Vermicomposting – Composting with Worms
What is Vermicomposting?
Vermicomposting is composting with worms. The vermi in vermicomposting comes from the Latin word for worm – Vermis. Vermicomposting differs from normal, or microbial, composting. In vermicomposting, worms do most of the work breaking down organic matter instead of fungi and microorganisms. There are other differences: vermicomposting bins do not heat up, and bins do not need turning. You do not even have to touch a worm.
Why Compost with Worms?
The average American creates 4.3 pounds of waste each day. Nine percent of this is food waste, 14 percent is yard waste and 32 percent is paper and paperboard. All of this is organic matter that can be composted or vermicomposted. By removing the organic portion of the waste stream by home composting, residents can reduce the cost of municipal solid waste collection and disposal, prolong the life of landfills, add value nutrients and organic matter to soil and reduce the amount of chemical fertilizers used in gardens and lawns.
Kinds of Worms
A number of different species of earthworms have been used in vermicomposting, but the only one currently recommended for use is Eisenia fetida. These worms go by many common names, but the two used most often are Red Wiggler and Tiger Worm. They are called Red Wigglers because they are reddish in color and squirm around when agitated or exposed to sunlight. They also are called tiger worms because when they stretch, tiger worms show alternating red and buff colored bands. Eisenia fetida is the only earthworm with this tiger stripe pattern.
Red wigglers reproduce quickly, are naturally adapted to life in a bin and are voracious eaters. They are relatively small – less than three inches long when not stretching. They prefer to live in dark, wet places and tolerate temperatures from nearly freezing to 80 F. They work best at temperatures from 60 F to 75 F, and begin to die when their bin temperature exceeds 85 F.
Purchase Red Wigglers or Tiger Worms from established worm farms. They also are sold over the internet and can be shipped to any location. Do not buy red worms from bait stores, as these are usually other types of worms, many of which are invasive species. To start a worm bin, buy one pound of compost worms per square foot of bin surface.
Kind of Bin Needed
There are several types of commercial bins available. Homeowners can choose to make their own from a variety of materials, such as plastic storage boxes, washtubs and wooden crates. One man even buried an old refrigerator in the ground to use as a worm bin. The container should have a secure and removable lid to keep out flies, cats and rodents. Ventilation holes around the lid and top of the bin should be small to keep out flies. Larger (1/8-inch) holes drilled in the bottom will relieve excess moisture. Place a large tray under the bin to collect seepage. The excess moisture seeping out of the bin is called leachate or vermicompost tea. It is excellent liquid plant food.
The bin should be large enough to accommodate the amount of food produced by the household. A good rule of thumb is 2 square feet of bin surface area per person contributing to the bin. The goal is to spread a thin layer (1/4 to 1/2 inch deep) of food scraps per week. For two people, a container 2 feet by 2 feet should do. The bin should be 12 to 24 inches deep.
What do Worms Eat?
Worms eat just about any kind of organic matter: coffee grounds and filters, tea bags and tea leaves, vegetable and fruit scraps, breads and grains, uneaten cat and dog food. Do not feed greasy food, meat and dairy products or pet waste. Worms do eat this stuff, but flies and maggots eat it faster and will take over the bin. Worms do not eat plastic, rubber, cellophane, bones or twigs. They will ingest and pass egg shells if they are ground into small pieces.
How are Worms Fed?
Worms like a higher carbon diet than microbial composting. One way to manage this is to spread the “green” material (food scraps, coffee grounds, etc.) thinly across the bin and lightly cover with a layer of “browns” (dried fallen leaves or shredded paper). Spread the next layer of greens on top of the browns. Keeping a layer of higher-carbon brown material over the quickly decomposing greens reduces odors and flies. It is a great way of getting rid of junk mail too.
