  e.g.   black molasses/treacle, kelp or  liquid plant extract such as  nettle soup, comfrey tea or even  dandelion wine, in the tea brew as well as to the finished tea, immediately before application, encourage adhesion to the plant foliage when sprayed. These additives may be purchased premixed as  Compost Tea Catalysts and may be purchased to be added to commercially available brewing equipment. Purchased Compost Tea Catalyst and “Compost such as MycoLife provide  a consistent inoculant whereas each batch of home compost used will be different depending on the ingredients used in making it.

Home  compost can be pre-treated by mixing  it with some humic acid or fish hydrolase  two to three days in advance to encourage microbial . The pre-treated compost can then be added to the water.

Compost teas shoukd be used immediately  and certainly within a few  hours, as during the brewing process the feeding and oxygenation will have  resulted in more  microbes being produced than can supported  in the liquid and they will soon turn it anaerobic.

No matter what type of compost tea is being made it is worth checking it regularly. It should have a fresh earthy smell. If it smells unpleasant it is likely to be turning anaerobic , the simplest cause of action is to discard it and start again. With NACT that smell have a slightly unpleasant smell I would put it to one side the see whether the smell disappears as the aerobes return.

The other important factor is cleanliness. Once the tea has been decanted  thoroughly clean, you’re the brewing  equipment with  soap and water and then ensure it is dried.

 The simplest and cheapest method of making ACT is in a bucket aerate by aquarium bubblers.

Bucket aerated tea

There are many variations  on making Compost Tea suitable for use by home composters  using a 20 litre or 5-gallon  bucket  normally aerated by two aquarium aerator stones or bubblers powered by a good size aquarium pump. As these require electricity to run the pump, they are non-suitable for use on most allotments. Although  the  aerator stones will provide a continuous flow of air  which should create sufficient  turbulence to distribute the oxygen it is recommended  to stir the tea  during the brewing process.

 Option 1

Half fill a 5 gallon  the bucket with compost having broken up any lumps  and fill to within 3 or 4 inches of the top with non-chlorinated water. Put two aquarium aerators/bubblers in the water,  weighted so that they  sink to the bottom of the bucket. Stir in about an ounce of black treacle (molasses). Stir regularly throughout the 2- or 3-day brewing process. At the end of this time, after turning the aerator pump off, leave the  brew to  settle for  about 30 minutes.  This allows  most of the solids in the compost to settle to the bottom of the bucket making filtering the tea easier. The liquid can then be carefully poured off into a clean bucket without disturbing the sludge which can be added to the compost bin.  The liquid portion of the brew can be filtered through an old pillowcase, tea towel, or pair of tights. 

Option 2

 In this variation the  air stones or bubblers are taped to the bottom of the bucket using waterproof tape, the bucket is  half-filled with unchlorinated water which is aerated for  for 10 to 20 minutes before adding the compost. Compost is added to bring the water level to within 3 or 4 inches of the top of the bucket. Add molasses or one of the other food sources mentioned depending whether a bacterial of fungal tea is required. Brew for at least  2 to 3 days

Option 3

Although most recipes seem to use molasses or black treacle, I have been looking for a food source that might be more readily available to the home or allotment composter and would suggest that white sugar offers a viable alternative. As with the previous methods a 5-gallon bucket  containing about 4 gallon of non-chlorinated water and two aquarium bubblers are used. Four tablespoons (1 per gallon)  of white sugar is added. This is mixed with two cups of fresh matured compost. I also suggest providing  an additional source of nutrients such as nettle or comfrey juice  or liquid seaweed. This  compost tea catalyst is stirred into the water  and aerated for two days.    


Solar powered bucket aerated tea

Normally when making  "bucket" aerated compost tea  the use of aquarium pumps with two or three bubblers below the surface of the liquid are recommended but this needs an electricity supply which few of us have near our compost bins.

 A cheap solar powered pond aerating pump is quite effective although will of course only operate during sunny days and there is a risk of the brew becoming anaerobic  or at least suffering a decrease in aerobes during the night. I  used such a system on the allotment, where there is no electricity, for a number of years, during the summer and the brew has always had a good composty smell and never adversly effected plants. 

Half fill the bucket with compost and fill to within 3 or 4 inches of the top with water and add the aerator. Stir in about an oz. of black treacle (molasses). Stir regularly. After three days harvest the tea filtering through an old pillowcase, tea towel, or pair of tights.  

Aerated Worm Compost Tea

Aerated worm compost tea  can be made using the same recipes as normal Aerated Compost Tea (ACT)  but recipe is offered using black treacle added to the soaking compost to provide additional nutrients to encourage bacterial growth, and aeration to increase the population of the beneficial microorganisms.     

Put a shovel full (about 1 gallon) of  finished worm castings directly  into a 5-gallon bucket  add 4 gallons of rain water  and a tablespoon full of black treacle. Aeration can be by means of an electric aquarium filter of a solar powered pond pump.  Ensure the air stone or bubbler is at the bottom of the bucket. I fix it in place by tying it to a wire support.  Allow the tea to brew for 3-4 days, stirring occasionally.

Strain the tea using gauze, tights. I fit a pop-sock  over the end of a short length of plastic rainwater downpipe to make pouring easier and to allow the same filter to be reused.

Use the tea immediately to water your garden plants and seedlings or as a foliar spray.

