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.
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.