How Do I Know If My Vermicompost is Ready to Harvest?

A common vermicomposting conundrum is how to recognize when your vermicompost is finished and ready to harvest your worm castings.  This is a tough question, especially if you don’t have a system like the Urban Worm Bag, the Urban Worm Company’s own worm bin which allows you empty the finished contents from below, where worm castings will tend to settle.

The question gets tougher when you are shifting the goal posts by continuing to add new food (and hopefully bedding.)  This ensures your vermicompost is never really “finished.”

Let’s say you started vermicomposting a few months ago, didn’t kill your worms a couple times like I did, and have been diligently recycling your food scraps into black gold for your garden.

Sweet!

What should you be looking for to decide now is the time to harvest?

5 Signs Your Vermicompost is Finished and Ready to Harvest

Deep, Dark Brown Color

The majority of your vermicompost has that deep, rich color.  While we like to refer to finished compost – both of the thermophilic and worm-related varieties – as “black gold,” an actual black color may indicate your vermicompost is well beyond finished and is now possibly anaerobic.  Note: If your worms are fed a steady diet of coffee grounds, this may not apply.

Uniform Texture

Vermicompost that needs to be harvested will have a uniform texture throughout.  However, if you’re the type who grinds your food and bedding together to optimize for faster processing, this may not be the best indicator for you.

Worm Reproduction Slows

As you can imagine, crapping the bed won’t help put your partner in the mood.  Granted, worms may have a greater tolerance for staying amorous in their own doody, but everyone’s got their limits.  Expect to see fewer cocoons in mature vermicompost.

Small Worm Size

The worms themselves are excellent indicators of a bin that needs to be changed out for fresh bedding and food.  Not only will reproduction slow, but the actual biomass of each worm will shrink to reflect inadequate conditions for growth and reproduction.

Flat, Felt-Like Surface

Thanks to Brian Donaldson for using the term “felted” because I had been struggling with a word to describe it.  A top layer of vermicompost that has the appearance of black or brown billiards table indicates the bin is ready to be fed, fluffed, or changed altogether.

What If I Have Several of the Above?

If you’re seeing at 2-3 of the indicators above, it’s probably time to consider harvesting the worm castings.  In fact, it’s likely your vermicompost is already past its peak microbial population.

This post discusses the various methods of harvesting worm castings and discusses whether you should even bother separating the fine vermicompost from the coarser material in your worm bin.

While simply piling more bedding and food is the easiest way to prolong the tedious task of separating your worms from their castings, it’s a good habit to get some practice using the light method of harvesting or harvest small amounts of castings using a makeshift harvester I designed.

Another easier option for harvesting is to simply feed one side of the bin, wait a few days, then scoop out the finished vermicompost from the other side.

But my most recommended method is moving your bin over to the Urban Worm Bag, a pretty nifty product that allows you to harvest your castings from the bottom by simply opening a zipper.  The breathable fabric that makes up this worm bin allows for excellent moisture control.  It’s about as close to a continuous flow digester as you can get without spending thousands of dollars.

Were there any indicators of mature vermicompost that I missed?  Let me know in the comments below.  I’ll update the list as necessary and give you credit!

18 thoughts on “How Do I Know If My Vermicompost is Ready to Harvest?

  1. light brown wet worm compost that isn’t stinky. A problem? Submitted again because I didn’t check the box for follow up comments to be sent to me.

    1. Hi Carol,
      Sorry it took me awhile to get back to you! I think your castings ought to be a dark brown color. And they should NEVER stink at all. What is your bedding and food source?

  2. Thank you. This is very comprehensive. I have a small bin, add lots of coffee grounds, and I grind the food I add, so my bin always looked dark and homogeneous, so I’ve been wondering how I would be able to tell when it would be ready. I did notice fewer cocoons recently. So, I am guessing it’s time!

  3. Well I’ve probably messed up I started vermicopostimd fec26 last year I started with 1000 uncle Jim’s red wiggles in a 17 gallon tote, I now have 4 17 gallon totes and I’ve not harvested any compost! I don’t know how to get the worms out
    To harvest but they have multiplied very good I get thier food out of grocery store dumdters and I run everything my worms eat through a food processor and then freeze it for later use, I also have a restaurant that gives me all the eggshell and coffee grounds I need have I wasted my compost or what should I do now??

      1. Thanks Steve I now have 10 totes and a hell a lot of worms lol is there a way to slow them down lol I’ve got a lot of worm castings as well my totes have never smelled I feed them processed food through my $20 food processor and give them coffee grounds every feeding which is once a week things are going very good thanks for all ur help….Jerry J

  4. I wasn’t too familiar with the way a worm bins supposed to be set up and just have a single container with ventilation holes card board and veggie scraps I think there’s about 50 of em in there and they don’t seem too bummed out or dead surprisingly . But it’s prolly been a month or so since they were in there. can I just put them in a new bin after I put the bedding in ? Or do I have to pick em out separately to transfer them ? They prolly have planned an attack on me by now 😳

    1. It’s been a couple months so don’t know if you’ll see this or if your question has already been answered. What size is your bin. 50 is small population and a month isn’t a whole lot of time. But good news! I’m new to this as well and like you started with a small number (100 or less, though I kept adding more when I could) an with the same set up as you in a single 15 gallon tote (I have two now and getting ready to move on to a third or if time permits diy upgrade). Have you not seen your worms? What kind are you using? I started with hortensis (European night crawler) and they seem to burrow deeper than the standard red wrigglers (I have some with the hortensis in one of my bins now, and seem to me to be great partners). You might not be seeing your worms if you have a decent sized bin like me because they’re just hidden. I was blown away how many I had the first time I changed the bedding. Also, I don’t know that there would be a very noticeable increase in popultion dyer only one month. I believe population is supposed to double every 6 months or so. Also, there’s a great vermicomposting group on Facebook. And just for encouragement: I neglected my first bin for 2 months and didn’t kill my worms. They were haggard and hungry, the bin consisting of only them and their poo, but so long as they get enough food but not too much, same with water, and the temp is pleasant, you’ll be fine. They’re tough critters. Hoped this helped

  5. I have a Tupperware bin that is ready to harvest. However, it has so much bedding in it still, which disguised the finished compost between the middle and bottom of the bin. I added a small amount of food on one side so the worms can migrate, but they are not. Each time I’ve been feeding the last few weeks (once a week), that area becomes warm/hot to the touch (not burning hot) every time.
    In the beginning of this bin, the food never became warm/hot. So, I’m not understanding why it is now with every feeding. Can you help explain why the the immediate area I place the food along with additional bedding becomes hot? I noticed the worms don’t really hang around it when it is, so the scraps tend to just decompose. Also, I freeze my scraps first. My bin is just right moisture wise. Has pleasant earthy smell.

    1. Hey Jennifer. It is likely becoming hot from the microbial action. Just like in a thermophilic compost pile, when nitrogenous material is mixed with carbonaceous material it increases the activities of bacteria and fungi which creates heat.

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