Worm Composting 101 (Vermicomposting)

Words by Gregg Hayward
Photos by Ian Kennelly

Making a worm bin is fun and easy. It can help you divert a portion of your waste from the landfill while making it into a rich soil amendment called worm compost. Worm compost helps your plants, fruits and vegetables to grow healthy and sustainably. It’s a guaranteed conversation starter, and will likely change the way you think about waste. Here’s a fairly detailed guide to bring you through the whole process. (There is a plethora of worm bin info out there on the internet. We tried to boil it down to what you really needed to know here.)

I. Building the Bin

Step 1:  Supplies you’ll need:

  • 2 Plastic containers dark enough so that light can’t shine through. 18-gallon containers are a good size, or make one wooden box 18″ wide by 24″ long by 18″ deep…or whatever is convenient for you…try using scrap wood, like untreated pallets!
  • Drill or Serrated Knife – if using a drill, you’ll want a ¼” bit to drill drain holes, and a 2″ hole cutting bit for your fancy screening.
  • 2″ attic louvers – your fancy screening
  • Household screen – your budget-minded screening
  • Duct tape – to hold budget-minded screening in place
  • Paper  – newspaper is great, colored or not colored. No glossy ads, though, please!
  • Leaves – use leaves you find around your neighborhood (along fence lines is a good place to find ’em)
  • 5-gallon bucket
  • Water
  • Gardening Prong
  • Worms – ½ to 1 lb of Red Wiggler Worms (Eisenia Fetida) is what you’ll need. Check Craigslist, or ask around, maybe you can get some from a friend.
  • Tarp – used during harvesting…you can also use plastic trash bags cut on the long end and folded open. Hold them down in the wind with some stones.
  • People for harvesting
  • Beer/Organic Juices (for your harvest mates!)

Step 2:  Drill Drain Holes

Most of the food we eat has a large amount of water in it. That water needs to go somewhere as things break down. Drill holes at the deepest parts of your bin, 1″ apart. Use a ¼” drill bit, and drill from the inside of one bin, out. This is important, because if you drill it the opposite way, you’ll get a ridge around your drilled holes on the inside of your bin, making it difficult for liquids to drain. Remove any schmutz from the drain holes…a serrated knife works great for this. Now, liquids should be easily drained from the top bin. This dark brown water that drains out of your top bin is leachate (not worm tea as some mistakenly call it), that may or may not have been processed by your worms. Therefore, you wouldn’t want to put it on plants you might eat. You can spread it on your lawn or shrubs, but maybe not your prized plants, as you can’t be sure of the nutrient content of the leachate.

Drill 1/4inch holes at the lowest points of the bin. Drill from inside the bin out. Remove schmutz.

Step 3:  Drill/Cut/Screen Air Vents

Worms breathe oxygen, like us, except they breathe through their skin. Make sure your worm bin has a couple of vents to let fresh air in. You can screen this in using window screen and duct tape, or make 2″ holes and add in attic louvers. They look good and work well. Put your vents underneath the handles of your upper bin, and voila, you’ve got awnings for your windows…rain won’t drain into your bin, but nice fresh air will wisp through. 

Drill air vents beneath the handles using a 2 inch hole cutter bit. Pop your 2 inch attic louvers into the holes.

You can also use a knife, window screen and duct tape. Make the holes just beneath the lip of the bin.

Step 4: Drip Collection

Place the second, non-drilled bin on the ground, place some tin cans, plastic tubs, or whatever you got, in the middle of the bottom bin. Set the bin with the holes on top. Use cans or tubs so your vents are just above the lip of the bottom bin. This keeps a pretty tight seal between the bins, below the vents. This keeps pests out of the leachate water below, and reduces the water that would seep in here during a rain. You’ll want to empty this bottom bucket once a week, each time you feed your worms. Pour out the leachate on your grass, not plants you would eat. 

Place tin cans or plastic tubs between your bins. Use a height that puts your vents just above the lip of the bottom bin. This height should also create a modest seal between the two bins keeping pests out.

Step 5: Bedding

Red Wiggler Worms naturally live beneath leaves on the ground. Leaves and other organic matter are their home and their food. They eat mold and fungi and turn that into castings, the main ingredient in compost. So, to create as natural and productive an environment as possible for the worms, we need to create a mini environment that meets their needs. 

