Compost Tea

Compost tea is a brown liquid which has been actively aerated, it’s produced “by extracting bacteria, fungi, protozoa and nematodes (all members of the soil foodweb) from compost.” However, compared to compost, it’s an incredibly efficient method of injecting valuable nutrients into your soil (and plant foliage) and creating and/or maintaining the soil foodweb in your soil across small or large areas of land.  Dr Elaine Ingham, founder of the Soil Foodweb Institute, is responsible for flying its flag in a major way, traveling 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 Elaine 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. What’s that saying, the more you learn – the less you know. Anyway, here’s an overview of compost tea, some recipes and insights from various folks around the globe…

What’s the difference between compost tea & 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 one month in which time it becomes incredibly stinky, indicating that it’s gone anaerobic. 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 24-48 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.

What’s the soil food web?

It’s a complex collection of a trillion or so life forms including bacteria, protazoa, fungi, nematodes, cilliates etc. It describes the relationships between them and how they form a whole system which cycles nutrients through the layers of the soil, making them available to plants and other life forms, above and below the ground. You can read more about it here.

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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. If you check out the basic ecological succession chart below you can see the stages of succession and the areas where bacteria and fungi naturally flourish.

sfw Image adapted from here

There are a hell-of-lot more complexities and overlaps going on than this chart shows, but it gives you a general sense. When making compost tea, you can tailor the tea 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 which foster bacteria are nitrogen materials including manures and plant foliage, to attract fungi include carbon ingredients like wood chips. However, a good compost will have a healthy balance of bacteria and fungi suited for any crop. And 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 simplify it, here are two recipes and some great resources for you to go through.

Elaine Ingham has a basic recipe on her website which is centred around having *really* good compost, and a microscope. If you’re after something a bit more approachable, Hobart market gardener, Suzi Lam, has shared her recipe with us below.

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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 1/4 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.

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A good looking brew in process, those bubbles are a good indicator that things are going well, the other main indicator is the smell – it should smell sweet and earth.

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.

Can you put too much compost tea on your garden?

No, however 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.

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Is compost tea the answer to all soil problems?

Some people say yes, but we think no. 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 mineral/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.

Other good resources

2 Responses to “Compost Tea”

  1. Craig

    Nice summary. Teas are great for adding one-hit wonder soluble nutrients as well as long-lived biodiversity, so long as those microorganisms are kept watered and fed afterwards! Feed the soil to feed the plants.
    A recent long term study showed that adding leaf litter increased the fungal dominance in soils due to the increase in soil organic matter, but perhaps not biodiversity, which the teas can add. Apparently soil organisms contribute up to 40% of the organic matter available to plants, while litter (leaves etc.) contribute 60%. So getting the biology right can be 40% of the job, just enough to get the plants going for you to then chop and drop that 10+% needed to close the loop. Whether they can amend every type of soil may depend on the organisms you select for, but as Elaine Ingham says, all soils already contain all nutrients required. Note the word “soil” and not dirt, and “nutrients” and not minerals. 🙂
    To feed the soil there are two pathways for litter to add organic matter to soils. Fast and slow. And fresh is best here, as the more soluble nutrients are absorbed relatively quickly by microorganisms as the non-structural parts of plant matter breaks down. Then the structural parts break down much slower forming larger particulate matter humus. So chop and drop, or chop, shred and throw seems to be the way to go! The permaculture way…

    I’m a stickler for details… and Suzi Lam’s recipe using air stones is not recommended as they are impossible to clean and can contaminate subsequent brews. A container with sharp corners is also not recommended for the same reasons, but everyone does it! Many aquarium pumps also lack the output required to raise the dissolved oxygen levels of the brew over 5.5ppm, and preferably 8ppm.

    Reply
    • Hannah Moloney

      Nice points Craig, you’re spot on – I chose not to go into so much detail, as well there’s just soooo much of it isn’t there!
      I’m aware that Elaine Ingham says all soils have all the nutrients they already need, but personally I’m sceptical. Some soils are so out of wack with minerals for growing food (especially in Aus) that adding some minerals can be the most efficient way to ensure nutrient dense food. Steve Solomon has researched and written a lot on this (link to his book in the blog).
      Interesting point on using air stone – I didn’t ask her about how she cleaned them, but she’s incredibly thorough this women, so I wouldn’t be surprised if she has a system. Personally I don’t use them and have an ‘air blower’ instead of aquarium fish pumps (as recommended by Elaine Ingham). Thanks again for your comments :-).

      Reply

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