Vermiculture composting (vermicomposting, worm composting) is the act of creating rich, organic humus for your garden or lawn by allowing earthworms to help in the decomposition process. Earthworms eat food scraps and poop fertilizer (worm castings). The resulting castings enrich soil by improving texture, increasing nitrogen, trace minerals, and natural growth hormones from the worms themselves.
In this article I will discuss how to get the most out of small scale, indoor vermicomposting without expensive or complicated equipment. You probably already have most of the tools you'll need to get started.
Suggested Materials and Tools for Vermicomposting
- 1/4″ drill bit
- Drill mounted paint mixer (optional, for large scale vermicomposting)
- 18 gallon or larger rubber tub (for larger scale vermicomposting)
- One or more 3.5, 5, or 6 gallon buckets with lids, or a few 10 gallon rubber tubs with lids
- Instructions to make castings harvester + tools and materials (1/8 inch screen) http://whatcom.wsu.edu/ag/compost/pdfs/LowCostWormCastingHarvester.pdf
- Litmus paper or pH reader
- Soil moisture meter (optional)
- Water proof thermometer
- Bedding material
- Food (mostly waste food from your kitchen)
- Agricultural lime (possibly)
- Small fan
Earthworm Species for Vermicomposting
- Red Wiggler – Eisenia fetida
- African Night Crawler – Eudrilus eugeniae
The most popular species for composting are Eisenia fetida, or simply the “red worm” or “red wiggler” although their coloring is considered brown with buff bands. They are often mistaken for and even found with Eisenia andrei whose coloring is more red, but is of about the same size. Both worms perform best at 77°F and will tolerate temperatures from 32-95°F, with moisture levels at about 80-85%. Red worms are the most commonly used species for vermiculture.
Eudrilus eugeniae (African Night crawler) is my personal favorite for indoor vermicomposting. It is the fastest compost turner and reproducer of all three species. For optimum performance it needs to stay between 60-86°F, moisture 80%. It can tolerate temperatures down to 40°F or so.
No matter which worm you choose, you'll want one pound of worms for each square foot of compost/bedding. A 3.5 gallon bucket is about 1 square foot.
What You Need for an Earthworm Compost Bin
“Flow through” bins are popular and there are a multitude of commercial bins and do-it-yourself instructions available. Personally I prefer simpler bins, for a couple of reasons.
Flow through bins create conditions where it is easier for anaerobic bacteria to get a foot-hold and proliferate. If anaerobic bacteria take over the bin it will stink and your worms will be sickly if not dead. At this point your bin will have to be cleaned thoroughly, and it can be a real pain, depending on the size and extravagance of the bin.
The secret to happy and healthy worms is simple:
- Fresh bedding
- Correct amount of food
- Frequent casting harvests
- Thorough, frequent bin cleaning
Although worms do not seem to mind living in close proximity with one another, eventually when kept in the same dirty bin for too long, their castings and other waste materials start to add up. That's not healthy–no one wants to live in their own waste material. That's why I advocate frequent casting harvests and bin cleanings.
The Earthworm Bins I Use
I recommend 3.5 (pictured below), 5 or 6 gallon plastic buckets or at largest, 10 gallon rubber totes. Several small bins are preferable to one large bin because of maneuverability. A 3.5 gallon bucket filled with compost and one pound of worms will weigh between 15 and 20 pounds.
Note the rows of holes below the bin's rim. Ventilation is very important to your worms so only fill the bin to the bottom row of ventilation holes. I like to use lids on my bins to prevent escapees, making the ventilation holes even more important.
Bedding for Your Earthworm Bins
If you can get it, my favorite worm bedding is “fine screened leaf compost”. It can be found at your local wood and leaf recycling center. Towards spring they usually run out, so in the autumn, I take our truck down and get couple yards, then shovel it onto a tarp outside and cover with more tarps. It's important to cover your leaf compost if you live in a climate with a lot of precipitation, or it will get too wet and rot.
If you make your own leaf/lawn compost, it should work great as long as the compost is past the thermophilic stage when you use it for your worms. (You don't want your worms to get too hot.)
