Windrow Coffee Grounds Update

Just wanted to post a quick update for my continuing outdoor-coffee-grounds-vermicomposting efforts. As mentioned a few times, I’ve been receiving grounds from a local “fair trade” coffee shop here in town, and the arrangement has provided me with a good opportunity to “play” with this material.

In the past, I’ve run into issues with grounds when adding them in concentrated zones in outdoor beds. They seem to over-heat and dry out quite readily. The key has always been to keep them nice and moist, and basically just to let them sit. Any time I’ve found decent numbers of worms in coffee grounds (outside) it’s been in older, wet material.

This spring I’ve been trying something a little different. I’ve been combining coffee grounds with well-aged (and heavily bedded) horse manure. This is a material that holds water well, and worms go crazy for it by itself, so in some ways you might say I’m “cheating” a bit here – haha! I should point out, though, that while the two materials are in the same beds, I am not (yet) actively mixing them all that much. Generally, I’ve been layering the grounds underneath a thick cover of aged manure in a effort to keep them wet. I’ve also been making an effort to keep the grounds in relatively shallow layers.

The one concern I had with this approach was that the beds would get too warm, but given how incredibly cold this spring has been (by typical standards), the additional warmth in the beds has actually been appreciated. We shall see how things pan out once the warmer weather arrives, though!

So far so good! I’m finding lots of worms in zones that have lots of grounds, and for the most part the grounds seem to be staying quite moist (fairly wet weather as of late has helped I’m sure). I am definitely starting to appreciate this material more and more!

As mentioned in my last post, I have plans to construct my own compost tumbler sometime this spring (hopefully in the next 2-3 weeks), and one thing I really want to test out is mixing and “pre-composting” coffee grounds with other materials to see if that makes them even more appealing to the worms.

Should be fun!

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    • Tom Crabill
    • April 28, 2011

    I like to mix coffee grounds with crushed egg shells & apply to the top of the bin. The calcium in the shells offsets the acidic grounds. I’ve never heard of anyone else doing that, so it’s probably not necessary. I suspect the acidity in coffee grounds isn’t a problem unless you add them to bedding that’s already acidic (like old bedding that needs changing).

  1. When i get the chance,i’ll do a few more experiments with coffee grounds.All i know is the one way i’m doing it is working good.But now i have to test the type worms that like it.I know PE worms do.But i’ll have to do a controlled test.Maybe some type worms like it a lot more done in different ways?

    • Count of Anjou
    • April 29, 2011

    My foray into vermicomposting after 5 years of hot composting horse manure is proceeding too slowly for me. About two weeks ago, a coworker let me adopt a handful of her Eisenia foetida for a 28-gallon worm bin I was making. To the bin I added, to wit, two boxes of shredded ofice paper, a box of shredded newspaper, and a shredded pizza box. For food, I then placed 3 gallons of hot composted horse manure in two of the corners of the bin and a gallon of miscellaneous kitchen scraps in each of the other two corners. I then wetted it all down with about 5 gallons of well water. It’s going to take those 50 Eisenia foetida forever (a year?) to work over all that. In the interim, I am chomping at the bit. I want to buy 5 pounds of Eisenia hortensis and intoduce them to my hot compost pile, but it’s still running too hot (120°F) after 6 months. It’s going to be interesting to see what 5 pounds of the Eisenia hortensis can do to 850 cubic feet of composted manure after 6 months.

  2. My personal Eisenia hortensis population doesn’t like horse manure like other worms do.As was noted in more than one scientific study.Maybe someone else had more luck at it than me?But they aren’t my first choice for horse manure.This is just what i personally noted as compared to Eisenia fetida/andrei.My Eisenia hortensis seemed to like the cardboard a lot better.So i personally use them for paper products.
    Also not sure of your location?But they also die a lot easier than other worms from heat problems.

