Compost tea is an incredibly efficient method of injecting valuable nutrients into your soil.
Compost tea is a brown liquid which has been extracted from compost and actively aerated in a process that extracts bacteria, fungi, protozoa and nematodes, all members of the soil foodweb.
Dr Elaine Ingham, founder of the Soil Foodweb Institute, is responsible for flying its flag in a major way, travelling the world educating people and working with farmers to integrate it into their land management systems.
Now, I'm no compost tea expert. Sure, I've completed a short course with Dr Ingham and am in love with all things compost, however this stuff's deep, and despite years of experimenting, I still consider myself a novice.
But here's a brief overview of compost tea, some recipes and insights from various folks around the globe.
Compost tea vs plant-manure tea
Pant-manure tea is the age-old practice of soaking manures or a range of plants in a vessel of water where they leach their nutrients into the water.
This can include compost, beneficial plants (comfrey, borage, dandelion to name a few), fish guts and animal manures.
It's then left to 'stew' for up to a month and becomes incredibly stinky, indicating that it's gone anaerobic, "without air".
I remember working on a farm and having to spread very mature plant tea around the market garden. No matter how many swims I had in the dam I stank for days.
In contrast, compost tea is an aerated brew which doesn't smell bad (at all) and is usually ready between 24 and 48 hours depending on the weather and ingredients.
The liquid is aerated through an air blower (or fish pump), or if you have no power by stirring it vigorously regularly. By getting air into the liquid, the right environment is created for diverse soil foodweb to form.
So while both provide nutrients, the compost tea also provides life to the soil - and that's what we're after.
The soil food web
The soil food web is a complex collection of a trillion or so life forms including bacteria, protazoa, fungi, nematodes, cilliates.
It describes the relationships between them and how they form a whole system, that cycles nutrients through the layers of the soil, making them available to plants and other life forms, above and below the ground.
When you think about the type of compost tea you'd like to make, think about what crop you're trying to grow, this will determine the ingredients you need to put into your brew.
For example all annual vegetables naturally thrive in a bacteria-rich environment, whereas orchards and other tree crops naturally evolve when fungi dominates.
Tea fit for every crop
When making compost tea, you can tailor it to suit the crop you're growing.
So if you're growing annual vegetables, make a compost tea with more bacteria and if your growing tree crops, favour the fungi.
Ingredients that foster bacteria are nitrogen materials including manures and plant foliage, to attract fungi include carbon ingredients like wood chips.
However, a good compost tea will have a healthy balance of bacteria and fungi suited for a variety of crops.
Fungi is the ultimate soil life form for any crop - in our own garden we actually put a significant amount of carbon into our annual crops by using ramial wood chips to attract fungi ... I told you it was complex.
To help simplify it, here is a recipe from Hobart market gardener Suzi Lam.
Compost tea recipe
Suzi brews her compost tea in a 20 litre bucket for up to 48 hours and dilutes it to (approx. 10:1) to water her quarter acre market garden.
It's important to note that you need dechlorinated water, if you're on town water, simply leave a bucket of water out for 24 hours for the chlorine to evaporate before you make your brew.
Bubbles are a good indicator that things are going well during the brew process, the other main indicator is the smell - it should smell sweet and earthy.
An important tip is to clean all the materials thoroughly after you've finished so there's no 'scum' left on the bucket for air blower, otherwise there's risk of contamination for the next brew.
Everything needs to be clean and fresh, you can use hot water and elbow grease to clean.
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How much is too much?
While you can't really put too much compost tea on your garden, there's no need to do it every week. Make and apply compost tea strategically to help get a crop started or just before fruiting.
Some people say compost tea is the answer the soil problems, but we don't think so. Specifically, it does not resolve mineral imbalances. It may help - but as far we understand things, it cannot fix it.
We recommend approaching soil remediation by first doing a soil test to determine the nutrient content and then using a range of methods which can include compost, compost tea and possibly (depending on scale and context) applying some minerals to help bring everything back into balance.
A good book to read about using minerals and growing nutrient dense food is The Intelligent Gardener by Steve Solomon.
- Hannah Moloney and Anton Vikstrom are the founders of Good Life Permaculture, a permaculture landscape design and education enterprise creating resilient, regenerative lives and landscapes.