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Making Vermicompost Tea

A topic that a lot of people getting into (or already involved in) vermicomposting seem to be interested in is that of ‘worm tea’ – also known as vermicompost tea, worm castings tea, or just plain compost tea. Many assume that worm tea is simply made by collecting the liquid that drains out the bottom of a worm bin (if it has drainage, that is), but this isn’t really the case.

In actuality that liquid is referred to as leachate, and definitely isn’t nearly as good as real worm compost tea. The problem with leachate is that it can contain all sorts of compounds produced in partially composted or anaerobic waste materials – some of these can actually be phytotoxic – that is to say they can harm or kill plants. If you dilute the leachate with aged water and aerate it for 24 hours or so, it should be fine. Also, when it really comes down to it, if you are simply pouring the stuff out in your garden (i.e. large area, lots of microbes) it’s probably not that big a deal. I’d be more concerned about using it directly on potted plants.

High quality vermicompost tea is made from…drumroll please…high quality vermicompost! Whether you make it yourself or purchase it, the material should look and smell like really rich black earth – the higher the percentage of actual worm castings (worm poop) in it, the more it should resemble coffee grounds. If you happen to be using a rubber tub type of worm bin, the material you harvest may be pretty wet, and not exactly what I would called ‘high quality’ stuff – at least not yet. I’d recommend simply airing it out once you have separated the worm from it. You can do this by spreading it out on a plastic sheet in a dry location – if outside, you might want to keep it in the shade just so you don’t completely bake all the life out of it.

The actual making of worm tea is very simple. I’m no tea guru myself, but I do know the basic principles, and in my humble opinion that’s all you need to make some great compost tea.

Here is a basic supply list:

I simply poured two watering cans full of water over top of my muslin bag of vermicompost (which is tied at the top)

The amount of vermicompost used is up to you. For the batch I made today I used approx. 500 ml (I filled up a empty cottage cheese container). Academic research has indicated that worm compost is pretty potent stuff, with a little going a long way. So you really don’t need a massive amount to make a batch of tea – especially if you are adding some extra microbe food. Speaking of which, many of the serious worm tea brewers out there swear by a wide variety of additional amendments in their teas – materials like rock dust, kelp etc etc can apparently help to boost populations of the ‘good’ microbes, while adding some additional nutrients to the mix.

I added about a tablespoon of molasses for kicks and giggles – again, I am no expert here, but I do know this will help to boost microbial activity in the mix at least somewhat.

Lastly but certainly not leastly (thats a word – honest!), I plugged in my air pump to start aerating the tea. I will likely leave it going for 24 hours or so.

That’s pretty much it! Something I’ll likely do while the tea is brewing is move the tea bag around a bit just to make sure I’m getting a lot of the good stuff out. Normally (in an actual compost tea brewer) the bag would be suspended in the water column somehow to maximize flow of water through it, but I have little doubt that my mix will do just fine with the aeration and some addition shaking of the bag.

I’m not 100% sure what I’m going to use the tea for. I’m thinking about trying it on my big Hollyhock plant which has been suffering from various ailments and attacks from pests over the last few years. I gave it quite a bit a vermicompost this year, which definitely seems to be helping, but I think a foliar application of the worm tea might help it even more.

Anyway, I will keep everyone posted, and will certainly be talking a lot more about worm tea and vermicompost in coming weeks/months.

[tags]worm tea, vermicompost tea, compost tea, compost tea brewing, vermicompost, worm castings, worm compost, compost, compost tea brewer, beneficial microbes[/tags]

Written by Bentley on July 2nd, 2008 with 25 comments.
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Get your own gravatar by visiting Patricia
#1. July 15th, 2008, at 8:18 AM.

I really like the idea of compost tea. I have alot of leachate (4 gallons) on a daily basis so I really haven’t made too much effort to aerate castings. If I wanted to give tea as a gift to friends, and I put it into a container would they need to dilute or use full strenght? I would think either way would be ok. Love this site and all the great info! thanks bunches.

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#2. July 16th, 2008, at 2:21 PM.

Hi Patricia,
Wow – 4 gallons of leachate? Sounds like you have quite the operation going there (based on other info you have shared as well).
Worm tea as a gift is a nice idea, but I would suggest making it with castings, and would also suggest giving it to the person shortly after making it. You definitely don’t want to leave it sitting around for any length of time once you are finished aerating it.

You don’t necessarily need to dilute it though. Worm castings aren’t strong like bat guano etc, so there is no worry about burning your plants or anything like that.

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#3. July 16th, 2008, at 9:55 PM.

