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What’s a worm compost bin?
While the actual container can be very basic or highly specialized, a worm compost bin is just a contained environment where composting worms live. The worms spend their days slowly consuming organic matter and excreting waste, known as castings. The worm castings are incredibly beneficial when added to garden or potting soil.
So in a nutshell, a worm compost bin is just a place to keep worms so they can turn food scraps and waste paper into soil enriching, moisture retaining castings. In other words, for the initial cost of a few worms and a plastic tote or two, you can reduce your household’s garbage output and gain a powerful soil amendment.
So a worm compost bin is where the composting worms live. Got it.
So what can you use for a worm compost bin?
You can use just about any sturdy container as long as it has a lid. Most worm bins are made from plastic, since it’s durable, lightweight and inexpensive. Look for BPA free plastic. The easiest and cheapest way to get started in vermicomposting is to use a basic plastic tote. If you decide to keep on worm composting, then you can upgrade to a fancy worm tower or tiered bin down the line.
How to set up a worm bin for composting
The plastic tote or container should be at least 10-12″ deep and 12″-18″ wide, with a secure lid*. So long as you meet those rough minimums, you can pick a size that makes sense for where you’ll be storing the farm.
Worms aren’t into bright lights, so if you’ll be keeping your worms in a bright area, use an opaque container. My worms live in the basement, where it’s usually dark, so I used a clear bin. I like being able to see what’s going on without taking the lid off.
The worm bin needs adequate drainage and ventilation. The easiest way to manage this is to drill 1/8″ holes in the bottom and sides of the container and in the lid.
*if your container doesn’t have a lid, you can cover the bin with a screen or leave it open. If it’s open, be sure you place the bin somewhere household pets can’t get to it.
Your worm bin may secrete liquid. Some worm farmers welcome, and even encourage this, calling it ‘liquid gold’. They collect this runoff and use it in their gardens. In fact, some of the more elaborate worm bins are set up with a spigot to make collecting it easier. Others claim that if your bin is properly maintained, there shouldn’t be much excess liquid. So far, I have not found evidence that definitively settles this question. My bin has never produced enough excess liquid for me to bother about collecting it and my worms seem happy and productive, so I don’t worry about it.
Regardless of whether you’re in it for the liquid gold or not, you need drain holes in the bin so that if and when there is excess liquid, it drains out and doesn’t drown your worms. If you see much liquid leaving the bin, you’ll need to put a tray under your bin to avoid a mess.
One of my worm bins – just an plastic tote with small holes drilled around the sides and in the bottom. The lid has holes, too. It sits on a wire shelf to allow some air flow through the bottom holes.
If you don’t want to make your own worm bin, or you’re ready to upgrade, here’s some top notch worm bins
Bedding for a worm composting bin
Your worms need a place to hang out while they turn food scraps into sweet castings. The best bedding for a worm bin is shredded paper. Ideally, the paper will be minimally treated and free from heavy dyes or coatings. Brown paper bags and paper junk mail are excellent bedding sources.
The bedding materials should be torn or shredded into small pieces or strips. Over the years, I’ve found that a combo of crosscut paper and larger torn pieces of brown paper makes great bedding. The bedding must be loose enough that the worms can easily move through it – so small strips or pieces are ideal.
If you can shred it into small enough pieces, cardboard or pulp egg cartons can be great bedding materials, too.
Preparing bedding for a worm bin
Once you’ve broken the paper bedding down, put a few inches of it into the tote. Add a cup or so of garden soil to introduce grit and beneficial bacteria to the bedding. The soil should be slightly damp and free from pesticides or synthetic fertilizers.
Mix the paper bedding and soil together. At this point, you should be able to easily sift the bedding with your hand. The bedding should feel slightly damp – but not so wet that the paper sticks to your hand.
If the bedding feels dry to the touch, very lightly mist the top with water, then mix it all up again. It’s better to have bedding that’s slightly dry than bedding that’s too wet.
Ugh, the paper is sticking to my hand and feels pretty damp
No problem! Just mix in some more paper. Keep adding handfuls of shredded paper until the bedding feels barely moist.
My bedding feels slightly damp but it’s also really clumpy.
You don’t want clumpy bedding. If yours feels a little chunky, add in some smaller pieces. Larger pieces of paper can sometimes soak up too much moisture and end up sticking together. Mixing in some finer pieces will help absorb excess moisture and distribute it.
Ideally, let the bedding sit for a few days before you introduce your worms. Check the moisture level daily and add a bit of water if needed. Once your worms are in the bin and active, you likely won’t need to do much to regulate the moisture. But at the beginning, check it and keep the dampness consistent.
