Jan 012015

If you are a gardener who tries to reduce your impacts on the natural environment, you will be using methods which avoid manufactured fertilisers, pesticides and herbicides and which minimize waste. So you’re into composting and worm farming and mixing the resulting solid material into the soil. However, at many times of the year a liquid fertilizer in the form of a “tea” may give plants, especially vegetables and fruit trees, a boost that is quicker than applying the manure, worm castings or compost which release their nutrients much more slowly. Such teas can be made from compost, weeds and other greenery and manures. How do you make and use them? What are their pros and cons? The advantages of using teas are said to be:

  • They provide nutrients for you plants more quickly in the soil than the solid material used to make them.
  • The microbes in them make soil nutrients available and help prevent soil and plant diseases, something that commercial fertilisers do not do.
  • They are cheaper than commercially manufactured fertilisers.
  • Unwanted plant material in your garden can be turned into something really useful.
  • They make the garden more self-sufficient by recycling material it has produced.

On the other hand, because the effect of teas depends on the quality of the starting materials, how the teas are made, the climate, when they are applied, the plants they are used on and the state of the soil before their use, there is debate about their usefulness, with some findings that they can be harmful.

Extracts and teas

Don’t confuse extracts and teas. The simplest, but not the best, method of making a liquid fertiliser from your garden material is to make an extract. This is made by covering some compost, worm castings or manure with water for a few hours or days. Nutrients and minerals from the solid materials dissolve in the water and microorganisms present on the solids can enter the liquid. This can then be used by either applying directly to the soil or, when diluted to the colour of weak tea, as a foliar spray. However, these extracts are inferior to teas which have been brewed.

Why bother making a tea?

If properly brewed, teas provide much more than minerals and other nutrients. They are also very rich in microorganisms, a mixture of bacteria, fungi, protozoa and nematodes, which can fight plant disease-causing organisms in the soil and on foliage and can convert soil nutrients into forms that can be taken up by plants. They usually take longer to make than extracts and may involve more effort. For many gardeners and organic farmers, making compost tea is both a science and an art. And there are many different opinions about what method is best and, indeed, whether they work at all.

Compost tea

IMG_0001To prepare compost tea, put mature compost into a container like a bucket or plastic rubbish bin. You can put compost straight into it or into a “bag” which can be made from a piece of shade cloth or other material with small holes like old net curtains, stockings of panty hose. Cover the compost with water. It is preferable to use rain water, filtered water or mains water that has been allowed to stand for 24 hours to allow the chlorine to off-gas before adding to the weeds. The removal of chlorine makes it easier for microorganisms to multiply. You will need to add something to start the process off by providing easy to access nutrients for microbial growth. The best additions are brown sugar or molasses but others could be some fish meal, some canned fish which has been allowed to “go off”, grain meal, fish food, rotten fruit, compost, garden soil or finished compost. Nitrogen rich vs sugar rich additions give different results in terms of favouring bacteria or fungi.

Then there are two ways you can brew the tea:


This requires aeration. This process provides oxygen which allows aerobic microorganisms to multiply rapidly and break down the plant material. You could use a stick, which means you will need to stir it several times a day for about 10 days. In between stirring, cover the bucket or bin loosely so that air can enter. But unless you really like physical exercise and can remember to stir each day, using a fish tank aerator for about 3 days is a good alternative. There are many websites which provide ideas for you to make your own compost tea aerator, and there are even some commercially available assemblies.

Tea made this way will not smell unpleasant and should be used straight away. There are different opinions about how long the tea should be brewed. It really depends on your compost, the temperature and the nature of aeration. At some point, aerobic microorganisms will have used available nutrients and not be getting enough oxygen, so anaerobic microorganisms will take over. At this stage it will start to smell wiffy – but don’t despair. You can use it quickly before the aerobic microbes all die (because there will always be a few aerobic microorganisms) or let it go on brewing under anaerobic conditions.


Some practitioners recommend that it might be better for home gardeners to use the easier anaerobic method which does not involve aerating and favours microorganisms which do not require oxygen. Just cover the container fairly firmly and wait for about 3 weeks. It requires longer and tends to be smellier but still produces a useful product. Some say that after the anaerobic microbes have finished, aerobic ones will take over again. But as I indicated, there is some controversy over this.

Worm tea and worm farm leachate

Most of us are also familiar with the liquid that comes out of the worm farms – called names such as worm wee, worm juice or worm tea, but really is a leachate. It contains plant nutrients, but is not rich in microorganisms like compost tea. Worm leachate really needs to be used cautiously since it contains “bad” bacteria as well as “good” and may be harmful to plants, especially if it smells “off”.

For worm tea, the castings from a worm farm can replace compost in the teas described above.

IMG_0005Weed tea

The best weed tea is made from plants with deep roots like comfrey, dandelion and nettle since they have incorporated minerals that have been leached from topsoil. Making weed tea is also a great way of extracting nutrients from plant material you don’t want in either your garden or in your compost heap where they would start multiplying. It also includes plants with runners and those which take root easily.
Follow the methods described for compost tea but it may be necessary to weigh the weeds down between stirring because they may float.

Manure tea

Animal manure can be used to make a tea by the same methods as for compost tea. However, there is a high risk of producing a brew which contains organisms which can be harmful to both plants and humans, especially if it is anaerobic. An extract, however, is a quick way making a nutrient-rich solution, but it will not have the same benefits as a microorganism-rich aerobic tea.

Using teas

Remove the bag which contains the solids and let it drain into the container. Or if you haven’t used a bag, pour the liquid through some shade cloth or other fine material laid in a soil sieve. It would be wise to do this wearing rubber gloves (and perhaps a peg on your nose!) since this might be a pretty potent and smelly brew. Put the solid material into your compost heap where it will break down further.

Remember, teas contain living organisms and should be treated with respect. Sun and heat can kill them, so apply them to the garden early in the morning or after dusk. The most useful times of the year to use them appear to be early spring, several times during the growing season and towards the end of autumn so that the organisms can work in the soil over winter.

Handle the brews carefully with gloves and don’t apply to vegetable leaves that will be eaten, especially if anaerobic and smell bad, since it is possible that pathogenic organisms are present. Use the tea diluted one to ten as a foliar spray, or less diluted if applying to soil.

And don’t expect miracles – results depend on so many factors that they are impossible to predict. We’d be interested in hearing of your experience.


Lowenfels J and Lewis W. (2010) Teaming with microbes. Timber Press, Portland, Oregon.
What are the Benefits of Aerated Compost Teas vs. Classic Teas? http://faq.gardenweb.com/faq/lists/organic/2002082739009975.html
Secrets of Making Compost Tea.www.compostjunkie.com/making-compost-tea.html

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