That is exactly what I thought. 4 gallons is alot for me as I do have worms in american recycling bins and the worms are awesome!! I would definitely use castings for my tea which is my project for today. I also remember reading on one of your sites about using it right away so that makes sense. I think I will just give them castings in a burlap or something bag and let them make their own. Recently at a fair, I bought some coconut coir from a guy for $10 a block(not a brick) and am planning on mixing some coir with manure and start a new pile soon. Have been reading up on it lately. I am confused about why you need to add gypsum though? Or did I misread? TIA

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#4. July 17th, 2008, at 5:23 PM.

Hi Patricia,
Gypsum is basically the same thing as ‘Lime’ (Calcium carbonate), and is used to prevent the pH from dropping too low in worm bedding. Generally, this would only really be an issue with peat moss bedding since it is quite acidic – coir on the other hand is neutral as far as I know.

I personally think there is too much emphasis placed on the use of Lime in worm bedding. Composting worms are very tolerant of a wide range of pH, and I’ve actually read that they would actually prefer pH 5 over pH 7 or 8 – which kinda makes sense when you think about the sort of habitat (compost heaps etc) they live in.

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#5. September 30th, 2008, at 7:54 PM.

Hi Bentley
Hadn’t heard of adding Molasses before – will give it a try. Say, I have been running the tea thru a sieve prior to bottling, as that way it can be sprayed on plant foliage and not plug-up the sprayer. Vegetable plants seems to love to take in the nutrients this way and it also repells various leaf-eating pests. I’ve always wondered, however, if I might be sieving too many microbes out by doing this. Any thoughts?

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#6. October 1st, 2008, at 2:13 PM.

Hi DeAna,
Unless you are using a decent filter, you won’t be losing too many microbes. It is important to remember that most of them are incredibly tiny, so the holes of most sieves would seem like vast open gateways to them.

Get your own gravatar by visiting mary
#7. February 22nd, 2009, at 9:11 PM.

Thank you for such complete and easy to understand instructions for worm tea. Raising the worms is easy but my worm mentors who gifted me with this bin were not able to help me know how to use it. You have taken care of that detail and now I will send the information back to them. A nice ‘payment’ for a special gift.
Also, thanks for the info on the mites. It just shows that every creature has problems.
Thanks. Mary

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#8. February 24th, 2009, at 4:09 PM.

Thanks, Mary – glad to help!

Get your own gravatar by visiting Mark
#9. June 16th, 2009, at 9:53 PM.

Just a clarification, gypsum is calcium sulfate, not ground lime (calcium carbonate). If you are organic, you can’t use drywall, also gypsum, because of the possible chemical contamination. Best to use mined gypsum.


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#10. January 27th, 2010, at 5:17 AM.

I am not able to grow fungi in my compost tea. I use best vermicompost and add some seedcotten meal, mollases and fish powder or without fish powder. Finally I can see many bacteria and protozoa but without any fungi. would you please help me Why fungi not able to boost in this solution ?

Get your own gravatar by visiting Andreas
#11. September 12th, 2010, at 8:24 PM.

I read in a blog of a guy who is cultivating compost worms to feed his koi fishs that he is using the worm tea of its culture as a “bacteria starter kit” for fresh worm food.

He is pouring a lot of water over its worm box every few days (which is not for gaining compost but just to feed the koi) to keep it wet and he collects the “worm tea” that is dripping out after this action.
When preparing new worm food he is pouring the worm tea over the vegetables and card boards to settle the bacteria-cultures directly on the new stuff.

Now after i have read this (and found it logical) i use the worm tea of my can-o-worm (a closed plastic system with a tap) to inoculate the new worm food with the bacteria and fungus of the worm-tea and store the freh food for a few days outside the worm house to prepare it for faster utilization by the worms. It’s actually also easier for me to keep the new-food “aerobic” this way as i can stir it up to bring air inside without disturbing the inhabitants of the worm-box.

I just started this practise so i don’t know well it really works.

Get your own gravatar by visiting Bentley
#12. September 14th, 2010, at 4:07 PM.

KIOMARS – I’m not really sure why you are not seeing fungal numbers. I suspect the folks at Soil Foodweb Inc or similar organizations would have a much better idea than me!
ANDREAS – This all sounds interesting. Just out of curiosity, where did you read about the koi person?

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#13. September 14th, 2010, at 5:04 PM.

Here is the link to the koi forum where i found the information. It’s in german – but maybe google translator can help you out. 😉

There are some really nice pictures in this koi-thread. Like the following pictures which very intersting because they show what the worms really eat (he “harvested” all the worms in this culture to please his kois and the pictures show how the gardens of the woorms looks after the gardeners (eaters) have gone to worm-heaven for a few days.)