Interior of one of my worm bins, showing the finely shredded paper and larger pieces of paper that make up the bedding. The combo seems to work really well for my worms. The small bits of paper break down more easily and stay loose but the larger pieces of brown paper take longer and help the bin maintain a consistent moisture level.
Note that there are no worms climbing up the sides of my bin – that suggests they’re happy in the environment.
Introducing worms to the worm bin
Once you’ve prepared your worm farm, it’s time to welcome home the wigglers. Most people order their worms online but you can certainly but them locally if they’re available!
What kind of worms go in a compost bin?
You want red wigglers, my friend. Get yourself 500-1000 of them, unless your bin is substantially larger. No, the worm farmer won’t count them out for you – they weigh them to gauge the quantity.
Why red wigglers?
They’re really efficient at turning organic matter into castings. While a worm bin is a very easy way to turn waste food into compost, it’s not a very fast method. So you need worms that are really good at the job.
Where do I buy worms for my worm bin?
Unless there’s a local source, you cannot go wrong with Uncle Jim’s worms. You’ll get top quality red wigglers at a fair price. And you can feel confident your worms will arrive safe and sound.
Arrive safe and sound…you mean they’re going to mail me worms?
Yes indeed. A few days after you place your order, you can expect a box full of worms to arrive. They’ll be shipped in a bag full of bedding and will arrive no worse for the wear, baring extreme temperatures. Don’t order worms if the outdoor temperature is below 40 or over 85.
Open your worms as soon as possible. Follow any instructions included with your worms, since the seller will likely have some suggestions for unpacking and acclimating them.
Putting worms in the worm bin
Take your worms to the bin and gently dump the contents of the bag in. The worms will, understandably, be a little dazed by the abrupt change. Cover them with a few inches of bedding and leave them alone for a few hours.
Check the bin and moisture level of the bedding after your worms have had a little time to acclimate. The worms should be deep in the bedding, not climbing the sides of the bin. The bedding should still feel damp. If it feels dry to the touch, mist it with a little water but don’t mix things up.
Got the worms tucked into their new home?
Awesome! It’s time to feed them.
Feeding compost worms
You can feed your worms a huge range of foods. But there are definitely some things they prefer and some things you shouldn’t give them.
In general, your worms will enjoy all parts of fruits and most vegetables – that includes peels and cores, as well as bruised or mushy areas. They seem to love spent coffee and tea. My worms actively prefer tomatoes and apples – if I put either of those in the bin, they burrow right in and eat them first.
What not to feed your worms
I like to use the picnic rule – if I wouldn’t let it sit out at a picnic in August, it’s probably not a great thing to give my worms.
- Don’t feed your worms meat, fish or fats. The worms won’t necessarily mind these but there’s a good chance they’ll spoil before the worms can finish them. And that will lead to all sorts of issues. No eggs or dairy, either.
- Avoid citrus as it can raise the acidity level in the bin. Worms do not thrive in an acidic environment, so it’s best not to add anything acidic to their bin.
- Alliums can sometimes throw off the balance of the bin and worms will not readily eat them. They can also make your bin stinky.
- No pre-packaged, processed foods or leftovers – while your worms might enjoy a slice of pizza or some leftover mac and cheese, it’s not great to introduce sodium and preservatives to the bin. And, like meat or dairy, there’s a significant risk that it will spoil before the worms process it.
- No sweets or chocolate and no breads.
You really can’t go wrong if you stick with minimally processed grains (oatmeal, cooked rice or lentils), fruits and vegetables.
How to feed compost worms
Sweep away a small section of bedding to expose the upper layer of the castings. You’ll likely see some of your worms when you do this. Put all of the food in this spot, in a single layer. Recover with the bedding.
You will need to add more bedding materials from time to time. The worms break down the bedding, too, as does the natural process of decomposition. It’s easiest to just throw a few more inches of fresh bedding on top after you feed the worms.
It’s important to bury the food under bedding. This helps keep the worms comfortable while they work on the food and minimizes food odors. Burying the food also reduces the potential for attracting insects.
How to maintain a worm bin
Honestly, composting worms are just about the easiest livestock out there. The biggest chore is keeping the bin properly moist, especially at the beginning.
In the early weeks of your worm farm, you may find the bedding dries more quickly. Check it daily early on and lightly mist the top layer with water if it feels dry.
But what if it seems too damp?
Add more dry bedding if the contents of the bin feel heavy or wet. Just sprinkle a couple of inches over the top and leave it alone. It will slowly draw water out of the lower bedding. If the bin feels very wet, leave the lid off for a day or two, as well.
Within a few weeks, the bin will likely reach a state of equilibrium where the moisture level is relatively even. That’s because the food scraps will slowly add moisture to the bedding, as will the worm castings. I haven’t added water to my worm bins in over a year and the bedding has stayed just right. Remember, you’re effectively creating a micro ecosystem in your bin. The more you let the natural cycle of consumption and decay regulate the bin, the better.