Table 1. Troubleshooting Guide for Worm Bin Problems
|Rotten Odor||Too much food
Food exposed to air
Greasy or meaty food
Not enough air
|Cover exposed food with brown material, stop feeding for a week
Cover exposed food with brown material
Drain moisture, fluff material
|Bin attracts flies||Too much food
Air holes too big
Bin has become acidic
|Cover exposed food with brown material, stop feeding for a week
Cover holes with netting
Remove citrus peels
Sprinkle top of bin with ag lime, fluff bedding
|Bin full of Sow Bugs and Roli Pollies||Woodlice thrive in the same conditions as compost worms||Clean the bin. Spray with Pyrethrin before restocking with worms|
|Mold is forming in bin||Bin had become acidic||Remove citrus peels, sprinkle top of bin with ag lime, fluff bedding|
|Water running out of bottom||Bin is too wet||Drain, add dry bedding or brown material, fluff bedding|
|Worms escaping or dying||Bin is too hot
Bin is too dry
Bin is too wet
Not enough bedding
|Move to a cooler area
Spray water to moisten, fluff
Drain, add dry bedding or brown material, fluff
Add bedding material so the worm bed is 6 to 10 inches deep
In nature, composting worms eat organic matter on wet forest floors and transfer nutrients downward through the forest litter. The community of worms creates a bed of fluffy material they wiggle through and aerate every day. When starting a bin, put some starter bedding in the bin before adding worms. Eventually the bedding and food get mixed by compost worms and become vermicompost. Bedding should be lightweight, biodegradable and retain moisture. The best bedding is old compost. Other bedding items are shredded paper mixed with soil, peat moss and coconut fiber (coir). The bedding should be moist. Wet it, then wring out the excess moisture and fluff it up. Spread the bedding evenly in the bin 6 to 10 inches deep.
Where to Put the Bin
Keep in mind the optimum temperature range of red wigglers (60 F to 75 F) when positioning the bin. Basements and cellars are ideal for year-round vermicomposting. Many people keep a small bin under the kitchen sink or in a laundry room, but do not over-feed, since this attracts flies. Attached garages are fine in winter, but are too hot during Oklahoma summers. During summer, place the bin outside in the shade or on the north side of the house. Add water to the bin to keep it cool and moist in the summer. To keep the bin thoroughly cool, add ice in a separate tray above the bin and allow cool water to drip down onto a layer of shredded paper above the worm bed.
Harvesting Compost and Worms
Compost worms turn feed and bedding into rich, dark compost in two to five months. Harvest vermiccompost two or three time per year. Here are two ways to harvest worms and compost:
- Dump the bin into several small piles onto a plastic sheet under a bright light or in full sunlight. Worms hate light and will retreat to the center of the pile. Every few minutes brush compost off the top of the pile. Within half an hour, nothing will be left but little balls of worms. Return the worms to a bin full of fresh bedding and begin to feed. Use the compost in the garden.
- Do not feed the bin for about a week. Make a small mound in the middle of the bin. Soak this mound with diluted molasses. The worms will migrate towards the molasses in about two hours. Remove the ball – worms, vermicompost and all – and use to start a new bin. Start feeding the new bin and use the remaining vermicompost in the old bin in the garden. It may take two or three times to remove all of the worms from the old bin, but you will be left with about half of the contents of the old bin to use in the garden.
Vermicompost in Gardens and Landscapes
Vermicompost can be used immediately or stored for later use. It is very rich in nutrients. Dry food-scrap-shredded-paper based vermicompost has a fertilizer value of 1 to 7 percent Nitrogen, 0.5 to 1.5 percent P2O5, and 1 to 2 percent K2O. Carbon-to-nitrogen ratio of mature vermicompost is less than 15-to-1.
As a soil amendment: mix ½ to 1 inch of vermicompost into 6 inches of soil.
As mulch: Spread ½ to 1 inch of vermicompost beneath canopy of growing plants out to the point where rain drips from leaves.
In a seedbed: Place ½ to 1 inch of vermicompost in the bottom of the furrow. Place seeds on top of vermicompost.
In potting mix: use 1/4 to 1/3 vermicompost by volume.
Vermicompost is a stable product, but it does not go through a heating process. Therefore, the 90/120 rule should be followed when using vermicompost in vegetable production: Vermicompost application should occur 90 days before harvest of vegetables whose edible parts do not come in contact with the soil. Vermicompost application should occur 120 days before harvest of vegetable crops whose edible parts come in contact with the soil.
There is no restriction on applying vermicompost to ornamental and other non-edible plants.
Once established, a vermicomposting bin requires little attention. However, problems can arise. The troubleshooting table can help diagnose and cure problems.
Hamilton, Doug. (2016). Oklahoma Cooperative Extension Service publication. BAE-1528, The Basics of Vermicomposting.
Hillock, David. (2016). Oklahoma Cooperative Extension Service publication. HLA-6448, Backyard Composting in Oklahoma.
Douglas W. Hamilton
Waste Management Specialist