My current experience with the inoculate method:
I had a box full of cardboard, zuccini and coffee and enough worm-tea to moisturise all the cardboard. I stired it up everytime i thought about it but at least everytime i put new coffee ground in the box. I worked on this box for about 3 days and put it in my vermiculture this morning. When i looked at it this afternoon i saw that quite a lot of the worms were already in this new layer. Maybe there were some other reasons for this but i am quite happy about the result. Maybe next time i will – in a somehow scientific way – prepare two boxes. One with worm-tea inauculation and one without.

ooops..sorry for the long post 🙂

Get your own gravatar by visiting Cianoy
#14. November 19th, 2010, at 1:32 AM.

Hi! I have a theory / question. I don’t have a lot of worms yet so my access to finished vermicompost is quite limited.

So I’m thinking….the main benefit of worm tea is the microbial content, right? What I did was to gather some, put it in an old stocking and just repeatedly dumped it in old water (just like Bentley).

However, I’ve been reusing the vermicompost to mix up other batches. It shouldn’t run out of microbes anyway, right?

I also figured the microbes should be in the worm bin too. So if I left he stocking overnight inside the bin, would it also manage to get microbes from the bin? I’m just imagining microbes jumping from one place to another.

Theories anyone? 😉

Get your own gravatar by visiting Bentley
#15. November 23rd, 2010, at 6:16 PM.

Very interesting question, Cianoy!
By repeatedly using the same vermicompost you would definitely lose some of the “ooomph”. Apart from microbes, there are also lots of beneficial compounds (humic acids etc etc) that provide vermicompost with much of its potency. As far as the microbes go (and don’t get me wrong – they ARE very important as well), I would think that as long as there were some, and as long as you were providing them with some good “food” in the tea brewer, I would think you could up the numbers sufficiently.
If vermicompost is in short supply, this might not be a bad strategy!

Get your own gravatar by visiting Rich
#16. September 6th, 2011, at 3:40 AM.

One of my big curiosities here is whether the Leachate from my dual-bin system would be okay to add in when I add my Molasses and other goodies?


Get your own gravatar by visiting Lola Ray
#17. January 6th, 2012, at 12:41 AM.

Just been vermicomposting a couple of weeks, but reading and reading–very interesting subject. Just getting into worm tea, and lots I don’t quite understand yet–some articles are very technical and some are basic. I liked this; simple and understandable instructions on making the tea. About the molasses–most of the articles I’ve read definitely say use it; the microbes or whatever slow down their activity if they don’t have the food. Can’t hurt. Don’t know how long it will take to get enough castings to make tea, but I will be reading! Just hope I don’t kill my worms first!

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#18. March 3rd, 2012, at 1:48 PM.

hi , thanks for useful your learning
how much a month we should use compost tea ?

Get your own gravatar by visiting kathy b.
#19. May 17th, 2012, at 6:54 PM.

Is Agave syrup considered a simple sugar?

Get your own gravatar by visiting ryazbeck
#20. May 29th, 2012, at 12:43 AM.

Thanks for the great info! Couple questions: How long do you have after aerating to use the tea in its best form? What if you continue to aerate it for longer periods of time (weeks or months) adding more compost and molasses periodically… will it sustain microbe growth or should you do it one batch at a time and use that batch right away?

Get your own gravatar by visiting clint mcivor
#21. June 4th, 2012, at 9:15 AM.

Instead of using muslin bags or pantyhose how about a circulating pump in the bottom of barrel that is able to grind castings at the same time as circulate through a garden hose returning 4 inches from the surface directed to push areation back down into barrel. Kinda like expresso


Get your own gravatar by visiting joe
#22. August 3rd, 2013, at 1:47 PM.

I have the exact same questions as RYAZBECK. I have been aerating for weeks at a time, thinking I had the same beneficial guys in the mixture. If I don’t have them, then I’ll make the tea and apply it sooner.

I did have the thought today that maybe I should feed the mixture again, so I added some more molasses. Please tell us your opinion on this matter.


Get your own gravatar by visiting Ken mitzel
#23. July 19th, 2014, at 4:02 PM.

Just a couple of quick questions:

1) does it benefit the tea more if I aerate longer? I have been aerating the current batch for about a week because I can’t use all in one spraying.
2) I see a lot of folks selling worm tea on the internet and wonder if it has any value to it if it’s past the recommended ‘use the first three days’ period. Are you getting ripped off?


Get your own gravatar by visiting Ken mitzel
#24. July 19th, 2014, at 4:13 PM.

Ok….sorry about the repetitive question about length of time aerating. I just read lots of good answers after posting.

Get your own gravatar by visiting Berta
#25. December 9th, 2015, at 3:17 PM.

I have an oxygen compressor/concentrator and yards of tubing. How would that be for aerating the castings water?

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