How often should I feed compost worms?
There’s really not a definitive answer to this. Wait until most or all of the food is gone before adding more. Some foods will take the worms longer to work through than others. And while the worms are consuming the food scraps, the natural process of decay is also breaking down the food. So a food that’s more prone to rotting, like a banana, will be gone long before a carrot. The size of the food matters, too. Smaller bits of food will break down faster than a whole tomato.
Also, worms are less active in very hot or very cold temps. So your worms may slow their consumption in winter if they’re in a colder basement, for example.
The best course is to keep your worm scraps in a bag in the freezer and only add them to the bin when the worms have mostly cleaned their plate. This also has the benefit of preventing pest like fruit flies from setting up shop in your worm bin.
If you’re building up food scraps faster than you’d like, consider chopping them up before you feed them to the worms. The smaller size will speed things up.
You can, of course, always add another worm bin if your household is generating a lot of food scraps and waste.
In this photo, you can see that my paper bedding was clumpy. The pieces were too large and once they picked up water, they stuck together. The larger chunks held onto water longer, which kept the entire bin too wet. As a result, my worms were constantly crawling up the sides of the bin to get out of the heavy, wet paper.
How to collect worm castings
There’s one final piece of the puzzle – how do you actually get to the worm castings?
If your bin is functioning well, the castings will be a dense layer under the bedding. The worms may be in the castings but they’ll mostly be in the uppermost layer and in the layer of bedding.
Worms will go where the food is. Knowing this, you can manipulate your worms to move, leaving clear access to that layer of castings. Here’s a few ways to harvest worm castings.
The partition method
This is just about the easiest way to get castings since you don’t have to empty the bin or relocate the worms.
Start placing the food scraps on the far edge of the bin. The worms will congregate in that half of the bin. Gently scoot the bedding over, the scoop out the castings. If there are some straggler worms, just pick them out and drop them in the other side. When you’re done harvesting, spread the bedding back over the side, and add more if needed.
The ‘new bin’ method
This method basically coaxes your worms to pick up and move. You’ll need a second bin ready to go, including bedding.
The easiest way to move your worms to a new bin is to use a bin that can stack inside your original bin. Set it up just like your first bin, but drill a few larger holes (1/4″ to 1/2″) in the bottom.
Place the new bin inside the old bin, on top of the bedding. Begin feeding your worms exclusively in the upper,new bin. The worms will migrate through the holes, into the new bin. That means they’ll leave behind the castings, ready for you to collect.
When it’s time to collect the second round of castings, put your original bin on top of the ‘new bin’ and repeat the process. Just make sure both bins have holes in the bottom large enough to allow the worms to migrate.
Some people actually do this with a three bin set up. The bottom bin is always the bottom bin and it’s there to collect any liquid runoff or worms that decide to sneak out the bottom holes. The bottom most bin doesn’t really need to be a full on set up in this scenario. It just needs to be large enough that the upper bins can sit in it and deep enough to collect and corral stray worms. If you find any escaped worms, just drop them back in.
The dump and transfer method
This is the messiest but fastest way to collect worm castings. Put a large piece of cardboard or a plastic sheet on the ground. Gently turn the contents of the worm bin out onto the cardboard. Spread the castings out slowly. The worms will flee from the light and move into the deeper pile of bedding -keep moving the pile along until the worms have congregated in one area. Then collect them and their bedding and put them back in the bin. They’ll need fresh bedding and you may need to add moisture until the bin regulates itself.
I’m not a fan of this method. It’s very disruptive to the worms and their ecosystem. But if you need to get a lot of castings in a hurry, it will work.
The scoop method
When you just need small amounts of castings, you can simply scoop some up and pick the worms out, putting them back in the bin.
Freshly harvested worm castings
Worm concerns – how to keep your compost worms contained, happy and healthy
If I drill holes in my worm bin, how do I keep the worms from escaping the compost bin?
Great question! Worms are very small and very squirmy and if they don’t like the environment they’re in, they’ll wiggle on out. To ensure your worms stay put, you can glue window screen over the holes you drill. If you do this, cut small pieces of screen and glue them to the outside of the bin. Air and moisture will be able to pass, the worms will not.
Obviously you can’t glue screens over the holes you drill for your worms to migrate, since that will defeat the purpose.
But….you can also keep your worms in check by making sure the worm bin is comfortable for them. That means it’s neither too wet nor too dry. And that the bedding material isn’t too acidic or too densely packed – and that you don’t overfeed your worms. If that all sounds like a lot to manage, don’t worry – it’s much easier than it sounds to keep your worms happy.