It’s simple: add moistened leaves and shredded paper. The leaves shed moisture, and paper absorbs it, making a nice, loose, damp environment for your worms. Use newsprint or junk mail, provided the paper is not glossy. Most inks used these days are soy based, and will not hurt you or your worms. Tear the paper with the grain (for newsprint, it’s from the top), and shred it into ½” to 1″ strips. Accumulate enough until it could fill about ¼ of one of your plastic bins. Gather enough broadleaf leaves to fill your container the rest of the way to the top when dry. Next, moisten the leaves and paper by dunking them in a bucket of water. Let excess moisture drip out, then toss them in your bin. Mix them all together until the leaves and paper are as damp as a wrung-out sponge. This is the ideal moisture for your worms, a key to a healthy worm bin. Your bin should now be filled up to just below the air vents with a nice, loose, damp mixture of leaves and paper, called bedding. 

Rip strips of newsprint in ½ to 1inch strips, making enough to fill one bin ¼ full. Gather enough broadleaf leaves to fill the bin the rest of the way. Dunk these materials in water, alternating leaves and paper. Mix so that the mixture is as damp as a wrung out sponge. Dump out any excess water from the bottom bin.

Step 6: Add Worms!

Now the part you’ve been waiting for: adding your new pets to your bin! They will quickly begin to burrow down into their new home. If you are getting worms from a friend, add a scoop or two of their compost-in-progress to your bin. This inoculated (filled with micro organisms) compost will quickly sprout other helpful organisms in your bin which will help break down scraps.

II. Caring for your Worms

Just like any animal (including humans) basic needs must be met for your new pets to survive and thrive. Here’s what you need to remember to keep your worms happily munching on your scraps. It takes about 4-6 months to go from a bedded-worm bin to a completely finished worm-compost-filled, ready-to-harvest bin.

Worm Needs

Food: Worms eat the mold and fungi that grow on fruits and vegetables, with a few exceptions. (See below for details.) Start your worm bin off with a fist full of food scraps each week, then slowly ramp it up to eventually 32-50 oz. of fruit and veggies scraps per week, per bin (around the size of a large yogurt container). 

Use an old yogurt container to collect your kitchen scraps, and place that in your freezer. This will reduce pests, and help the material break down faster, as the plant-cell walls stretch and break when frozen. Number the corners of your bin and feed at the very bottom of the bin, in a different corner each week. That way, you can check back in on how the worms are eating. If after a month, some food is still remaining, feed them less, especially of whatever food remained. Feeding at the bottom of the bin allows the leaves and paper above to insulate smells, puts the food right where the worms are, and discourages pests.

Worms Eat: leaves, paper, fruit, veggies, tea bags, coffee grounds, bread, some citrus (not tons)

Worms Don’t Eat: meat, dairy, oil, bones, plastic

Water: Keep the bin as damp as a wrung out sponge. Water should not drip out when you squeeze some bedding in your hand, but it should leave your hand damp. Worms breathe through their skin, and are 90 percent water, so a moist bin is a productive bin. Generally, your fruit and veggie scraps help keep the correct amount of moisture in the bin. But if things get too dry, add a bit of water. Spray it in and work it into the bin material. If your bin gets too wet, dump out any excess moisture from the bottom bin, and if you have pools of water in the top bin, look at how it’s draining…add more holes, make sure the holes are clear of plastic and drilled from inside the bin out at the lowest points of the bin. Add a bit of dry paper to absorb water if needed.

Number the corners of your bin. Feed in a different corner each week. Bury your food scraps at the bottom of the bin, and at all times keep enough leaves and paper on top to reach just below the vents.

Shelter: Worms are photophobic, meaning that they are naturally afraid of light. So, you want to make sure you are using a bin that light can’t get through. As the worms break down the materials in the bin, you can add more leaves as necessary. Adding more leaves also acts as an insulator for temperature and smells.

Temperature: Worms like the same temperatures we do. Ideally 70 degrees. Their metabolism slows as the temperature dips, so they will be less productive down to 40 degrees. Above 100 degrees and your worms will start to die quickly. Keep your bin in the shade, or even better in a basement or cool garage. A bin in the sun when the air temperature is above 80 degrees is a cooked bin.

