Worm Bed Surface Area

Here’s a question from Al:

Love your site. Now to the meat…

You mentioned that “…surface area is
far more important than depth…”. And
thus bins are better than buckets.

Under optimal conditions, what would the
density of worms (E. fetida) be per square
foot of “bin top”? In other words, how
many worms, under ideal conditions, would
be feeding on a square foot of food?

Really appreciate your site. Thank you.

Al

Hi Al,
This is an interesting topic of discussion for sure. Thanks for bringing it up.
You mentioned E. fetida (Red Worms) so I know you are referring specifically to them, but I DO want to emphasize (for other people’s benefit) that depth is a bit more important when raising European Nightcrawlers (E. hortensis). While I still wouldn’t recommend the use of buckets, in my experience (and based on what I’ve read) a deeper tub system or bed seems to work better than shallower tubs/trays and stacking systems.

Now, getting to your main question there. As per usual (with vermicomposting) there is no set-in-stone answer to that unfortunately – well ok, there is ONE answer that never seems to change: “it all depends!
😆
Seriously though, it really does depend on a lot of different factors, and as such, worm densities from one system to the next can vary substantially. I’ve read reports of professionally managed systems reaching densities as high as 4 lb (or more) per sq ft, believe it or not! My guess is that the “optimal” density for a well looked after home system might be more along the lines of 1/2 lb – 1 lb per sq ft.

My question, though, has always revolved around depth – I’ve never seen mention of a standard depth used for these measurements. Obviously, all your worms aren’t just sitting on top of the bed in one big gob. You would need to collect everything from at least the top few inches, and even if there was a standard depth used, we’d also need to remember that Red Worms don’t always do what they are expected to do! I’ve seen lots and lots of worms hanging out down in wet mucky zones of plastic tub systems, for example.

If you are looking for a reasonable estimate for stocking density (i.e. the quantity of worms to add to a given system), I might suggest going with 1/4 lb – 1/2 lb per sq ft. So, if your bin measures 4ftx3ft, you might thinking about stocking it with 3 lb – 6 lb of worms. I tend to be a little on the conservative side though, so don’t take that as “gospel”. In all honesty, I prefer to let a worm population grow into a given system rather than trying to start with an “optimal” density. In my mind, it doesn’t make all that much sense to optimize the worm population when the system itself is not yet optimized (generally takes place over time).

Anyway – not sure if I really answered your question, Al! I’m hopeful we’ll see some input from others as well.
8)

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Comments

  1. The last time I emptied my flow thru, about 60% of the worms were in the top 4 inches, 15% were in the middle section, and 25% were in the bottom 4 inches. It seems that the bottom sections had just as favorable conditions as the top. When I think of my flow thru, I count the bottom, which is like a false bottom, as a suface. So, my flow thru has 2 surfaces and processes rather quickly, my tub bins have 1 surface and moves along at a slower pace, and the Worm Inn has 6 surfaces. I don’t have a Worm Inn but, I have read a lot about them.

    • Rezim
    • September 17, 2010

    You should differentiate whether you use worms for breeding or for composting.

    Manual of On-Farm Vermicomposting and Vermiculture states that:
    “… densities, higher than 5 kg/m^2 (1 lbs/ft^2) begin to slow the reproductive urge, as competition for food and space increase. While it is possible to get worm densities up to as much as 20 kg/m^2 (4 lbs/ft^2) the most common densities for vermicomposting are between 5 and 10 kg/m^2 (1 to 2 lbs/ft^2). Worm growers tend to stock at 5 kg/m^2 and “split the beds” when the density has doubled, assuming that the optimum densities for reproduction have by that point been surpassed. …”

    Remember, compost worm populations can be expected to double every 60 to 90 days (under certain conditions).

    If worms are used for composting, then the more worms you have, the better. The density will stabilize at a certain point anyway.

    Hope that clears it up a bit.

    P.S. Bentley I agree one should let their worm population grow to the optimal density, not start with it. Half the recommended density is fine. You’re gonna have it double pretty soon anyway.

    • Al
    • September 17, 2010

    Wow!! I guess this counts as part of my 15 minutes. Never thought it would be worm related though.

    My goal in seeking the density of worms per square foot was to get a better idea of the amount of “food” my system could process. As you suggested, my intent is to let the “…worm population grow into…[my] system…”.

    Honestly, I have done lots of reading (and I always seem to wind up back at your wonderful site). And in my reading (I believe it was an article from Ohio State) there was mention of 1/2 pound (approximately 500 worms) per CUBIC foot. Just thought I would share that with you.

    Again, thank you for your wonderful site.

    Cheers,
    Al

  2. After I watched this video about Jack Chambers, I noticed his bins are longer than deeper.
    https://www.redwormcomposting.com/announcements/jack-chambers-on-pbs/

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