The Guide to Black Gold: how to build and manage a worm composting bin in your home

Why Worm Composting?


The EPA states that more than 23% of wastes generated are compostable. Together, we can significantly reduce the amount of wastes that goes to landfills while also improving the food production capacity of Somerville by ever improving the soil quality in gardens throughout the city.


Many Somerville residents are unable to compost in outdoor piles due to space limitations or landlord requirements. If you experience these barriers to composting, indoor worm composting is a great option for you!


Given Groundwork’s mission, we want to encourage residents to engage in composting to reduce the waste stream to landfills and the city. This manual provides a step-by-step guide to producing worm compost in your home.


In addition, if we can build political will over time, it is possible that the city will adopt a municipal compost pickup as many cities throughout the country have begun to institute. San Francisco is one excellent example. You can learn more about San Francisco’s municipal composting program at


Before You Begin


Vermiculture, or worm composting, allows you to compost your food waste faster than you ever imagined, while producing the highest quality compost and fertilizing liquid. Best of all, it’s self-contained and nearly odorless! In order to keep your system working optimally, there are a few quick things to know before you begin to compost with worms in your home.


This is a guide for composting indoors. Creating a worm bin is like creating a tiny ecosystem and maintaining a healthy worm bin requires protecting this ecosystem from the extremes of New England weather. Your bin will function best when you’re worms are happy in their simulated underground environment. It should be dark, moist, and cool (40-80º F). Your bin should never be allowed to freeze. Find a tucked away corner of your home in which to construct your worm bin.



What do worms like to eat?

A balanced diet makes for a healthy bin, healthy worms and a great finished product.



Do Compost Don’t Compost
Raw Fruit and Vegetable Scraps Citrus or Onions (contain volatile oils that are abrasive to worms)
Eggshells Meat or Fish (can cause smell issues and attract undesirable insects)
Coffee Grounds and Filters Oily foods
Tea Bags (metal staples removed) Dairy Products



Collecting Materials


The Worms!

The species of worm most often used for home worm composting are called Eisenia foetida or more commonly, “Red Wigglers.” These are the worms provided with this guide. Red Wigglers are about 3 inches long, mainly red along the body with a yellow tail. Over time, this species has become especially adapted for decaying organic material. Unlike your everyday night crawlers, they live well in close, highly populated conditions, and reproduce quickly. In addition, these guys are very healthy eaters – Red Wiggler worms can eat about half of their weight in food every day! These worms can be purchased from Groundwork Somerville or can be found from a variety of sources online. Getting high-quality worms is the very first step in the success of your bin. For this sized bin, the recommended starting number is 1000 worms (about 1 pound), but you can start with less and let your worm population grow.


The Bin!

There are many recommendations for how to make your own worm bin and even more ready-made products available. Our guide focuses on building a system using heavy-duty rubber storage bins which are readily available at your local hardware store, fairly inexpensive, easy to use, and durable. In addition, many rubber bins come in stackable varieties which makes it easy for you to build a several-tiered system over time as you become a worm composting expert.


To begin, purchase a 10-15 gallon bin with a cover to prevent light from getting in and to prevent the compost from drying out.. This size bin will accommodate the organic waste of about two adult avid veggie eaters. Bigger bins do allow for you to add more food scraps each week, but are not advisable for beginners as they are slightly harder to manage. This is a great size for a first-time worm composter. You’ll also need to find something that can work as a catch tray for the bin to sit on to collect any of the highly-fertile liquids that drain from your bin. A large, old cookie sheet works well for this. You will also need 2-4 bricks or cinder blocks to elevate your bin over the tray to allow for necessary drainage.


Building Your Bin

  • Take a look. Place your catchment tray on the floor where you expect to store your bin. Use the bricks to elevate the rubber bin and cover it.


  • Ventilation and drainage holes. Your bin will need adequate air and moisture management in order to maintain an ideal environment. To do this, you will need to create several 1/8” holes. Depending upon the thickness of the rubberized tub you purchased, an electric drill may be helpful in making these holes.
    1. Drill 2-4 holes in the cover of your bin for vertical airflow
    2. Drill about 10 holes around the sides of the bin for lateral airflow.
    3. Drill 4-6 holes in the bottom for liquid drainage. (These are the most likely to clog, an unfolded paper clip works wonders in unclogging holes and restoring flow)


  • Create the environment. Once all the holes are drilled, fill the bottom of your bin with thin strips of unbleached corrugated cardboard, paper bags, shredded newspaper, straw, dry grass (without chemical treatment), or some similar material. This layer should be about 4-6” deep. These materials are called “bedding” and are essential to your worm bin environment since they absorb excess moisture, help to balance the carbon-to-nitrogen ratio, increase airflow, and help to create a safe habitat matrix for the worms. Moisten the bedding with water.


  • Add the worms! If you purchased worms from Groundwork Somerville, your bag has both the worms themselves and some biologically-active soil, which are both essential to starting a new bin. Gently add all the contents to your bin, attempting to distribute in an even layer. If you are obtaining worms from elsewhere you will need to add an organic soil or finished compost of some sort at this stage.