Air: Worms breathe through their skin. Every month or so, loosen up the materials in your bin with a gardener’s prong. This will oxygenate and loosen the environment they live in.

Quiet/Vibration: Worms have few senses, and rely very heavily on their sense of touch. Do not place your bin in a high vibration area, such as near a washing/drying machine.

III. Harvesting Worm Compost

Step 1. Invite Friends

Harvesting takes a little time on a sunny day. We highly recommend spending that good time with your friends, and they can help!

Step 2. Tarp Surf

You’ll be using a tarp anyway, so this is probably a good idea.

Step 3. Use tarp to help sort your compost

Spread it out in the full sun and put rocks on the corners to keep it from floating away. You can also use trash bags cut at the seam as a tarp as well.

Step 4. Place finished worm compost in heaps the size of a dish on the tarp. 

Let these heaps sit there for five minutes or so. Hang with your friends. Your photophobic worms will dive to the bottom of these piles.

Brush off the top inch, and an inch around the side of each pile. You’ll find few worms, as they dive to the center of the pile. Separate the compost from the worms, and put them in two separate containers. Brush off another inch every five minutes. Place any “overs” that haven’t broken down all the way in a third container.

Step 5. Brush the top inch off each pile, and around the sides and sort through it. 

Remove any worms, and any “overs…” (things that haven’t broken all the way down). Place your worms in a butter or yogurt tub with some very damp leaves and paper. Put the “overs” in a bucket, or a corner of your tarp. Place your finished compost in another corner or bucket. Continue this process, every five minutes, going through your piles. As you go on, you will find more and more worms as you get down the bottom of the piles. Sort through all of your compost in this manner. Plan on giving yourself two hours to get the job done with two or three friends. Doing this process on a table in the sun with the tarp on top is a fantastic idea.

Step 6. Share the Stoke! 

Give worms to your friends! You only need ½ to 1 lb of worms to start a bin. Give your friends worms to start their own bins! Give them some “overs” too.

Step 7. Put Your Worms Back to Work

Re-bed your worm bin, just as was explained earlier. This time, add in any of your “overs” as well. This will help jump start your bin. Go back through the whole process again and again! Each time, you’ll learn more, reduce waste, and make great compost for your plants, fruits and veggies. If at some point you wish to stop composting, give your bin to a friend, or put an ad up on Craigslist. Chances are it will go fast. Please do not dump your worms in a pristine natural environment.

Over your worms? These worms are endemic to much of the populated places in the United States, but are not always native. Don’t introduce foreign species into places they don’t belong. Give a quick call to your local cooperative extension department in your county and they will let you know what to do with your worms if you can’t find a home for them. Please don’t dump them in the forest.

IV. Using Worm Compost

Worm compost is strong! Some say up to seven times as strong as traditional backyard compost, as the worms continually reprocess and concentrate the compost. You only need to use a small amount of it to help your plants grow. Use it wisely: a 5-gallon bucket of worm compost can fertilize a 25-square-foot garden!  Here’s how:

Mixing with Potting Soil:

A general recipe for potting soil is:  1 shovel of regular backyard compost, 1 shovel of sand, ½ shovel of perlite.  Add ⅛ of a shovel of worm compost as well if you’d like. 

When Planting:

For small garden plants, mix a tablespoon with existing soil taken from the hole where you will plant. Place that back in the hole, then place your plant on top of this mixture, backfill and water. For larger plants and shrubs, mix ⅛ of a shovel full with 1 shovel full of loose topsoil taken from where you are planting. Place this mixture at the bottom, place the plant on top, backfill and water.

Fertilizing plants:

When you see flowers on your fruit and veggie plants, dig a small trench to the depth of your second knuckle around the base of your plant, two or three inches from the base. Sprinkle in two to three tablespoons of finished worm compost, cover that over and water. The nutrients will go right to the roots, and all that energy will be put into developing delicious fruit. 

Mix into existing garden soils:

After tilling your garden for the spring, or upon resting your garden for the winter, or between seasons, place compost in the soil where you intend to plant. You could mark rows using popsicle sticks, dig a small trench, and sprinkle in 3-4 tablespoons per foot of trench and cover that over. Plant in the same rows next season.