How to tell if compost worms are happy
Unfortunately, worms don’t give us a lot to work with when it comes to gauging their emotional well-being. But a surefire way to gauge how your wigglers feel about their home is their behavior. If your worms are tucked down in their bedding, concentrated around (and consuming) their food, that’s a good sign.
Do you see worms climbing up the sides of your bin, out of the bedding? Or worms trying to squeeze out of the bin? Then something isn’t right in their environment.
If you’ve got worms clinging to the upper walls of your worm farm, that’s a sign that the bedding is probably too wet or too acidic, or that there are some irritating additives (like dye). It could also indicate that the bin is in an area that’s too hot or too noisy.
In general, worms will not leave their bedding if they are too cold, too dry or underfed. In those conditions, they’ll dig in deeper and even go semi-dormant.
How to fix a bin that’s too wet
More bedding! Simply cover the current bedding with a few inches of finely shredded dry bedding. Don’t add any food to the bin for a few days. The new bedding will slowly absorb the excess moisture. Keep adding new bedding until the moisture level balances out. Remember, you should be able to move your hand easily through the bedding.
What about acidity?
It’s a little harder to gauge this. But if you’ve addressed the moisture level of the bedding and your worms are still trying to escape, it’s likely something in their environment is too acidic or some additive in the bedding is causing discomfort.
First, remove any acidic foods from the bin if present – things like citrus or alliums.
Then move half of the existing bedding to one side and replace with finely shredded, undyed paper or other cellulose. Use the least processed, most ‘natural’ paper you can find. Add a small amount of food to this side and cover with more of the new bedding.
If your worms have been reacting to high acid levels (or harsh chemicals or dyes in the bedding), they should readily move to the ‘gentle’ bedding.
Remove and replace the rest of the bedding if your worms flock to the new bedding.
One other way to tell if your worms are doing all right…
They’ll make more worms! If you notice some new additions to your bin after a few months, that’s a good sign the conditions in the bin are right. Worms will keep repopulating until they reach the maximum level the bin can support. By contrast, if your worm population seems to be dwindling, something isn’t right in their world.
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I’ve lifted away the upper layer of shredded paper bedding and you can see worms congregating at the surface of the castings. Happy worms will be under the surface of their bedding and in the upper layers of the castings. If you see worms on the sides of your bin, something is likely wrong with the bin.
Don’t overfeed them
It’s tempting to just keep adding food scraps. After all, we’re doing this for those sweet castings – and surely more food means more, er, output, right?
Sadly, no. If you just keep adding food to the bin, it will simply rot. While that’s not the end of the world in small amounts, too much rotting food can throw off the delicate balance of the bin and be harmful to the worms. It’s best to wait until all or most of the previous feeding is gone before adding more.
Try to avoid disturbing them
Ok, I’m not going to lie – it’s really hard not to poke around in the worm bin to see how things are going. Especially at first. But every time you disturb the bedding or the bin, you disrupt the worms entire world. That can stress the worms out and slow down the entire process. I’m not saying you shouldn’t check on your worms – you absolutely need to take a peek down in the bedding from time to time to see how things are going. But try to limit those welfare checks.
Stop feeding them (temporarily) if you get an infestation
It’s happened to most of us. Our bin, despite our best intentions, ends up hosting a fruit fly party. If that happens, remove all the big pieces of food from your bin and don’t add anything else for a few days. When you do resume feeding, freeze every scrap first. Add only small amounts of food, no more than the worms can work through in a few days. Without rotting food as a host, most pests will die or move on. You can move the bin outdoors during this time if you need to, as long as the temperatures are between 45 and 80 degrees.
This was my biggest challenge the first year. Fruit flies got in and took over and it was a miserable development. I’m unbelievably grateful to Bella from Pentagram Potager for telling me to freeze my scraps and add more bedding. She saved my worm bin and my sanity!
Cure the stink
Your worm bin shouldn’t smell musty, rotten or gamey. It really shouldn’t have a strong odor at all. If that’s not the case, you’re likely overfeeding (or giving them foods they simply won’t consume) or your worms or your bedding is too wet. Adjust your feeding schedule or add more dry bedding, accordingly. Your worm bin should smell earthy, not like a garbage can.
Indoor composting with worms
It might have sounded weird at first, but hopefully now you see how easy it is to give vermicomposting a try. Your worm bin can be a simple, unobtrusive way to turn food scraps into a premium soil amendment. Even if you have an outdoor compost bin, consider adding indoor composting with worms as a way to process more tables scraps and extra food.
Got questions? Post them in the comments! Have strong feelings about setting up a worm composting bin? I want to hear from you! If you’ve tried your hand at worm composting, what do you think?
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