Worm Composting How-to Guide
Compost your scraps with vermicomposting
What is worm composting?
If you’ve always wanted to compost, but you’ve felt confined by the size of your home or the lack of a backyard, then worm composting could be an excellent solution for you! Also known as vermicomposting, worm composting is the creative collaboration between red worms and humans to create compost out of food waste.
But how do worms magically turn food into compost? It’s pretty simple, actually. With the help of some beneficial bacteria, damp paper bedding, and a sturdy bin, you can depend on your worms to eat your kitchen scraps, turning them into rich, useful compost that is perfect for fertilizing your garden and indoor plants (in liquid or solid form).Worms will eat anything that used to be living (fruit and veggies, egg shells, leaves, and grass) and in so doing will produce worm castings (known also as worm humus, vermicast, worm compost, or worm manure), which is nutrient-dense and full of microorganisms.
Why compost with worms?
Make no mistake, worm castings are essentially worm poop! But don’t worry, worm castings are odorless and when properly cared for, your worm compost bin will be a near-effortless way to recycle organic waste in your very own home. They are also highly beneficial for plants. According to the University of Massachusetts Darthmouth, using vermicompost on plants increases germination rates, plant growth, appearance, and fruiting when applied even at a ratio of 10% compost to 90% soil.
Composting with worms has many advantages, but here are the biggies:
- Vermicomposting can be done indoors, year-round.
- Producing compost with worms is generally faster than using conventional compost bins and piles, although it is more labor-intense.
- Worm humus contains very high quantities of water-soluble nutrients and minerals that are ground up and mixed evenly by the worms, making them readily available to plants and easily absorbed.
- Worm bins can be used by apartment renters and condo dwellers alike, which gives people without backyards the ability to compost kitchen scraps and more.
- Worm castings contain a mucous deposited by worms, which helps to slow the release of nutrients and prevents them from washing away with the first rain or watering. Chemical fertilizers, on the other hand, are composed of synthetic nutrients that are washed away with watering.
- Worm compost also has a high concentration of beneficial bacteria and microbes, which helps to bolster the ecology of your soil. Chemical fertilizers (and pesticides) tend to kill beneficial creatures, hampering the health of your soil and a plant’s ability to fend off disease and pests.
- Many scientific studies have been done to prove that vermicompost can greatly benefit plants by improving seed germination, enhancing grown and development, and increasing plant productivity, especially when it makes up between 10% and 40% of the growing medium.
Setting up a worm compost bin
Although a worm bin will require a bit more structure than your backyard compost pile, it’s still relatively simple. Vermicompost bins can be constructed using several methods, of which there are generally three dependent on where you feed the worms and how you harvest the castings:
- Continuous vertical flow bins: These bins are made up of a series of trays stacked vertically. The bottom tray has layers such as bedding, worms, organic matter, then a thick layer of bedding, all stacked on top of something like chicken wire. Once the organic matter is all eaten, the worms will move to the next tray where the fresh food is. You wait until they’re mostly migrated and then harvest the compost.
- Continuous horizontal flow bins: Like the vertical flow bins, these use separate trays/bins by lining them up side by side, separated by chicken wire. Again, the worms are added to one side and fed there until full, then the food is deposited on the other side so that the worms migrate and the compost can be easily harvested.
- Non-continuous bins: These are the simplest to put together—you just layer bedding, then organic matter, then worms, then more bedding—with everything in one bin. It’s compact and quick to build, but does require a bit more energy when it comes time to harvest.
What type of worms to use
There are over 1,800 species of earthworms worldwide, but the most common worm species to use in vermicomposting is the Eisenia fetida, known also as the red wiggler, redworm, compost worm, or manure worm. These little creatures are hardier in a variety of temperatures (0oC and 35oC, or 55oF to 77oF)), can withstand a lot of handling, and they rapidly reproduce, making them ideal for changing environments (like worm bins where the food supply can be feast or famine at times).
Knowing how many worms you’ll need will depend on how much food waste you produce in the average week. In general, a family of four will generate about 7 pounds of compostable waste weekly, but the best way to determine this for yourself is to measure your food waste (by weight) for a couple of weeks, then average that by day. Red wigglers can generally eat about one-half of their weight in food per day, so if your family produces 7 pounds of food per week, that’s one pound per day, which means you’ll need two pounds of worms.
Worms can be purchased from a variety of vendors, though you should be sure to look for the red wiggler variety. Ask around your local community to see whether bait shops, garden centers, and natural living stores sell vermicomposting supplies, including worms. Many gardening magazines will also contain listings for worm dealers. CityFarmer.org maintains a list of worm suppliers throughout Canada and the US which should make your search a little easier.