V. Alternative Bins

There are many different types of worm bins out there. If you want to avoid plastic, you can make a simple box out of non-treated pallet wood. You’ll keep pallet wood out of the landfill, and have nice natural bin. There are also many commercially made bins available.

VI. Worm Compost FYI 

Here are some facts you can share with your friends, family and whomever, when they ask why you have worms:

Worms Compost(ing):

  • manages waste right at home instead of sending this heavy, moisture laden waste on the long trip to the landfill.
  • fights climate change! Food waste in a landfill releases methane gas, which is 21x stronger as a greenhouse gas than the CO2 produced through composting.
  • can take the place of many of the chemical fertilizers you’d have to use, it helps plants grow, but can do so much more for your soil than fertilizers:
  • is rich in nutrients that help plants, fruits and veggies grow (unlike fertilizers, compost releases these nutrients slowly for sustained growth, while increasing the overall fertility of your soil).
  • is full of organic materials that are still in process of decomposing (like flecks of the pepper stem for example). These materials absorb water and release it slowly, this helps plants survive drought.
  • it’s organic matter’s moisture absorption helps reduce erosion. On the other end of the scale, compost releases water slowly, helping plants survive drought. Organic matter in compost also increases pore space in the soil, which helps oxygen get to roots, worms wiggle around and the tilth of your soil to improve.
  • has micro-organisms living in it. These microbes, when put into the soil with your worm compost, spread out and begin to break down other organic matter in the soil. They are also able to process nutrients in the soil into forms that are easier for your plants to absorb.
  • does all of this naturally. Badass!

VII. Troubleshooting

A worm bin is a living ecosystem, and as such, it changes all the time. That’s one of the most interesting things about keeping a worm bin: you are not sure what to expect each time you open the bin. We manage the ecosystem so that worms do most of the work for us. When food, water, air, or any other factors change in the bin, the ecosystem changes as well. Other organisms will do the decomposing, usually at a slower pace. To keep your worms happy and working well, here’s how you can solve some issues that may come up with your bin: 

(Most important is to remember that the ecosystem, or science experiment you have, is always changing. You will learn more from your mistakes than your successes. Have fun, and share your knowledge with others!)

The bin stinks!

Chances are, the bin is either too moist, there is too much food in the bin or the bin isn’t getting aerated enough. A healthy worm bin should smell like the forest floor after a rain. Make sure to empty off any excess water, or remove any excess food. You can mix in dry paper as well to absorb some moisture. Break up any clumps of paper that might exist in the bin. Run your gardener’s fork through all the material. This gets air into everything, which in the long run helps as aerobic organisms break down waste quickly with little smell. 

Worms aren’t eating what I feed them

Figure out what they are/aren’t eating, and decrease what they are not enjoying. If most everything is left and it’s early in the cycle of your bin, feed your bin less in general. The appetite of the bin will increase as the population of worms increases over time.

My worm population is decreasing

Go back and take a look at the “worm needs” section of this guide. If one of the worm needs is amiss, this will have an impact on the worms. Also, look for worm competitors/predators  in your bin, such as ants and slugs. Remove any slugs you see. If you have an ant problem, take the lid from your second bin, and place that upside down beneath the bins. Fill the “moat” that this forms around the bin with water. Refill this every couple of days. This will keep the ants away. You could also try putting a mixture of chili powder, soap and water in this moat. It will evaporate leaving the chili behind, discouraging pests.

Fruit Flies

Even the best worm composters get them. They are simply another decomposer. They are showing up because they can smell decomposing fruit and veggie waste. Make sure you are burying your waste at the very bottom of your bin, and that you are covering it deeply with leaves and paper. Leaves and paper should always fill to just below the air vents of your bin. Add more as needed. Make sure to empty your bottom bin of leachate weekly.

Make a fruit fly trap by putting 1″ apple cider vinegar in a jar with a drop of dish soap, and mix it up. Cover the top of the jar with plastic wrap, held in place by a rubber band. Poke holes in the plastic wrap with a ballpoint pen. The worms will fly into the jar, drink the vinegar and not be able to fly out. Place the trap above your bin. Works great in kitchens too!

VIII. Conclusion

That’s it. Whew. We tried to make this as much of a one-stop worm-compost shop as possible. Please share this resource with others! Got a question, or success to share? Email us! Best of luck with your new pets, and thanks for doing your part to reduce waste and help the environment.