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.
Below is the resting side of the bin. I put a layer straw on top for a little insulation.
Again, nothing goes into the resting side while it’s resting, unless it needs water to keep it from drying out.
Below is how it looks with the hay scraped off. See? Nice and dark
And here it is close up.
The pale things are mostly eggshells, along with a few wood shavings that drifted over from the working side. There’s a soldier fly carapace on the far left, dead center. I ignore those.
Eggshells never really break down in a worm bin, but I don’t mind them ending up in the garden along with the castings. If I wanted pretty worm castings–say if I were selling them–I wouldn’t put eggshells or fruit pits or pumpkin seeds into my bin at all. These things just linger and are hard to sift out.
Harvesting the Castings
Harvesting castings is the only hard part about keeping a bin–and it’s not even hard, it’s just somewhat less than convenient. No matter how long you rest one side of the bin, there will always be a few confused worms living in the finished castings. If you bag them up with the castings, they’ll die.
So you have to sort out your feelings and responsibilities vis-a-vis the worms. I won’t blame anyone for letting the strays perish (they had warning, after all) but I have guilt, so I do my best to sort them out.
However, hypocrite that I am, as I do so, I entertain myself by trying to envision some system where I could enlist the chickens to do the job for me. They’d be great at it, of course, and the worms would give them a good protein hit, but they’d toss the castings everywhere in the process, and add their own fertilizer to the mix. Yet, some sort of containment system might work…
Daydreaming aside, until I invent that Chicken Powered Terror Dome for Worms, I have to sort the worms myself. There are various tricks for this. None are foolproof. I believe I’ve blogged about them before.
After trial and error I’ve come to the conclusion that it’s just as easy to pick them out by hand as to do anything else. The pyramid system and the like work, but are not any faster. Worm sorting would be most fun with someone else–sort of like shelling peas–but today I listened to an audiobook while I worked, and that was good. too.
Harvest is simply reaching into the finished side, gathering up a handful of castings, and dropping them into a five gallon bucket. At every handful I pull out any worms I see and toss them into the working side of the bin. Sometimes I find a bit of paper, like a coffee filter that is not quite finished. That also goes back into the working side. (Note: If I were to start to find food scraps, though, I’d stop and let the bin rest some more.)
Any fruit stones or avocado pits or sticks, things that will never break down go into a smaller bucket for later disposal in some remote corner of the yard. The process actually goes pretty fast. I harvested 5 gallons of castings in less than an hour. You could go through a plastic tote-type bin much faster.
Making a New Working Side
After harvest you’ll have empty space–and that space will become the new working side, which means you need fresh bedding for the worms. I usually start by robbing some of that from the other side of the bin. Anything that’s big enough to notice, like a corn husk or a coffee filter or a handful of straw, I’ll grab. Today, I scraped the top layer of my working side into the empty part of the bin.
Worms like materials that provide some fluff or air to the texture of the bin. I like to use a combination of materials, whatever I have on hand. Shredded newspaper is a standard bedding material, but we don’t take a paper. Today I used rotted straw, wet pieces of cardboard, lots of dead leaves, a few wood shavings and a little bit of garden dirt for grit.
Note regarding paper: I wouldn’t use anything bleached or anything printed with shiny inks. Plain corrugated cardboard is great, as is brown paper.
I also mixed in some well composted cat litter into the mix, but that’s eccentric, and possibly dangerous, and another story for another day.
As you collect your materials, wet them down. They should be moist, not soggy. I dip everything I use in a bucket of water before introducing it to a bin. Worms don’t want to wiggle through dry, scratchy stuff, but they’ll also drown in puddles.
Above you can see the left side of the bin, the new working side, full of fluffy, moist, leafy material. On the right is the new resting side.
The worms are going to be much happier with all the breathing room in the new space. I’ll start adding food on left side–a bit more conservatively than usual, since there isn’t a big worm population over there yet. The worms living on the right side will start moving over pretty soon, leaving the pure castings for the next harvest.