Vermicomposting: Easy and Efficient Composting with Worms

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By Dave Whitinger

2011-08-16/dave/0572aeBanana peels, apple cores, coffee grounds, spent tea leaves, corn silks and husks, leftover bits of peppers and tomatoes, and countless other treasures like these are produced as refuse in most of our kitchens. If we're not composting them, then we're cheating ourselves out of one of the best tools for improving the soil for our plants! We should be composting them, and the best way that I've found to compost kitchen scraps is vermicomposting.

Vermicomposting is the process of maintaining a bin of worms who you feed with your various kitchen scraps. The basic idea is to create a bin with drainage and airflow provided by means of holes drilled in the bottom and lid, and fill this bin with moist bedding. You then periodically feed your worms by burying organic matter in the bedding, which the worms quickly find and eat.

This eaten and digested material is excreted as "worm castings", a valuable fertilizer that can be used to dramatically improve your soil and potting mixes. Compared to the soil that earthworms live in, their castings contain five times more nitrogen, seven times more phosphorus, and 11 times more potassium. On top of that, the castings are mild and can be applied directly to plants without burning them. Moreover, the nutrients from castings are water soluble, so you can create a powerful foliar spray with "earthworm tea".

This article introduces you to the concept of vermicomposting, and gives a tutorial on building a basic bin. It's the author's hope that you will experiment and later expand by building larger and more complex bins.

2011-08-16/dave/084641Gather your materials

Firstly, you're going to need a bin. An excellent starter bin is the Rubbermaid 10 gallon "Roughneck" tote that is sold in most "big box stores". It's shallow depth is perfect for vermicomposting, because if you use something too deep your castings will get compacted and crushed under their own weight.

Secondly, for the bedding, you will also need cardboard: lots and lots of it. If you have ready access to coconut coir, that will work perfectly fine as a cardboard alternative.

Those are the only two absolute requirements, but let's move a little beyond that and add some extra things that earthworms generally love.

Go out and collect leaf litter, crushed twigs and small bits from the forest floor, then on your way back pick up some old decaying mulch from the flower bed, find a bit of wood ashes or ground limestone (to help with the pH). Drop by the pasture for an old and dry cow plop or two. Get some sand, some soil from your garden, sawdust from the workshop (avoid cedar and other aromatic woods, though), old and spent potting soil, etc. We're trying to make a bedding material that is rich in variety. Think of the forest floor; that's what we're trying to replicate.

2011-08-16/dave/8c6ec1Making the bin

Take your tote and drill some holes in the bottom for drainage, and then drill holes in the lid. The holes in the lid should be small enough to let air flow through, but not so big that they let in a lot of light.

Shredding the cardboard

When I first got into vermicomposting, I would sit on the floor with the family and we would spend time ripping cardboard. We would first carefully remove all the tape, then we ripped the cardboard into shreds. This job quickly became tiresome, so we experimented with using boxcutters to cut them into long strips. That job was a tiring and dangerous one! You work hard, the fingers cramp and the back aches. Before long, I found myself alone and the family had gone on to other activities. Several hours later my collection of cardboard was finally cut into small pieces.

Well, I have since discovered a better way. Take a large trash can and cram it full of all your cardboard. Then fill it to the brim with water and leave it to soak for several days. At the end of this soaking time, you pull the cardboard out piece by piece and simply shred it directly into a waiting container. The tape peels right off and is placed into a separate trash bin. It couldn't be simpler, easier or faster! A job that used to take hours now takes just a few easy minutes.


Putting the bedding together

Start creating your bedding by laying down your material in layers.

Some cardboard: Some mulch, twigs, leaf litter, etc.




More cardboard. More leaves, twigs, soil, etc.




Yet more cardboard You're getting the idea



Now set the bin in a safe place where it won't get too hot or cold, and where any drippings from below can be caught. In my case, I sometimes stack them on older bins that are being finished up. Make sure the bedding is nice and moist, then place the lid.



Obtaining the worms

You could go out and dig some worms out of your garden, but these are not the most efficient species of worms for indoor vermicomposting. For our purposes, we want Eisenia foetida, also known as "Red Wigglers". You can order them online from many sources. One pound of worms will be the perfect amount to get your bin started.

When the worms arrive, empty them out of their sack directly onto the bedding and leave them alone. They will burrow down into the bedding within a few hours. At this point, leave them completely alone for a week, so they can get established and begin building up the beneficial bacteria that they will need for processing food wastes.

Don't worry about them starving: the cardboard and bedding will be food for them!

Feeding your worms

Once this introduction time has elapsed, go ahead and start putting some scraps of food in the bin. Peel back the cardboard layers with a tool like a 3-tong hand rake, drop your scraps in, and then make sure you completely cover the scraps with the bedding. The worms will soon find these scraps and start eating them.

Add scraps very sparingly during the first couple months of your bin's life. Until the earthworm population has grown, it is very easy to accidentally introduce too much food into the system and overwhelm everything. If that happens, just stop adding altogether until all the food waste is gone.

Every few weeks you should sprinkle a couple spoonfuls of wood ash or ground limestone on the surface. The action of earthworm digestion has an acidifying effect, and this action will counter that.

What to feed them?

Most things that are produced in your kitchen can be fed to worms. Fruit and vegetable matter, coffee grounds, and tea leaves are excellent. Avoid strong smelling root crops like onions and garlic. Avoid entirely dairy, meat and grain products.

Harvesting your worm castings

It won't take long for the bin to start dripping black liquid out the bottom. Capture this liquid and use it, diluted, to water your plants. As time goes on, your bedding will start to disappear and the bin will be filled with castings. These castings look like black soil and have a lovely earthy smell.


It is at this point that I begin contemplating the creation of an entirely new bin, moving the worms to the new bin and completely harvesting all the castings. Because the worms avoid the light, you can simply scrape the top layer of castings away, and within a few minutes the worms will have retreated further down. Repeat this process until you have harvested most of the castings, and then dump what's left into your new bin.

Managing your increased populations

The worms reproduce readily, and it won't be long before you have thousands and thousands of worms. You will at some point want to split your population in two and have two bins going simultaneously. You can also experiment with larger outdoor bins.

2011-08-16/dave/1ecf54Pictured to the right is my outdoor bin, made from an old four foot wide galvanized watering tank. The bottom had rusted enough that it wouldn't hold water anymore, so I punched several holes for drainage and filled it with bedding. It is now sitting at the edge of the woods where, except for first thing in the morning, it is in the shade all day.

I built this bin with bedding the same way I did my indoor bins, and introduced a handful of worms from an existing bin. It is now full of worms and doing very well! I add scraps from the garden and the kitchen to this bin every couple weeks. Due to our ongoing drought, I have had to water it a few times a week in order to keep the moisture levels up.

Using the worm castings

There are claims out on the web that worm castings will double the growth of your plants. Indisputably, worm castings are an excellent soil fertilizer and conditioner, and will give you excellent results wherever you use it. I spread it as a thin layer on top of the soil of my container plants, and I also spread it around my gardens.

Later this year, my plan is to conduct some growing experiments where I grow the same variety of seedlings in several different soil types, and I will be using worm castings in that experiment. I expect to see some dramatic results.

I hope this article encourages you to give vermicomposting a try!

About Dave Whitinger
Thumb of 2020-03-17/dave/72728eDave is the Executive Director of National Gardening Association.
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