Indoor Worm Composting or Vermicomposting

Key points

• Vermicomposting (from the Latin word vermis meaning worm) is an efficient and enjoyable method for turning kitchen food scraps into a rich compost.
• Composting with redworms is becoming popular because it is easy and inexpensive to get started, can be done indoors in a small place and is odorless.
• Perhaps most important, it can be a fascinating and educational project for children.
• This web page is designed to help you start your own plastic worm bin that is 21" long, x 15" wide x 5 - 8 inches deep (approximately 2.2 sq. ft.).

How to begin and care for a vermicomposting bin

Getting Started

• Your home vermicomposting system will consist of a suitable container, moist bedding, redworms, and food scraps.
• Over a period of months, the food scraps and bedding will be digested by the redworms.
• The end product, vermicompost, contains worm castings (manure), decomposed bedding and lots of worms and tiny organisms both dead and alive.
• It is dark, crumbly, and safe to handle and makes an excellent soil conditioner and rich source of plant nutrients.

 Redworms

• Redworms, known also as red wigglers or manure worms, are surface feeders of dead plants and animals, commonly found in moist leaf litter and manure piles. They are well suited to vermicomposting because they thrive in confinement and will tolerate a wide range of conditions.
• Common garden worms and nightcrawlers, on the other hand, will quickly die off in a worm bin. Conversely, redworms do poorly in average garden soil.
• The two most commonly used redworm species are Eisenia foetida and Lumbricus rubellus. You can purchase them online as there are plenty of online sources.
• You will need a minimum of one pound of redworms for your small bin (500 - 1,000 worms). The redworms are 2"-4" in length and capable of consuming their own weight each day in raw organic matter. (One pound of worms will consume approximately one pound of raw matter.
• Measure the average amount of raw matter waste your family generates per day, then estimate the number of worms you will need.
• Worms live for about one year and reproduce quickly. Light colored cocoons are produced continuously which yield 2-3 baby worms in three weeks time.
• Redworms breathe through their skin and must be kept moist at all times. If more moisture is needed, use a spray bottle filled with water to mist the inside of the bin. 

Vermicomposting bins

• Plastic storage bins with lids are highly recommended for indoor use. They are inexpensive, durable, and lightweight. Your 2.2 sq.ft. bin can handle 2-3 lbs. of kitchen scraps each week. Avoid deep containers (over 15"); they are heavy to move and the bedding becomes compacted making it difficult for the redworms to forage for food.
• Drill a series of 1/4 - 1/2 inch holes in the bottom and lid of your container to encourage good air circulation through the bin. (Rigid plastic sometimes cracks when drilled. Use a sharp drill bit and drill slowly).
• Set your bin on top of bricks or scrap pieces of wood to allow air to enter the bottom of the bin. Place the bin on a plastic or metal tray to catch leachate (nutrient-rich liquid that percolates through the vermicomposting bin).
• Add the leachate to water when watering indoor plants.

Bedding for a vermicomposting bin

• Bedding provides your redworms with the cool, moist environment they need to thrive. Your redworms will tunnel through and digest the bedding along with the food scraps to produce vermicompost.
• They will not crawl out of their bin unless the bin becomes too dry or too wet. Hand-shredded newspaper (color pages included) or corrugated cardboard, ripped into thin strips, make convenient bedding materials.
• Soak 4 lbs. of bedding in a bucket with 1 and 1/2 gallons of water for a few minutes; drain off the excess water and place the bedding loosely in your bin.

Where to locate a vermicomposting bin

• When choosing a proper location for your worm bin, consider convenience and aesthetics, as well as the environmental needs of your redworms.
• They are most efficient at consuming organic matter and reproducing when they are kept moist and well ventilated in a temperature range of 55º-75ºF.
• Redworms are sensitive to light so keep your bin covered and out of direct sunlight. Basements, cool garages and kitchens are all good locations.
• Your redworms will die at freezing temperatures.

 Feeding redworms

• Redworms require a steady supply of food scraps to grow and multiply.
• Use a plastic container with a lid in your kitchen to collect food scraps. Feed your worms 2-3 times each week by burying appropriate food scraps directly under the bedding in different locations.
• The smaller the food scraps, the quicker they will be digested by your redworms.

 Items to add and not to add to a vermicompost bin

 Problems with vermicomposting bins

• Fruit flies – bury food scraps beneath the bedding to avoid fruit fly problems. Try flypaper on the lid underside or a sticky yellow card placed next to the bin to attract fruit flies.
• Odors may arise if too many food scraps are added at one time. Discard rotting food; avoid adding scraps for a week.
• Too wet – bedding becomes compacted and smelly; air is unable to flow through the bin. Check drainage holes, stir contents to increase airflow and add fresh, dry bedding.

Harvesting and using worm compost

• It will take your worms 6-8 weeks to produce a noticeable amount of vermicompost.
• The castings appear as small, dark, clumps that easily break apart.
  • There are several methods for removing the finished compost:
    •  Every 3-4 months, stop feeding for a few weeks and rake the compost to one side of the bin. Add fresh bedding to the other side; only add food scraps to the new bedding. Within a few months your worms will move into the new bedding allowing you to harvest the finished compost. Refill the empty end of the bin with fresh bedding and bury more food scraps.
    •  Every 3-4 months dump your entire bin contents into several piles on a sheet of plastic in a brightly lit room. The worms will dive to the pile bottom. Remove finished compost from the tops and sides of the piles.
    •  Every 3-4 months remove 2/3 of the bin contents for use in the garden. Add new bedding and slowly build up your worm population.
    •  Stop feeding after 4-6 months and allow the worms to completely digest all of the bedding and food scraps. The result is a fine, homogeneous compost (pure worm castings) with very few redworms.
• You can add vermicompost to seedbeds or planting holes or use it as a top dressing during the growing season for your favorite plants.
• Or try adding the vermicompost to your potting mix for indoor plants or outdoor container plants (no more than 1/4 by volume).
• Pure worm castings may have a high soluble salt content; use them sparingly and avoid direct contact with the roots of seedlings.

Additional resources

• Vermicomposting- North Carolina State University
• Composting with Worms- Oregon State University