Growing Worms vs Breeding Worms vs Waste Processing

Some interesting questions from Chad:

Hi Bentley,

I was inspired by your blog to start vermicomposting and have been doing it for over a year, ever since I DIYed my own flow-through system.

I have two questions:
How can I create optimal conditions for different situations:

1. Vermiculture, or optimizing worm (re)production.
2. Vermicomposting, or optimizing vermicompost/casting output.
3. Biomass, or optimizing to inrease worm size.

My second question:
My output looks much like traditional compost, kind of a “rich mixture” of material, but how do I get pure castings? Feed it through the system again?

Thanks for all your help, and keep up the good work.

Hi Chad,
While there is certainly some overlap, you are correct to assume that there are specific strategies best suited to each of these. Unfortunately, this is one of those topics that could literally be turned into a book, but let me see if I can at least provide you with some guidelines here.

1) Vermiculture – There are a variety of things you can do to encourage worms to reproduce more. Probably the best overall gameplan is to cater to their natural instincts. Remember that these worms are adapted for life in an often-rapidly-changing environment (eg. a small manure heap that can dry out during the summer and freeze solid during the winter), so they tend to respond pretty quickly to various natural cues. For example, if you start with a smaller number of worms in a larger system they are much more likely to increase in number (so as to take advantage of available resources as fast as they can) than if they are in an overcrowded system.

Changes in temperature and moisture content can also have an impact on reproduction. Not too surprisingly (when considering their natural environment), Red Worms tend to reproduce more at cooler temperatures. This makes sense since it’s an effective strategy for ensuring that there are more cocoons as winter approaches (they are better adapted for the cold than the worms themselves), and a rapid recolonization of the habitat as things warm up in the spring. Similarly, as Red Worm habitat dries out there will be a greater tendency for the worms to drop cocoons since this will help to ensure the survival of the population – even if the worms end up dying, it’s likely that many of the cocoons will still hatch out once conditions become more favorable.

One other strategy I’ve found to work well for encouraging the release of cocoons is adding certain type of materials to your worm bin/bed. A prime example – and one that will be very applicable for most home vermicomposters – is the use of lots of shredded cardboard and/or other paper products as bedding materials. There is actual academic research that has demonstrated this (unfortunately, I don’t have time to track down the reference), and even a small study of my own (while a university student) seemed to support this. Off hand, I can’t remember the exact figures, but as I recall we found something like double the number of cocoons in a bin containing paper pulp as the primary bedding as we did in the next closest treatment (which was aged manure I believe). Other materials, such as burlap, seem to encourage cocoon dropping as well – some believe (in both these cases) that this has something to do with providing the worms with a physical structure that can help them get their clitellar band (which becomes the cocoon) off.

Before moving on, it’s important to point out that there is a big difference between getting your worm to reproduce and lay loads of cocoons, and ending up with a large, thriving worm population. Don’t forget that once you DO have an abundance of cocoons you should create an environment that’s optimized for worm hatching and growth (good moisture content, warm temperatures, food source etc)!

2) Vermicomposting – if your aim is primarily to process lots of waste materials, having lots of worms right off the bat will certainly be a good start. You will also want to work hard to maintain optimal conditions for the worms, and for the processing of the materials in general. Open – or at least, very well ventilated systems are a must since everything will slow down a great deal as oxygen levels drop. Similarly, you’ll need to maintain warm (but not overly “hot” temperatures) – ideally somewhere between 70 and 86F (~21 and 30C). Cooler temps will also greatly slow down the vermicomposting process.

Moisture content of the waste materials – while certainly important for the health of the worms – will need to be kept in check since a wet environment will have a far greater tendency to become anaerobic. It’s also extremely important for the waste materials to be “optimized” for rapid microbial colonization and/or consumption by the worms. Bulky, resistant materials should be chopped up as much as possible, and fresh manures should be precomposted (and potentially broken down further if overly bulky). Ideally, your waste mix should also have a C:N in the vicinity of 25:1.

If you want to produce consistent, high quality castings (to sell, for example) – naturally, you will want to keep the process (temp, moisture, oxygen levels, system used etc etc) and feedstock as consistent as possible.

3) Growing Big Worms – there are several important factors to keep in mind here: 1) worm density, 2) moisture content, and 3) overall nutrition. When there are fewer worms in a given system (i.e. less competition for resources), the worms will have the tendency to get bigger, so one simple strategy is to keep moving worms from your main beds into new beds (with lower worm densities) as they become mature. Of course, this won’t really help all that much if the new systems are very dry and/or don’t contain rich food materials.