To make leaf compost go further, mix it about 1:2 or even 1:1 with coconut coir. Coconut coir is sometimes processed in salt water so look for garden grade coir. Coir is a great carbon source, absorbs and retains moisture really well, and helps fluff your compost, making the bins lighter and easier to handle.
Other Worm Bin Bedding Options
- Shredded news/office paper (black ink only, no glossy paper) – very commonly recommended
- Paper towels
- Fast food cups
- Paper plates
- Coffee/coffee filters
- Used loose tea/teabags
Make sure these are all chopped or shredded really well as some of them take longer to decompose than leaf litter.
What I Don't Use For Worm Bin Bedding
- has to be aged properly to be safe for your worms–fresh manure is too “hot” and will kill the worms
- might contain de-worming medications which will kill your worms
- has an odor, even after aging, and I don't want that in my basement
- often contains E-coli and other bacteria which disqualify the worm castings for organic certification
- creates worm castings that may retain odor of the manure
- Peat Moss is
- Too acidic
- Too expensive
- Slow to regenerate
Four Things Your Composting Earthworms Need to be Healthy
Healthy composting earthworms need the right balance of four main parameters: Moisture, Temperature, Food and pH.
Hydrate both your leaf compost and coconut coir to a moisture level of about 80-85%. To check moisture levels in your earthworm bin, use:
- The squeeze test – Squeeze a handful of the compost as hard as you can, it should just begin to want to drip, but not quite.
- A soil moisture meter, widely available online or at nurseries.
- Bring the compost you intend to use for bedding inside the night before to warm up if temperatures are cool.
- Use a thermometer to monitor temperature in the bins until you get a feel for what external temperature is ideal for your particular set up. For our set up, the room temperature is kept at about 65ᵒ in the winter and 72ᵒ in the summer.
Feeding Your Composting Worms
Worms have no teeth, so they need food mushy and in small bites. Chop the food very small, or even puree it in a blender. Freezing and thawing also helps to soften the food.
For a Single Worm Bin with Red Worms and Bedding
Red wiggler worms eat roughly 1/4 to 1/2 their weight in food scraps each day. For a single bin, bury food scraps or slurry just below the surface of the worm bedding once or twice a week. So for 1 pound of worms, you would need roughly 1.25 to 3.5 pounds of food scraps per week.
For Setting Up Several Worms Bins at Once with Leaf Compost
To mix worm chow in volume, for each 3 to 4 gallons of compost add about 1-1.5 cups of chopped or blended vegetable/fruit matter, and a couple tablespoons of ground grains. Mix compost and food together really well in your 18 gallon rubber tub. Using a drill and paint mixer for this will speed up the mixing process. Divide this leaf compost/worm chow slurry mix between your worm bins.
Recommended Foods for Worm Composting
- Fruit waste; peels, cores leftovers
- Vegetable waste; peels, cores, leftovers
- Limited grains are not only okay, but good for them for the protein content
Foods Not Recommended for Worm Composting
- Too many grains
- Pet feces
- Fresh manure
- Dead bodies
The late Mary Appelhof wrote in her book Worms Eat My Garbage about burying small amounts of leftover meat on the bone with no ill effects.
The pH in your worm bin needs to be between 5.6 and 7.0, the closer to 7.0 the better.
To raise the pH:
- Add 1 tablespoon of agricultural lime per 3-4 gallons of food/compost
- Mix well (If you can still see the lime after mixing, add some water)
- Let sit for 15 minutes
- Take the pH again
- Continue adding lime at that rate until the desired pH is reached
In the unlikely event that you need to lower your pH use:
- Peat moss
- Coffee grounds
- Whole wheat flour
If those don't work, mince or puree citrus fruit and add about a tablespoon per 5 gallons compost, incorporate really well into the compost, and add a bit of water. Check the pH and continue adjusting accordingly.
Vermicomposting – Filling Your Worm Beds
For a Single Worm Bin with Red Wigglers
- Shred newspaper or other bedding material.
- Wet down bedding until it passes the squeeze test (see above).
- Fill worm bed at least half full with damp bedding.
- Add a handful of dirt or compost for grit for the worm's gizzards.