    • Count of Anjou
    • May 2, 2011

    Larry, I don’t have much choice in worm selection being that the horse manure/bedding hot compost is only going to be cool enough to support any worms for about 6 months out of the year (late Spring to lat Fall). During the other half of the year, the compost is actively cooking at 140-160°F (to kill the weed seeds). Also, once per year (early Winter), the entire pile gets harvested to make room for the next batch. This means that the worms are going to need to move elsewhere. The only composting worms that can survive in native soil are Eisenia hortensis. I guess I could move the worms into an indoor bin, but I’m not sure a 28 gallon bin would hold them all after feasting on 850 cubic feet of compost for 6 months. Plus, I was really interested in the Eisenia hortensis because I want to transplant the excess to my raised garden beds… well, except for those I want to feed to the chickens. Incidentally, my 7 acre farmstead is in a cool weather temperate zone (Northeastern US). I suspect I will never have enough compost or worms for my needs and my neighbors will never cease to be amazed by my insatiable desire for these. They can’t refrain from asking me every year what I am going to do with all that manure (from their 11 horses). Of course, people also can’t fathom why I am using unmedicated chick starter as a substitute for commercial (clay) cat litter. The answer is it’s cheaper ($24 per 100 pounds), environmentally friendly, and compostable (biodegradable).

  3. I gotcha Count of Anjou! Any way of doing some type windrow in the shape of a o with a small gap?You can hot compost more than one pile to kill seeds.Then throw it on the one end so the worms feed forward.You could harvest large sections of the finished product and even run it through a trommel.Then the big stuff just throw back where the worms are feeding.Wish i had more room.But all i got is a 1/4 acre.And my house takes up part of that darn it! LOL!Also i have EF and EH in my raised garden beds.But i have a organic media.No sand in one.The others i will eventually change over to the same thing.And you can put a little food for the worms in there if you are not putting in horse manure or other stuff.My bed even has cardboard in it in small amounts.Also the cocoons from the vc will hatch out and you may have more worms in there than you imagine.

    • Chris
    • May 6, 2011

    I also top coffee grounds with egg shells to counter the acidity. I’m not sure if that works, but I’ve gotten used to doing it

    • Count of Anjou
    • May 6, 2011


    If the analyses conducted by Starbucks on their “Grouds for your Garden” are any indication, the pH of the spent coffee grounds is a tad shy of neutral (pH = 6.9). That’s not really acidic, so I would think that countering the acidity is not necessary. Of course, acidity is relative, so if you live in the Southwestern US, where the soil is highly alkaline (pH>7), then the coffee grounds would be considerably more acidic, albeit in a beneficial way as many plants prefer slightly acidic pH levels.

    • Dynamind
    • June 24, 2011

    I make very good experiences with a mixture of straw (moistened with “wormtea” ) and coffee ground. I “precompost'” this outside the bin for about a week or two. The worms love to surf around in this stuff and it is transforming into vermicompost very fast. But it happens inside a Can-O-Worm bin and drying out is not really a problem.

    • rap
    • July 27, 2011

    I love this site and all it’s contributor’s ideas, solutions, experiments….
    just wanted to mention to be cautious with the crushed eggshells against the delicate worm bodies.

    I too used to grind up the egg shells like tiny grains of sand and add it to the bin.

    I never thought of how it might offset the acidic coffee grinds. Great pointer.

    • Adam
    • August 7, 2012

    @tom Crabill from what I’ve researched on used coffee grounds, they aren’t too acidic at all. What I’ve read states between 6.4-6.9 PH, which doesn’t seem to be too concerning to me.

    • Tim
    • April 15, 2014

    I have a 3 feet by 20 inches by 6 inches deep container of red wigglers compost. We make about 6 cups of coffee each morning. How much of the coffee/filters should I put in my worm bin (like one a day, one a week or what would be good)?

    • Adam
    • April 16, 2014

    I’m not sure I’m following Count. It sounds like you are wanting European Nightcrawlers to compost your manure, then move to your soil when they are done? Does your soil have complete shade and lots of organic matter? They are composting worms so they may not survive in just your soil. Alabama Jumpers may be a better option.

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