Worms are basically just bags of water, so one easy way to keep them looking “juicy” is to make sure they are living in a fairly moist environment – since we’re way more concerned about their size than the speed at which they are consuming their food, it won’t be quite so important to keep things as well oxygenated as in the waste-processing (castings-producing) systems. Of course, that’s definitely not to say you should let their habitat become foul and anaerobic.

N-rich foods such as farmyard manure, and/or specialized feeds like “worm chow” (yes, it does indeed exist) are great for helping you grow larger worms. Seasoned worm farming pros even have their own “secret formulas” for creating the “perfect” food mix – but getting them to share them with you might take some convincing!

One other quick thing to mention about worm food – there have been studies to show that particle size can have a significant impact on worm growth – with smaller particle size having been found to be much more beneficial than larger particle size. This is certainly something worth keeping in mind – but, as always, make sure you keep the important principles of vermicomposting (namely those relating to worm health) in mind as well! Too much nitrogen (low C:N) can result in the release of ammonia gas, which is very toxic to worms at low concentrations. Materials that are too finely ground up can result in a lack of air flow, which leads to a variety of problems.

As for your second question…

In all honesty, achieving 100% pure castings is pretty darn difficult – since you would have to make sure that every single particle of material has passed through a worm. This is simply NOT going to happen in most cases, especially if you are using a somewhat heterogeneous food mix. Letting the material run through your beds a couple of times would certainly help, as would screening – but you should almost always expect to have at least a small percentage of “other” – non-worm-poop – materials in your finished product. This is why it’s actually a bit more accurate to use the term “vermicompost” rather than “worm castings” (but don’t feel bad – I use them interchangeably, as do many others).

Anyway- I hope this helps!

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  1. You mention “smaller particle size.” Are you referring just to worm food or suggesting that generally if we chop food waste more finely before putting it into the worm/compost container, that’ll be helpful?
    btw, we have great worm population in several plastic containers (e.g. a big plastic garbage can in which I drilled a lot of holes) in southern New Mexico, where they survived difficult winter and are surviving scorching summer as well — so far.

    • Bentley
    • July 26, 2012

    Hi Peter – the research refers to particle size of food materials (improving growth). There are other factors to consider, however – for example, smaller particles can lead to decreased air flow, especially when the food materials are water-rich. SO, while it’s certainly beneficial to chop your waste materials really finely (or blend them etc), just make sure you offset these deposits by adding some bulky, absorbent bedding materials as well.
    Congrats on the success with the plastic bins! Just goes to show that you never can tell how tough these worms are going to be! I’d certainly be worried about keeping worms in a plastic bin outside during a “scorching summer” (and “difficult winter”). That’s cool!

    • pj
    • July 30, 2012

    I am very interested in starting to raise worms for fishing. Is it hard to raise small earthworms in plastic containers. Thanks for your information.

    • Bentley
    • August 2, 2012

    Hi PJ,
    It is very easy to raise “small” composting worms in plastic containers, but I’m not sure small worms would be ideal for fishing (unless you are mostly focused on trout and/or panfish). Some of the advice given above should help you grow larger worms though.

    • JOHN G.
    • August 4, 2012

    Hi Peter

    I raise red worm’s for fish bait ,there’s a product called cricket food that really make’s them fat .You can most likely find it at any feed store,hope this help’s.

    • erica
    • August 6, 2012


    • K. L. Zimmerman
    • August 7, 2012

    I have recently started using a medium called coir (which is from the coconut husk) I am presently mixing it about 1/3 ratio to commercialized composted cow manure. I then mix in a handful of worm chow to a 4 gallon bucket. Would it be better to layer the bottom of my buckets with this product rather than mixing it in? I have been raising Africans and red wigglers (not mixed) for about 4 years and have had absolutely no luck with getting the worms to be any size. I have over 100 open buckets with a piece of plywood over them to keep the light out and 4 (1 inch holes in the bottom of each bucket. Approximately how many worms should be in each bucket to provide maximum size? Great blog!!!

    • docboggle
    • July 3, 2013

    I’ve found a good way of keeping the heat off of my outdoor worm farm [ consisting of a couple of nested 32 gallon plastic trash cans, $13 ea from Menards, inner one with 1/2″ holes drilled in the bottom / sides, outer one intact ] during the scorching Missouri Summers is to not only keep them in a shady area of the yard, but also dig a small pit in the earth so that the trash cans are about half way in the ground.

    So far, so good!