You’re bound to find someone in your neighborhood who works with worms, and it’s always best to buy locally to avoid the greenhouse gas emissions associated with long-distance shipping. Sending worms through the mail can also be problematic as it can stress the worms.
If however, you can’t find a local provider, then consider online vendors such as the following:
Note: Most vermiculturists (people who work with worms for the purpose of growing populations) will require that you order your worms ahead of time and agree to pick them up on a certain date. They want to ensure that you receive a package of healthy, unstressed worms that haven’t gone without food for too long. Be prepared to receive your worms by having your bin already set up and ready to go before you bring them home.
What worms need to survive and thrive
Worms have a few basic requirements for healthy, productive lives, and these include:
- Bedding, usually composed of shredded newsprint, though you can also use things like leaves, cardboard (wax-free), burlap coffee bags, sawdust, hay, or peat moss—essentially any high-carbon material that’s low in both protein and nitrogen. Avoid high-gloss printed materials. Whatever you choose, be sure that it is highly absorbent (worms breathe through their skin and need a moist environment in which to do this) and not too dense with room for air movement so that oxygen can get in.
- Food source that is at least 50% water by weight. Ideally, the bin will have a moisture-content range between 70% and 90%.
- Sufficient aeration is required to make it possible for the worms to breathe oxygen. Poor aeration, too much grease, meat, and other factors can create an anaerobic (oxygen-deprived) environment which can quickly suffocate the worms and/or create toxic substances like ammonia. Providing ventilation to the bin and ensuring that bedding material is properly aerated is important to maintain adequate oxygen levels.
- Protection from temperature extremes and swings because, although red wigglers can survive freezing temperatures, they reproduce more quickly and consume food more efficiently when temperatures remain ideal (between 15oC and 20oC) and constant. High temperatures will cause them to want to leave, and if they can’t they will quickly die. Good places to keep your worm bin include your kitchen, garage (as long as it doesn’t reach freezing temperatures), laundry room, or patio (again, as long as temperatures are even and relatively mild).
- Ideal pH levels which are generally at 7 pH or higher. Coffee grounds (while enjoyed by worms) and other acidic foods can lower the pH, though the pH will generally drop in the bin over time. If too acidic, calcium carbonate can be added; if too basic, peat moss can be added.
Building your own worm compost bin
Making your own worm bin is relatively easy, though it will take the better part of an afternoon to get it all together. Here are the first two questions to answer:
- Choose the right bin type: Your bin should be able to maintain the right temperature and drainage. Metal is too conductive (will result in temperature extremes) and Styrofoam too insulating and can leach toxins, so avoid these two materials. Plastic works well and is easy to clean as long as it is opaque (not clear since worms don’t like light), and wood is fantastic as it can absorb some of the moisture.
- Determining the right size: You’ve already weighed your food waste over the course of a week or two and averages that out per day. Now take that number and choose a bin that has one square food of surface space per pound of food per day. Make sure that it’s not too deep as this can lead to odor problems.
Once you’ve selected your bin and determined the right size, you can get to building it. If you’re putting together a wooden bin, check out these Build a Wooden Worm Bin plans to make your job a little easier (modify the dimensions to fit your family’s composting needs). Regardless of what material you use, be sure to set up your bin with the following characteristics:
- Vent holes: Whether you’re using wood or plastic, you’ll want to ensure there are adequate ventilation holes in your bin. You’ll likely need holes along the sides and on the bottom as well (bottom vent holes also help to drain excess moisture). In all, you may need 8 to 12 holes that measure 0.25” to 0.5” wide, depending on the size of your container. You may find that additional holes are required if the bin becomes too wet.
- Fabric barrier: It’s a good idea to lay down a piece of fabric in the bottom of your bin over the drainage holes. This will prevent compost and worms from getting free. Old sheets work really well for this.
- Bin feet: You won’t want your bin sitting directly on the ground as this will prevent ventilation and drainage of excess moisture. You can prop your bin up on pieces of wood or build feet for it if you prefer.
Buying a worm composting bin
Today, there are numerous sites selling pre-packaged worm bins that come complete with ventilation holes and everything else you’ll need. You can choose from single-bin, stacked, and compost tea options, many of which can be purchased with a colony of worms ready to go. Here are some popular sites:
Setting up your worm bin for the first time
Once you’ve got your bin, it’s time to put everything together to make your worm bin ready to receive your worms. Here are the steps to follow to get your bin worm-ready:
- Lay down your piece of fabric to prevent the worms from escaping through the bottom ventilation holes.
- Moisten the bedding. Do this by putting dry bedding in a large container and covering it all with water. Let the bedding soak up the liquid over a period of 2 to 24 hours, then drain any excess and squeeze out the bedding so that it isn’t dripping wet.
