Vermicomposting Weeds – Revisited

(Lots of comfrey growing in various corners of my yard – time to put it to good use!)

Adding green wastes to a home worm bin isn’t something I typically recommend – especially not to those just getting started. Materials like grass clippings and garden weeds tend to require more pre-processing (so as to make them worm-friendly) than most of the usual kitchen scraps , and when they break down they can release ammonia gas (which – as frequently mentioned – is very toxic for worms). Of course, this hasn’t stopped me from using these materials a fair bit in my own systems – and writing about it here.

Here are some examples…

Comfrey and Banana Peels?
Worm Inn Journal-06-22-12 (vermicomposting weeds in a Worm Inn)
Can worms live on grass clippings alone?

Comfrey is a plant I have a particular interest in A) because it is well-known as a “dynamic accumulator” (aka “nutrient miner”, and B) because I happen to have a lot of it growing in various parts of the yard. Unlike many other “weeds” it also seems to break down really quickly in a composting environment.

My recently-renewed interest in vermicomposting comfrey (and other green wastes) actually developed rather accidentally. On a whim I had tossed – into a fairly new plastic worm bin – a big handful of comfrey leaves straight from the garden. I can’t even recall what my motivation had been – I guess I just basically wanted to “see what would happen” (that seems to be my motivation a LOT of the time! lol). Another motivator for using something other than fruit and veggie scraps at this time of year is the seemingly-unavoidable appearance of fruit flies around the house. As much as I love “playing” with fruit (and other) fly infestations – and writing about it here, it’s sometimes nice just to keep things under control!

Anyway, getting back to what I was saying…once I added the leaves, I closed up the bin and then basically forgot about it for a couple of weeks (another common practice of mine – lol). When I finally did remember to check on it last Friday, I was quite surprised to find almost no trace of the leaves other than some remnants of the thick stalks and veins.

Here are the “Before” and “After” shots:

Now, I realize 2 weeks is not exactly “overnight” – lol – but considering how resistant these sorts of fresh plant materials can be (in comparison to a lot of food wastes), and the fact that I did absolutely nothing to “optimize” the leaves for vermicomposting, it’s still pretty impressive.

Given these positive results, and the fact that I have loads of green materials available at this time of year, I decided to take things a bit further with my experimentation. I collected a second, larger batch of comfrey leaves (along with various other weeds) for my plastic bin system. But unlike the first time, I decided to chop it up and moisten it before adding it to the bin.

This was done last Friday. Today – just shy of 1 week later, this is what the plant material looks like:

There are lots of worms in the habitat zone just below, and based on the volume reduction I’d say they are definitely consuming the material. My guess is that, unlike last time, it will be mostly gone within a few days (so just over 1 week total time).

Now that I’ve got “weeds on the brain” (hmmm…good thing I didn’t forget the “s” – lol), I’ve also decided to dedicate my next Worm Inn Mega system (once set up – hopefully soon) 100% to green waste vermicomposting. Once my safe habitat zone has been established, I will aim to add only comfrey, various other yard weeds, and grass clippings. No bedding, no “living material” – nuthin but weeds!

My gut feeling is that the plants will provide enough resistant, fibrous material to offer the worms a livable habitat without the need for shredded cardboard etc. But let me emphasize again the fact that I WILL be creating a safe habitat zone (in my usual manner) before the onslaught of weeds.

As always…it should be fun!
Stay tuned.


As touched on earlier, if you are fairly new to vermicomposting I do NOT recommend using any sort of green waste in a typical small to medium sized enclosed plastic worm bin. For those who are determined to test the weedy waters – MAKE SURE your bin has excellent ventilation (notice in my pictures that my air holes are nearly an inch across), and make sure you leave the material up top. Don’t mix it in. One other caution is to make sure you NEVER use green wastes that have been sprayed with any form of pesticide.

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  1. Seems like your pushing the envelope so to speak as always Bently. By the way how good is your ventilation? I could see some problems in the future if it isn’t good enough. I wonder how much a worm inn would process of this stuff if it was optimized and such.

    • John W.
    • July 11, 2014

    I use grass clippings all the time. I let them sit out in the yard for a few days or even longer so that they start to break down and then just dump them on top of my worm inn. The best is when the mulched grass collects under my mower and I have to scrape off the clippings. The worms are in that stuff within hours. I don’t dump it in large quantities right away, but if its been in a pile for a few days, but before it gets brown…works great for me. I don’t think I would try it in a plastic bin though. I know my worms have plenty of place to dig down if I made a mistake.

    • Paul from Winnipeg
    • July 13, 2014

    I tried this in the spring of this year. I was clearing out perennial weeds from a flower garden and ended up with two gallons of chopped up weed tops and mostly roots. Poured it into my worm inn and hoped I hadn’t just made a big mistake. ha ha. The worms ended up doing a great job of processing that material. I had the odd dandelion appear, so I chopped up the offender and the worms finished it off. Haven’t tried grass clippings yet.

    • GA
    • July 18, 2014

    I have done this with all kinds many times. Given enough time, they will break down and be eaten like most other things.

    That said, some experience:
    1) The biggest issue with yard wastes is volume. Most people get enough weeds and grass to make it easy to overdo it, and yard waste will tend to compact very quickly and then not enough air, stinky and slow in further composting. (This is true with or without worms). Lots of different ways to deal with it, including turning, but best is to just be careful about adding too much at once.

    2) Grass clippings can be really prone to compacting/going anaerobic. My theory is that this is where they got the term ‘green manure’ – compacted wet grass clippings can be indistinguishable (esp smell!) from cow manure. Except that it breaks down more slowly. Once this happens, that grass stuff ends up being very tough, and really only getting enough air and letting it dry out will work. On the plus side, worms seem quite happy to live in the stinky mess.

    3) Final thought is why? I do put a fair amount of yard waste through bins, especially leaves in fall, but mulched yard waste,esp green, is best left in the yard where it breaks down and disappears pretty quickly. This is (in my view) the best way to deal with both the volume issue and esp grass clippings – they disappear on their own quite quickly. Then what’s left – the odds and ends, weeds you don’t want laying about etc – can be handled more easily in compost bins (worms or no).

    There are always some more fibrous wastes (stems, etc) that take longer but as you put it Bentley they provide some ‘structure’ (analogous to cardboard) to keep air moving.

    I also toss in bark and other woody wastes, esp when they’re not large, and they break down as well. Always some bits that don’t, or very slowly, but that doesn’t bother me.

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