    • Tana
    • June 12, 2014

    Hi, I am thinking on making a small compost bin/worm farm in my own backyard. We have a plastic container about 1 1/2 – 2 feet tall, with a wide open top. We own a horse who produces TONS of manure, and have lots of scraps none of our animals enjoy.

    Would horse manure and scraps be enough to successfully produce a cycling farm? I’d cull out every now and then larger worms through feeding them to my chickens and fishing with them in order to keep the population at a correct size, and would water the bin every day or so depending on need and would probably change to fresh manure on a weekly/bi-weekly bases, depending on the need.

    • Aubrey
    • August 8, 2014

    I have been reading this site for months and after some experimenting of my own, mostly thanks to suggestions from this site, I finally have a system. I have what I call a “home bin” which is a 29 gallon RubberMaid bin, and I have “breeding bins” which are 10 gallons. I put the adults in the breeding bin (the ones with the band near their heads), about 1.25 lbs per bin. For water content, I over water, I don’t have drain holes in the bottom, but I have found that by slightly over watering and having water pool on the bottom, it creates several layers of different moisture levels, then the worms choose which level they want to be on. Also I only do this when I first put them in the bin, I have air holes around the top which seems to be enough, and I keep the lid on. I never have to mess with the water level, and I use worm chow and just put it on the top of the bedding, when it’s gone, I add more. I sort these bins once a week, or two depending on how much has turned to compost. I put the adults in a new bin, the “bedding” in another bin, screen the bedding with 1/4 inch screen, then set a new bin for the next sorting session. With the compost which still has a ton of bedding at this point, I screen it with 1/8 inch screen. Then I pick out as many cocoons as I can and put them in the “home bin” to hatch, that bin is gone through once every 2 months or so depending on population, and maybe start another breeding bin if I have enough adults. The worms in the breeding bin are HUGE, at least 6 inches long sometimes a little longer and almost as thick as my pinky. I’ve only been doing this for a month, so I can’t wait to see if they keep growing. Every time I look they are bigger. Their cocoon production is pretty decent too, at least 50 cocoons each sorting. I have to say, I got the breeding bin idea from Bentley, and it was a great idea! Thanks so much for this site and all of the advise Bentley, you and all of the people who read and comment on your site are great and have really helped me.

    • Aubrey
    • August 11, 2014

    I wanted to clarify in my previous post. The worms I am currently working the breeding bins with are ENCs. I don’t have enough adult Reds or ANCs to work with, but as soon as I do I will be using the same set up with them as well.

    • Amol
    • February 9, 2015


    We have a cow farm with 40 cows and getting around 500kgs of cow dung daily. We are planning to start vermicomposting using cow dung. Could you please guide us since we are new into this field.

    • blinp
    • March 23, 2019

    whats better, a small but wide container or a wide and deep one? is depth or with more important for worms?

    • Bentley
    • March 29, 2019

    Hi Blinp
    Great question. Surface area is really important since it helps with air flow. Deep bins with little surface area (eg garbage cans) tend not to work nearly as well as something like a big Rubbermaid bin that’s 12-18″ deep. With plenty of air holes, nearly anything can work – you just need to find the right balance (too much air can lead to drying out, which is also not ideal). Hope this helps

    • Bryce G. Carswell
    • May 24, 2020

    Has anyone used ground up lentil beans for a worm chow? I mixed them with rolled oats and blended to a semi fine flour. I plan on adding some partially composted horse bedding/manure and mixing with a spoonful of molasses. What do you think?

    • Bentley
    • May 28, 2020

    I have definitely thought about the use of legumes – and I have used the syrup from salt-free (important!) canned beans to soak cardboard. I think lentils would be fantastic and your mix in general sounds like it would work well. Just a question of costs .

    • Julie
    • October 10, 2021

    I have quite a lot of legumes which may be stale and Iā€™m considering making worm feed. Would it be best to cook them first before feeding to worms? Perhaps freeze and thaw, too? Some beans, like kidney beans, are toxic for humans to consume if not adequately cooked. Are all legumes safe for red wigglers, uncooked and ground? Thanks, Bentley.

    • Bentley
    • October 22, 2021

    Hi Julie,
    I would think cooking them first wouuld definitely help (would likely take a fair bit longer to break down otherwise) – but maybe even soaking them in water for a number of days would be enough? As toxicity, other that really harsh compounds that could harm the worms even via contact (eg capsaicin in hot peppers), and persistent man-made toxins, my hunch is that toxins in plants will get broken down by microbes and should pose little or no threat to the worms. I’d be careful about amounts of legumes added, though, since they are N-rich but also starchy so there is definitely some potential for them getting pretty foul if a lot added at once.

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