- Place the bedding into the bin and fluff it up (it should not be a thick, matted mess). If time passes between preparing the bedding and adding the worms and the bedding has dried out, moisten it by misting it with water.
- Add the worms to the top of the moistened bedding as soon as you get home; they’ll quickly disappear as they strain for darker territory (they don’t like bright lights).
Your worm farm in action
How do you feed the worms?
The general rule is that you start by feeding your worms one-half of their body weight in food scraps per day (a half-pound of worms means you can feed them one-quarter pounds of food per day). As they become established, you can feed them more per day on average. Just test out various quantities to see how they do.
What do/don’t they eat or prefer?
The kinds of food your worms like will be much like those you would add to your outdoor compost bin or tumbler. These are the foods that work really well with worms:
- Vegetables and fruits (though nothing too citrusy)
- Pasta, bread, and other starchy foods
- Coffee grounds and filters
- Tea bags (without the metal staples)
- Egg shells (if crushed)
Each individual worm colony will have their favorites and foods that they dislike, so get to know yours by trying things out and seeing how long they take to get eaten. Generally, though, be sure to avoid these foods:
- Meat, fish, and poultry, including bones
- Fats and oils
- Non-organic things like plastic bags, rubber bands, staples, foil, glass, bottle caps, or twist ties
Feeding your worms will become a unique routine for your home. If your bin is healthy, you may be able to add food scraps to your bin daily, though many prefer to add food on a weekly basis instead to avoid disturbing the worms and minimize the work. Here are some tips for minimizing the hassle of adding food to your bin:
- Weigh the food and drain off a bit of the excess liquid if you have problems with moisture
- Take some newspaper (2-3 layers) and lay the food in the center, wrapping it up like a burrito
- Rotate where you put the food around the bin in some organized fashion
- Lift the bedding and place the package of food in the next available position
- Bury the food with plenty of bedding (add more if needed)
When first starting out, it is recommended that you begin slowly (in other words, don’t feed your bin to full capacity right away). Add a small amount of food material with some gritty things like dry egg shells or cornmeal, or coffee grounds. The worms will also be eating the bedding, so they won’t go hungry. Then add more food once the first batch has been eaten, and keep watching, matching their eating habits while giving the bacteria time to mature as well.
It’s also a good idea to keep a diary of what’s happening with your bin. You may want to track things like this:
- The position of the last food addition.
- How much food (by weight) you’ve fed your bin, including the date.
- Any special conditions you notice, like dry bedding, the presence of red mites, and whether the worms consumed the last batch of food.
- What foods were eaten and what’s been left behind.
Harvesting worm compost
There are many methods for harvesting your compost when the time is right (every 3-4 months, approximately). Here are three you may wish to try depending on your preferences, all of which start with a “starvation” period of about 10 days:
- Dump and sort: Perhaps the highest maintenance method, this one is also the most thorough. Gently turn out all of the contents of your bin onto a plastic sheet in a well-lit room or under a bright lamp. Wait 5-10 minutes until the worms bury themselves deeper into the compost, then brush away the top layer of compost until you start to see worms again. Wait another 5-10 minutes and repeat the process. Continue repeating these steps until you’re left with a pile of worms.
- Split-bin method: Start by moving all of the finished compost over to one side of your bin, then filling the emptied side with new bedding. Bury one package of food scraps below the bedding on the cleaned-out side. Gradually the worms will move to the new side (may take a few weeks) after which you can just scoop out the compost on the other side. Swap sides with each harvest.
- Onion bag method: In this method, fill an onion or delicates laundry bag with the worms’ favorite foods (apples, melons, etc). Place this bag in the next logical position in your worm bin and leave for a about two days, then carefully remove the bag and place it in a clean pail with some bedding. You’ll notice that a large number of worms will be in the bag. Start to scoop out the compost, starting in the opposite corner from where you placed the onion bag, moving toward that section last. In the end, you may need to do a dump and sort with the last remaining compost to get the last worms out.
Once you’ve harvested your compost, you can use your worm humus in a 4:1 soil to compost ratio when planting your spring garden. It can also be used as a top dressing for indoor and outdoor plants that have already been established.
Common worm composting problems
A worm bin is an ecosystem all on its own and must be tended to like you would any complex system that involves many moving parts. As such, problems can crop up, especially for first-time vermicomposters. Here are some of the more common problems faced by worm bin keepers and some suggestions for how to avoid and/or remedy them:
- If you live in a warm climate and keep your bin outdoors, be sure to shade your worm bin from direct sunlight to avoid overheating.