- Add your red wigglers.
- Cover and place in a well lighted room for two days. The light encourages the worms to stay in the bin and explore safely.
- Feed the worms by pulling back some bedding and adding some food scraps. Cover the scraps with bedding.
- Feed again in a few days, when the first food scraps are almost gone.
- Feed once or twice a week, being careful not to overfeed.
- Harvest worm castings in about six months.
For Several Worm Bins with Leaf Compost and Worm Chow Mix
- Fill bins with compost/worm chow slurry mix to ventilation holes – do not to tamp it down.
- Add 1 pound of worms for each 3.5 gallons compost.
- Put the water proof thermometer in one of the bins.
- Put the lids on the bins.
- Set fan on low and aim it for best circulation.
- After 24 hours, check the worms.
You will always have a few escapees, but if most or all of them are trying to escape, you know you have a problem. Double check:
- Inside bucket temperature
- Moisture levels
Adjust parameters accordingly. Note: If inside bucket temp is too high, often your pH is too low.
Harvesting the Earthworm Compost
If using newspaper or other bedding and regular addition of scraps, your compost will be ready in about six months. With the leaf compost/worm chow slurry combination, in 1.5-2 weeks, the worms will be out of food and your bin should be about 1/4 – 1/3 full of castings. (The leaf compost that is left can also go straight into the garden.)
There are a couple of ways to go about harvesting, depending on how pure you want your castings.
Collecting Worm Castings – Method 1:
- Dump entire contents of bin onto a well lit surface.
- While waiting for the worms to move to the bottom of the pile, hose down and scrub bins with a cleaning brush, taking special care to clean the vent holes.
- Separate castings/compost from worms by hand–add product to your finished compost stash or your garden.
- Re-bed your worms into their clean bins.
Collecting Worm Castings – Method 2:
Use 1/8″ screen (hardware cloth) to harvest a purer product. I really like the instructions for the harvester referenced above, but if you find something you like better, by all means try it and let us know how it goes. Remember to clean bins before re-bedding worms.
If you need a small amount of worm compost before the whole worm bin is ready to harvest, you can gently push the bedding aside and reach down into the bottom of the container to scoop up a handful or two. (Worm compost makes great food for houseplants and is a gentle plant food for seedlings, too.)
Whichever method you choose, after a few harvests, you will need to weigh your worms. More than likely you will have gained some worms, but if there are less than what you put in to begin with, you'll need to do some trouble shooting.
How to Start a Worm Bin – Your Guide to Getting Started with Worm Composting
For more detailed information on worm composting, including a comparison of commercial worm bins, worm bin troubleshooting, other critters that may show up in your worm and more, check out “How to Start a Worm Bin – Your Guide to Getting Started with Worm Composting” by Henry Owen. Henry is the Executive Director of the Nature Discovery Center in Bellaire, Texas and loves connecting kids with nature.
Some of the things I like best about “How to Start a Worm Bin“:
- Easy to follow Q&A format
- Basic worm anatomy and reproduction information (great for kids as well as adults)
- Tips for Sizing your Worm Farm
- Ideas for Upcycling a Variety of Containers into Worm Bins
- Troubleshooting Reference Chart and Worm Composting Q&A
- Instructions for making worm compost tea and using worm compost in seed starter mix
The book is free with Kindle Unlimited, and the print version is under $10. It's a great little guide for the beginning worm wrangler.
This is a guest post by Corinna Fritz. Corinna and her husband Dustin share a passion for family, homeschooling, homesteading/self-reliance, nature and small businesses. Corinna's understanding, love and respect for livestock, gardening, worms, and natural flora and fauna began when she was a young girl living on a ranch in Wyoming. These days the Fritz family are small business owners and novice homesteaders on 6 acres of land in the temperate rain forest of Washington state. You can read more about their adventures at: http://cyberscryber.blogspot.com/.
More Common Sense Gardening Posts
- How to Start a Garden – 10 Steps to Gardening for Beginners
- Companion Planting in the Garden
- Small Garden, Big Yield – 10 Tips for a Great Harvest
Originally post in 2013, updated in 2017.