Vermiculture: How to Worm Your Way into Composting

By Mary Karish

Contributing Writer

Many of us like the idea of composting, but lack the outdoor space, or live in a finicky neighborhood where composting shredded leaves is considered a cardinal sin. Fortunately, you can generate your own nutrient-dense compost in the comfort of your own home using nature’s master composters: worms. Experts call it vermiculture.

You might think all worms are created equal if your personal experience with worms is using them at the end of a fishing hook or watching them commit suicide on the pavement after a heavy rain. Worms represent a diverse group of burrowing organisms with more than 10,000 known species. While their life destiny is to decompose organic matter, not all worms enjoy an indoor lifestyle. Red wigglers (Eisenia fetida, to the science aficionados out there) are considered by enthusiasts as “the Mercedes of worms.” They are the most suitable worms for indoor composting. People often confuse them with red earthworms (Lumbricus rubellus) because it is almost impossible to tell them apart unless you are a nematologist (someone devoted to the study of worms). Red earthworms are known in composting circles and you typically find them in your soil. They can survive cold winters, which make them a threat to the ecosystem if they multiply in large numbers.

Red wigglers are ideal for indoor composting because they are shallow burrowers, living only in the top few inches of the soil. They are insatiable eaters and their diet consists of decaying organic matter. You only need about a pound (approximately 800 to 1,000 worms — you can count them if you don’t believe me) of worms for a healthy working population.

Stacking your leftover lettuce in the garden is not enough to get the nutrients to soak into the soil and make your vegetables grow. You need decomposers to break down the structure of the lettuce and transform the nutrients into a form that plants can absorb. But it is not just the worms doing the work, it is also bacteria. Bacteria are mini-recycling plants that reside in the worm’s gut. They produce digestive enzymes to decompose your lettuce.

Where do worms fit? Something amazing happens to food and soil that travels through the gut of a worm. As organic matter passes through the worm’s digestive system, it gets broken down, adding more bacteria to the mix. The end products of the worm’s digestion are castings: a nutritional addition to your indoor or outdoor soils.

Worms, like any animals, require food and shelter to keep them alive and happy. However, they differ from your standard pet care and attention. A major advantage of keeping worms as pets is that they love to munch on your kitchen garbage. They are, however, vegetarians. They enjoy vegetables, fruit scraps, bread, pasta, coffee grounds or filters. They also like browns, such as paper, dry leaves or junk mail.

Worms don’t like onions or citrus because it gives them indigestion, so avoid it. They cannot eat meat or dairy products because they lack the appropriate digestive enzymes to break them down. They do, however, like crushed egg shells because the shells provide a great source of calcium in their diet. Be sure to pile plenty of shredded newspaper on top to hold moisture in and keep fruit flies out. Finally, add one to two cups of garden soil or compost. It will inoculate your worms with beneficial bacteria to help them digest their food. Keep your worms well fed. They can eat up to half their weight per day.

The size and type of housing you provide will depend on your space and needs. Worms take up little space. You can keep a pound of worms in a 20-inch by 20-inch container, and they will be happy. Whatever container you select, it must have air holes to keep the soil aerated and the bedding moist.

Metal containers are non-absorbent but rust easily. They could also release heavy metal toxins into the bedding, and harm the worms.

Wood containers are absorbent with good drainage. However, use hemlock or west cedar because both are rot-resistant and won’t leach oils into the bedding.

Plastic containers are the most popular because they are non-absorbent, easy to clean and long-lasting. Worms like darkness, so get a container with a lid and drill holes for aeration. In about 90 days you can start harvesting the worm castings for your plants. If it is a one-time project, you can throw the worms and the castings onto the soil. The worms will have to fend for themselves until the cold kills them. The other option is to pick the worms for another round of composting. You will, however, realize you need the patience of Job to isolate the worms from the castings.

The best housing is stacked plastic bins forming layers of trays with a lid. Composters have nicknamed it “The Hilton Towers.” If you are a do-it-yourself builder, you can construct one or purchase it from many online sources. I bought mine from the Three Sisters, a Texas-based, family-owned company. Cover the first tray with newspaper, add soil or compost, food and your new pets. Place moist newspaper on top of the bedding and let your worms settle into their new house. Continue adding enough food to fill the first feeding tray. Once the tray is filled with food within an inch of the top of the tray, it is time to add a second tray with more goodies. If the space is more than an inch, the worms will not be able to journey up. Keep in mind these are small creatures, not acrobats.

After a few days, you will notice that some worms have started migrating to the second tray. Continue stacking trays following the same method. It takes the worms about 90 days to go through the food in the first tray before they completely travel to the next tray in search of a new food supply.

When it is time to harvest the castings, remove the lid. Place all the trays on the lid in the same order that they were arranged, except for the bottom tray. Put the bottom tray on top of the feeding trays, and expose it to light. Any stragglers that remained in the feeding tray will migrate into the feeding tray below where it is darker. Within an hour, you will end up with worm castings. The bottom tray now becomes a new feeding tray, and so on.

The worm population should double every 90 days, as long as you keep their housing temperature between 40 and 80 degrees. In the summer, move the Hilton Towers outside under the shade and in the winter in the garage.

The best part of harvesting worm castings is deciding what to do with this earthy black compost. You have two options: direct application or worm wine.

Direct application is adding it to your garden or potted plants. If you do not want worm eggs to end up in your soil, you can freeze the compost, ensuring nothing but nutrients will be transferred to your garden.

Worm wine is a nutritious liquid with increased beneficial microorganisms and disease-fighting capability. It is made by steeping worm castings and rainwater over a 24-hour period. You can apply it to the soil or as a foliar drench.

Worms are gardeners’ best friend. In return for your garbage they give you nutrient-rich compost.


“The Hilton Towers” and worms are available from My Three Sisters, 4941 Stockdick School Road, Katy, TX 77493; (972) 839-2188;

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