  • Feed the bin. Do a light first feeding. A 1-2 cup feeding of small pieces of vegetable scraps is ideal for this – spinach or lettuce alone work great if you have some that’s already starting to turn. The worms are in shock having just moved into a new home, so this careful, light feeding of food helps to ease the transition. Layer this on top of the worms and cover with a thin layer of moistened bedding.


  • Give it time. Let the worms acclimate for about 4 days before beginning to add food scraps to your bin. After that, you can start feeding more regularly.

Maintaining a Healthy Composting Environment


You should add food to the bin about once per week. A good quantity to aim for is 2 quarts per week of food scraps. One strategy is to keep a small container in your kitchen for collecting your compostables in between feedings. This helps you keep track of how much you’re adding to your bin. Every time you add “greens” (food scraps) to your bin, add about an equal proportion of “browns” (bedding materials). In addition to keeping the moisture of your bin in balance, keeping browns and greens in the correct proportion will help to increase the fertility of the final product of your bin – nutrient-rich castings!


Monitor your bin every time you add new compost for signs of distress. The most common signs of distress are excessive odor and worms climbing up the sides of the bin. A correctly maintained bin should be almost odorless and though worms can escape almost anything, a healthy environment will keep them contained without issue.


If your worms are showing signs of distress…

  • Use an unfolded paperclip to reopen all of the air and drip holes in the bin to make sure that proper air and moisture flow are maintained.
  • Check to make sure that there are no standing pools of moisture in the bin.
  • Check to make sure that the bedding isn’t excessively dry. If so, sprinkle a small amount of water and ensure that the cover is properly attached and the bin is out of direct sunlight.
  • Make sure that you haven’t fed your bin anything that is potentially irritating.
  • Reduce the volume of food you provide your bin for a few weeks.


Check your population regularly. If it looks like you have too many worms in your bin, you probably do. Consider giving some worms away to a friend or building a multi-tiered system as described before. Overpopulation is a sign that your bin is thriving, but as in any natural system can introduce undue stress. Work on improving the situation quickly.


Harvesting Your Finished Compost


After you have fed your worms for three to six months, you’ll see some worm compost in the bottom of your bin. You can harvest what’s there, or wait until your bin is nearly overflowing. No matter which method you use, some worms will remain in the compost. Worms put in the garden with the compost will not live long, but your main goal is to reserve enough worms to re-start your bin. You can’t save every worm! Here are a few methods for separating the worms from the compost.


Method #1: Most of the uneaten food, bedding and worms will probably be in the top third of your bin. Remove this material, worms and all, and put it aside to start a new bin. Remove the remaining material from the bin for use as worm compost. Put the uneaten food, bedding and worms back in the bin, and resume feeding and maintaining your bin.


Method #2: Spread a sheet of plastic out under a bright light or in the sun. Dump the contents of the worm bin and build a few cone shaped piles on the sheet. Gently remove the top layer of each pile until you see worms. To escape the light, the worms will dive deeper into the piles. After repeating the process every 20 minutes or so for a few hours, you will be left with a wiggling pile of worms. Save your compost and return the worms to their bin and fresh bedding immediately.


Using Your Worm Compost

Using your finished product will help your plants thrive by adding plant growth hormones, beneficial microorganisms, humus and nutrients to the soil. Vermicompost is lumpy and clay-like when removed from the bin. Let it sit in a plastic bin or bag away from rain and sun for 1-4 months and it will transform into a fine-grained product! Sprinkle a layer at the base of indoor or outdoor plants, making sure compost is not piled up against plant stems. Cover with soil or mulch to conserve moisture and retain nutrients.. You can also blend worm compost up to 20% into potting mix or garden soil.


An excellent liquid fertilizer can be made from the castings by adding water until the mixture looks like weak tea. African violets and other plants that like being fed from the roots, just love this mixture. Moisture drained from the worm farm’s bottom crate is also a good liquid fertilizer, but it too should be diluted.
Worm Composting Resources


Worm Composting Supplies Online:



Worms Eat My Garbage, 1982

Mary Appelhof

Definitive guide to setting up and maintaining a worm composting system.

Compost, By Gosh!, 2002

Michelle Portman

Combines Dr. Seuss-like poetry with child-friendly illustrations to explain the vermicomposting process to even the youngest reader/listener.

The Worm Cafe: Mid-scale Vermicomposting of Lunchroom Wastes, 1999

Binet Payne

A next-level guide to scaling up home worm composting to impact whole communities.


Worm Digest; (541) 485-0456.

Forum, books, publications, and links.

City Farmer, Canada’s Office of Urban Agriculture

California Integrated Green Waste Recovery Board

Fact sheets, supplier list and links.

Santa Cruz County Guidelines for Home Worm Composting

Groundwork Support:

Email with any and all questions or concerns about your composting efforts!











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