Types of Aerated Compost Tea and Brewing Times

The following use recommendations are taken based on the recommendations contained in "How to make Compost Tea" by the Garden Tea company




Brewing time


Balanced ACT

Approx. equal Bacteria: Fungi  biomass ratios



Most vegetable crops, grasses, flower and herb gardens, berries, fruit trees

Bacterial ACT

Bacterial biomass

12 -24 hours


Brassica family crop

Fungi/ Humus Teas

Fungal biomass

36 –48hrs 

Deciduous and conifer trees, orchards, vine crops shrubs and  acid-loving plants.


Additives for home brewed ACT

Choice of additives to favour groups of organisms

The following materials can be considered when making “Compost tea catalyst” at home



Bone Meal, Corn or Maple syrup, Fish Emulsion, Sugar (cane or white), Yeast extract

 Bacteria & Fungi

Humic Acids, Fruit Pulp, Organic Molasses(or treacle), Rock Dusts, Sea Kelp,


Cellulose, Fish Hydrolysate, Ground Oatmeal, Lignin, Oat Bran, Soybean Meal

Brewing systems

A wide range of brew kits are available to the home and allotment gardening ranging. We will be looking at these in more detail shortly:

BubbleSnake Compost Tea Aerator by TeaLAB

  Bucket systems such as the   BubbleSnake, which comes with Brew Bag, Air Pump and Tubing (571GPH Air Pump) for use in a 5 gallon bucket which utilises a “BubbleSnake”  instead of Air Stones.  The BubbleSnake Aerator is a simple device creating larger bubbles that mix currents in the brew vessel, ensuring a well oxygenated system. 


Flo-n-Gro Brew Compost Tea Brewing System.

 A  3 gallon compost  tea brewer supplied complete with comes, air pump with hose, Eco 185 submersible pump, fountain kit and 2 air stones. Uses a  “'fountain head” design to keep the solution agitated. £134.07 from Amazon.


Symbio’s Home BioBrewer's produce brewers for the home gardener and allotment holders. Designed with affordability and ease of use the new Home and Garden Compost Tea Brewer (25L) costs  £43.19 – £62.57 for the average size garden 15L costs £27.00 – £45.824I

The kit does not include a compost tea bag in which to suspend the compost during aeration. These are available on the internet (do shop around there is a considerable variation in price)  or an old pair of tights can be used.  A filter sock can also be purchased but I filter the tea using a short length of plastic down pipe  with a pop-sock over the end.

25litres of tea will treat 1,500 sq. metres of soil using 333g of compost to make the tea.


XL ProBio 20/50 Brewer

50 litres of brew will treat 1 hectare (ha).  The XL ProBio 20/50 brewer is very flexible allowing the brew to range  from the minimum to the maximum volume of compost tea at a time. The base is fitted with a disc diffuser  But it is not cheap being more suitable for the trade £475.00

Growing solutions

 Growing Solutions uses a Fine Bubble Diffusion dynamic aeration process. Each Fine Bubble Diffusion aeration disc has 4,000 engineered perforations (1mm in size) that provide consistent air bubble size and velocity. 40 litre brewer 

  • Symbio 25l brewer

    The Symbio 25l Compost Tea Brewer with pump and aerator

  • Compost bagged and being aerated

Homemade Pesticides: Regulations

The following advice is taken from the HSE website. I have included it as background information as some homemade products, made in a similar way to liquid feeds, are  used as pesticides e.g. rhubarb leaves

Agricultural, horticultural and home garden pesticides are regulated under the Plant Protection Products Directive/Regulations and the Control of Pesticides Regulations.

Agricultural, horticultural and home garden pesticide products are those that are used to protect plants e.g. insecticides, fungicides, herbicides (weed killers), molluscicides (slug killers), plant growth regulators and bird and animal repellents.

HSE are aware that some gardeners routinely use home-made remedies that are not authorised to control pests, diseases and weeds. In some cases, these remedies are simple physical barriers and are outside the scope of UK and EU regulations. In other cases, these remedies involve the use of chemicals either from foodstuffs, like coffee grounds, or from household products which are not normally intended to be used as pesticides.

Part of the legal definition of a plant protection product takes into account the intended use of the product. For example, garlic extract sold as a foodstuff doesn’t require authorisation under plant protection product regulations, but garlic extract sold as an insecticide does. In practice this means a number of own use home-made remedies such as beer traps or coffee grounds fall outside the scope of regulations.

However, this does not mean that use of these remedies including use of common household chemicals as a pesticide is without risk or that it is always legal. For example, in circumstances where a home-made remedy was supplied to another user (whether free of charge or not) this may fall in scope of the regulations, and if so, would be illegal without an authorisation. In this sort of circumstance, where HSE (or other enforcing authorities) obtain evidence of such a supply or use we would need to consider appropriate and proportionate enforcement action.

Volunteer gardeners

An increasing number of members of the public are getting involved with allotment societies or volunteer groups taking on larger gardening projects which may previously have been undertaken by paid contractors. For example, volunteer groups now manage parts of some public parks, take on ‘Britain in Bloom’ or similar projects and some allotment societies are now responsible for maintaining the whole allotment site rather than just individual plots. These activities span the borderline between amateur and professional uses of pesticides.

For further information


04.12.2022 06:31

Jeremy Musgrave

Do you have any data on ' application ' of Aerated Vermi Compost Tea to Mangoes and benneficial outcomes .

06.07.2020 12:33

Tatiana Sokoloff

Hi there. Can I get onto your email system please? I live in theDominican Republic where composting is still a novelty and soil is so sterile seeming. Hardly a worm!