Coffee Grounds Vermicomposting – Fall Update

Back in the spring I wrote about the coffee grounds (pick-up) arrangement I had set up with a local coffee shop, and how I was using the grounds in my beds (see “Windrow Coffee Grounds Update“). I’m happy to report that the project has continued to hum along quite nicely thanks to the fairly modest amounts of material being produced (in comparison to my previous restaurant waste vermicomposting project). Aside from that, coffee grounds just generally tend to be a much easier material to deal with since they can be added basically anywhere, and you don’t need to worry about them getting too foul, attracting pests etc etc.

For the most part, all I’ve been doing is continuing to add layer upon layer of grounds onto my outdoor windrow beds (formerly known as “vermicomposting trenches“). In all honesty, I haven’t added much else to these beds (although there were certainly some deposits of food waste periodically throughout the summer). I thought for sure that the grounds were going to end up being a real challenge to deal with during the heat of the summer, especially once the serious drought hit – as I’ve written previously, coffee grounds seem to have a tendency to dry out really easily and then be difficult to re-wet.

As it turns out, the wet grounds ended up being very important for my beds – actually helping to ensure that there were moist zones down below where the worms were able to do ok. I must say that the cumulative benefits in terms of overall bed health have become readily apparent as well. The number of worms in beds now is very impressive!

There are a few factors that I think have made all the difference as compared to some of my previous coffee grounds trials. For one thing, these are used, wet grounds with lots of filters in them. Most of the grounds I experimented with previously were either unused or at least VERY dry, and contained no filters, so it took some effort to get them to the point of being “worm friendly”. These grounds I’ve been adding have also end up being exposed to the elements for quite some time, which really seems to make them even more appealing to the worms (although I’m surprised how quickly they can move into new deposits sometimes).

All in all, I am VERY pleased with the material, and feel very fortunate that I’ve been able to continue taking it from the coffee shop (and I imagine it’s nice for them not to worry about dealing with it too). This winter should be interesting! As per usual, I am planning to keep a stretch of bed protected from the elements, and hopefully with the regular addition of coffee grounds I’ll end up with my most successful winter system yet!
I’ll certainly keep everyone posted!

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    • John
    • October 15, 2011

    You should apply for a govenment grant to study the effects of caffiene on worms…The government has no qualms about handing out cash for studying the effects of bovine gas on the ozone layer. I think it’s high time that worms get their day in the spotlight;)

    • Nick
    • October 16, 2011

    Bentley, I have been reading your posts here and on vermicomoposters blogs etc etc,
    I “just” started up a vermicomposter (COW) I can get my hands on more then Enough ‘used’ coffee grinds since this is a small town I live in I know all the owners of the coffee shops/restaurants..

    Now my question is at this point in time I can only do indoor vermicomposting ( gets -40 here in northern bc )

    What is the best solution to composting of ucg in a small system like COW?

    • Steve K
    • October 17, 2011

    That’s a very interesting observation about the filters acting as bedding, in effect. I originally got into vermicomposting earlier this year (thanks again for your help, Bentley!), because I wanted to do something with all the coffee grounds we were throwing away at the time. Now, my worms get a diet of mostly old coffee, with fruit/veg/tea/egg shells in the minority, and they have been doing well.

    I tend to find what seem to be baby worms in the old coffee filters after they have been in the system for a while. I say “seem to be”, because they would be pot worms. However, they look a lot like smaller versions of the red worms and have a pale pinkish color, though they are almost transparent.

    As an aside, I would think that used coffee grounds would have a very low amount of caffeine in them, because caffeine is a water soluble compound.

    • jeanie
    • December 4, 2011

    This is a coffee grounds observation and question. When I spread a thin layer of used coffee grounds on the top of my worm bin, the grounds are covered with very tiny white/tannish shiny tear-drop shapes within a week or so, which I assumed are worm eggs. They do look like the worm egg pictures but also the mite pictures. They are only about 1 mm in diameter, do not get larger, do not appear to have legs, and disappear after not too long. I’ve never disturbed them, and never noticed any mites on the worms. Have you noticed that coffee grounds encourage the worms to reproduce rapidly?

    • Jennifer
    • April 4, 2014

    I have the same question as Jeanie. Was this situation covered on your site or elsewhere?

    • Mitch
    • November 24, 2015

    I am considering starting a coffee-grounds-only worm bin, but was worried that it would be bad to feed them only one kind of food. This article makes it sound like they might do fine with nothing but coffee grounds, as long as I make sure the bin doens’t overheat. Do you think so?

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