I freshened up our big worm bin today and I thought I’d report on what I did because I get a lot of questions about worm bin maintenance.
First, I want to say this is just how I go about it. Other people will have different methods and habits. Worms are forgiving and reasonably adaptable, so you have a whole lot of leeway in keeping a bin. As long as you don’t let the worms dehydrate, drown, bake, or utterly starve, you’re going to be okay.
Our worm bin is pretty big (5 feet long), and made of pine boards. It bears an unfortunate resemblance to a coffin, but it works wonderfully. I used plastic storage totes for my worm bins before we built this, and while those worked fine, I really like my big bin for two main reasons. The first is the size. It can take whatever I throw at it. It takes all my kitchen scraps, except for the really choice stuff that goes to the chickens. The second selling point is that the wood breathes, and that seems to make the worms happy.
Maintaining the Bin
The Conceptual Divide
I divide my bin into two areas, left and right. There’s no physical barrier between the sides, just a conceptual distinction. Usually one side is working and the other side is resting. This division is easy to make in a long, skinny bin like mine, but can be managed in a smaller bin as well.
Basically, once you’ve got a worm bin going, there will come a time when you’ll need to harvest some of the castings. Those castings are valuable in the garden, and the worms don’t want to live in their own waste. You’ll know its getting close to harvest time when you see pockets of scraps here and there, but mostly the texture of the contents looks like soil or coffee grounds. Or maybe fudge, if it’s more wet and compact. Fudge is a less than ideal environment for worms.
In the picture at the top you’ll see my most recent working side. There’s a lot going on in there still, some big food pockets, wood shavings everywhere, but the texture is becoming too black and dense overall. Compost worms like a little air, a little “wiggle room” and a diversity of habitat. It was past time to change this working side to a resting side.
Resting comes before harvest. This is where dividing the bin in two comes into play. Resting means no more feeding, so that the worms will finish up whatever bits of food are left around. But of course you can’t starve out your worms, so you only rest half of the bin at a time. To do this, you put your food scraps on one side only. The worms on the resting side will finish up whatever food pockets remain and then migrate over to the active side for the fresh grub.
This doesn’t happen quickly. I’ve never made note of how long migration takes–it will vary, depending on many factors. I just poke around in the resting side whenever I happen to think about it. If I don’t see anything recognizable beyond non-digestibles, like avocado pits, fruit stones and egg shell shards, and I know it’s ready for harvest.
There will also be a few worms left, no matter how long you wait. More on them later. If your bin is outdoors, other insects like sow bugs might be in there too, but are harmless.
This is the process in a nutshell:
When your bin is looking mostly done, ie full of castings, rest one side of it. This means you feed only on the opposite side. When all the recognizable scraps are gone from the resting side, you harvest the castings. Then you can put fresh bedding in the empty space, and start encouraging the worms to move to that side. Soon, you will be able to rest the opposite side of the bin, and eventually harvest it. And so it goes, back and forth.