- If the bin develops an odor, add more high-carbon ingredients (newsprint or dead leaves) to counteract the presence of too much nitrogen (from greens like food scraps and grass clippings).
- If your worms are trying to escape, it means that some of the conditions in the bin are not to their liking. To avoid this problem, be sure to aerate the contents of your bin (give it a stir), add fresh bedding, reduce the quantity of food you add for awhile to decrease the moisture content, move the bin to a warm/cooler/quieter spot in your home, or adjust the pH if necessary.
- If your bin develops a mold problem, you may be feeding your worms too much, though this won’t harm them at all. Either take away some of the food so that the critters can catch up, or just avoid adding anything new for several days until you see that all of the food is gone. You can also take the lid off of the bin slightly for a short period of time to let some of the moisture evaporate, but not too long! A dry bin is deadly to your worms.
- You may be tempted to use your worm casting to grow seedlings, but don’t. Compost tends to be too rich as a seed starter and so should not be used for this purpose.
- Be sure to keep your cat from using your worm bin as a litter box.
- Avoid adding manure (horse, cow, pig) as it can heat up the bin and cook your worms.
Common vermicompost pests and what to do about them
Whenever you add decomposing food scrap to your bin, you’re creating an attractive lunch spot for pests like moles, ants, and fruit flies. Keep your worm farm healthy and intact by protecting your little workforce from predators and other unwanted pests by following some simple guidelines:
- If your bin is outside, ensure that you use wire mesh or paving material under the farm to prevent moles and other borrowing animals (that will eat your worms) from digging in.
- Put a cover over your vermicompost farm if your bin is out of doors to keep birds from carrying away your worms.
- Red mites can be a serious problem for worm farms because they are parasitic on earthworms (they suck blood and body fluid from your little critters!). Keep the pH at neutral or above to avoid these pests, which can be done by maintaining moisture levels below 85% or by adding calcium carbonate.
Whatever your pest problem, be sure not to use insecticides as these can harm the ecology of your worm bin. You can find out more about the potential pests that may inhabit your worm bin by checking out this guide to Worm Bin Critter Gallery.
Fending off fruit flies
Perhaps the most problematic for indoor vermicompost owners, fruit flies can be a nuisance, although they won’t harm your worms. The worst they’ll do is land in your morning coffee. But to get rid of these pesky creatures, here are some methods that you can test out in your own home:
- Remove all food attractants: Fruit flies love any rotting food source, so get rid of anything that will attract them. This can include things like dirty dishes, dishrags, and sink drains, food in the trash can, fruit bowls on the countertop (especially overripe fruit), fruit juice, anything fermented (vinegar, cooking wine, beer, and ketchup, for instance), counter and floor crumbs, food bits in fridge seals, under dishwashers and stoves, and the like. Be sure to keep all food and beverages in sealed containers, preferably in the fridge, maintain clean countertops, rags, sinks, and appliances, and seal up garbage and trash until it’s ready to go out to the bin.
- Prevent breeding grounds from forming: Moist places are prime areas in which flies breed, including wet garbage cans and even dirty mop water.
- Properly bury all food scraps in your bin: Unburied and exposed food scraps in your worm bin will be the perfect meal for fruit flies, so be sure to always bury your food waste below a good heap of bedding.
- Freeze food before putting it in the bin: Fruit fly larvae come into your home on fruit and veggies, but freezing the scraps will often serve to kill them before they can hatch. Just be sure to thoroughly thaw the food before putting it in your bin to avoid temperature shock.
- Vacuum the flies: If you can’t seem to get rid of the flies, take out your vacuum, quickly open the bin’s lid, and suck up the adult flies before they can fly away. Repeat this several times a day for a few days and you’ll soon have killed off the adult population so that they can no longer breed.
- Open a window or set the bin outside: If the weather isn’t too cold, either open a window near the bin or set the bin outside for a spell. The flies will fly away in a matter of minutes. Repeat this several times as with the vacuum trick.
- Use a thick stack of wet newsprint: Layer several sheets of newsprint the size of the top of your bin together, wetting each layer. Then place the layered sheets on top of the bedding to prevent the fruit flies from finding the food. Just be sure that your bin has vent holes in the sides and bottom to avoid suffocating your worms.
- Make a fruit fly trap: There are several methods of constructing traps, but you can find many of them in this How to Get Rid of Fruit Flies article.
- Worms Eat My Garbage by Mary Applehof (WormWoman.com)
- EarthWormDigest.org - A resource for all things earthworm
- BioCycle Magazine - Information on composting, organics recycling, and renewable energy
- CityFarmer.org - They have an imagistic, step-by-step guide to putting together a worm bin
- Earth911.com - They have a handy Worm Composting 101 video