How Do I Know If Vermicompost Is Ready For Harvesting?

This email came from Ryan P:

Hi Bentley!

I have been a fan of your site for a while (recently joined e-mail list).

I have a question about harvesting the compost from my bins…. I have a feeling that it is time to harvest the compost from one of my bins – I grabbed out a couple big handfuls of material from the bin, placed it in little piles under a light and got the “little guys” (ENCs) back into their bin. The compost I got is wet and sticky — if I squeeze a handful 1-2 drops of water come out, then it is like a mud ball — is this normal? All the pictures I see online look soft and dry/crumbly.. If I let it dry out will it get crumbly, or have I done something wrong? … There is still quite a few pieces of corrugated cardboard throughout the bin (it was a big part of the bedding since I get a lot for free). Should I wait until they eat ALL the bedding materials before harvesting (or just pull it out when I harvest)?

Other than that I feel it is going very well (thanks to your site). I started with about 60 ENCs in a 12″x18″ bin, and now it is LOADED with them (and I have started a 2nd bin).

Hi Ryan,

Thanks for the kind words (I wrote “wormds” on my first try! lol). The good news is that “wet and sticky” vermicompost is very common, especially in any sort of enclosed plastic system. The beautiful, dry, crumbly stuff you see online has likely been: A) produced in a well-ventilated flow-through system, and/or B) allowed to sit (in well ventilated location) and dry/cure (more on this in a minute). It has also likely been screened!

The material I’ve been removing from from my VB48 and Worm Inn Mega systems recently fits that description for exactly those reasons (in the case of the ‘Mega’ vermicompost, I let it sit for a number days in an open tray and then screened it)! But most of the vermicompost I have harvested from plastic bins in the past has had more of a wet, gooey consistency. Now, that’s not to say that gooey is necessarily bad! Not at all.

I can still remember my very first vermicompost harvest (from the second bin I ever set up). I scooped the (rather muddy) stuff straight out of the bin and deposited it straight into the pot of a tropical plant I owned at the time. The plant grew like crazy after that – and I was definitely sold on the benefits of worm castings!

One important thing to mention about letting vermicompost sit and dry. It is VERY important that you mix/break it up on a regular basis during the drying process. If allowed to dry as a big solid clump, the material will be next to useless.

As for the unprocessed materials still in the bin – what you might try doing is stop feeding the worms for a couple of weeks. This allows them time (and gives them incentive) to process a lot of the left-overs in the system (assuming you have a decent population of worms in there). Whatever is not processed can either be removed before harvesting, or screened out (you can learn about a simple homemade screener design here: Super Simple Vermicompost Screener). This stuff is excellent “living material” that can be re-introduced to your system over time to help optimize the process.

Hope this helps!

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  1. Your post made me smile Bentley as I currently have about 4 kilos of muddy vermicompost from my smallish inverting bin drying in a tray. I recycle the unprocessed leftovers back into the bin while tossing any uncompostables such as peach and plum pits.

    As you mentioned the trick seems to be to mix up/stir the material and break up the lumps regularly while it’s drying.

    • GA
    • April 7, 2014

    Agree overall with everything mentioned here, but on ‘muddy/soggy/sticky’ probably means those clumps are too wet and hence need to dry out. My own experience with this is that once they dry out somewhat, actinomycetes move in looking like white fungus threads (but actually bacterial). For this bit, disturbing too much may actually slow the process a bit. To keep from clumping, a small bit of turning and a _small_ amount of water (like from a spray bottle) may be enough to keep it from turning into compost cement.

    I find the actinomycete phase (when the top layer gets obviously covered in white strands) plays an important role in breaking down otherwise-untouched (by worms) materials, especially cardboard, clumps of grass or other tough plants, wood particles, etc. But they need oxygen to do so, and time, as in curing. Worms that remain are not harmed and hang around beneath the surface and find stuff to eat.

    When this curing process is let to run its course, first there is a fantastic RICH mushroom smell, and then a very strong earthy smell that we all associate with great compost.

    • GA
    • April 7, 2014

    Whoops, didn’t have enough coffee when I wrote that.

    I meant to mention a few things here:
    -I’ve found that clumps that dry out can be easily crumbled by hand, then lightly sprayed with water.
    -The air aspect is critical – worms only do part of the composting, and oxygen is the key part that lets other compost organisms do their work.

    • Brandi Solis
    • May 1, 2014

    I have started a farm with my 4th grade class (inner city, Sacramento). We are loving and learning with our hands on science! Especially things about our worms as animals, ecosystem, and composting cycle. Thank you for all your helpful information!

    My question has to do with fruit flies (or white flies) that have also moved into our habitat. This is a bit distracting in our classroom and we were wondering what to do to in order to get rid of the nats and prevent them from returning. We are using a “Can O Worms” 3 tier plastic bin.

    Thank you!
    Brandi Solis

    • Vickie
    • May 6, 2015

    I’m so glad someone has already asked this question! I just switched an older worm farm to the Worm Farm 360. My older model Worm Farm had a crack in the base and liquid was leaking. I’m fairly close to harvesting my first tray of vemicompost. I split the bottom (finishing tray ) a few weeks ago to start the second Worm Farm 360.

    When I checked earlier it seemed that the finishing tray was gooey wet. I am a little overprotective of my new worms. I had the old worm farm in operation for probably 4 years. I had it in the garage last year and apparently exhaust/chemicals from the resident mechanic got the best of them.

    I’m getting very excited! I have a nice little container garden on the deck waiting for the vermicompost. I’m growing vegetables not just for myself but for my 7 month old grandson to nom nom on!!

    Currently have one finishing tray and 3-4 working trays. I’m feeding the second Worm Farm slowly since there aren’t as many worms as in the first. My husband is very afraid that I may have a worm addiction! hahahahaha

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