What is Vermicomposting?
Simply put, vermicomposting uses worms to turn organic waste materials into high-quality compost. The finished product is commonly referred to as worm castings or vermicompost, which can also be collected in a concentrated liquid state known as "vermicompost tea". Just like regular compost, vermicompost is a great all-purpose fertilizer rich in macro and micronutrients and beneficial microorganisms. Odor-free vermicompost can be applied to indoor and outdoor plants without the risk of fertilizer burn.
Do I have to use special worms for vermicomposting?
Believe it or not, there is a difference between the earthworms you see inching along the sidewalk after a rainstorm and the red worms preferred for vermicomposting. Red worms, red wrigglers or Eisenia fetida, are especially valued for their ability to process organic waste in a relatively short amount of time. Red worms will also thrive in the controlled worm bin environment you create for them and reproduce fairly rapidly as a result (worm populations can double each month in ideal conditions!). In addition, they can handle the frequent intrusions necessary for adding food and bedding material as well as the periodic disturbances that occur when harvesting castings.
Soil-dwelling earthworms on the other hand, will not fair well in an enclosed worm bin. In nature they spend most of the time deep in their burrows, coming to the surface only to collects leaves and debris that they need for food. As such, they aren't keen on environmental interferences and are best kept in the outdoor garden where they are excellent for turning and aerating the soil and incorporating precious organic matter.
The size of your worm habitat and the amount of waste being added will dictate the number of worms you need, however a 2:1 worm-to-waste ratio is the basic rule of thumb. For example, one pound of red worms is recommended as a good starting point for average households generating approximately one-half pound of kitchen scraps per day. This may not sound like a lot of worms, but they are efficient little workers with a surprisingly large appetite!
Eisenia fetida are available through a number of commercial resources and can be ordered at your local Worm's Way store, online at wormsway.com and over the phone at 800-274-9676. These are shipped directly from the farm to ensure live delivery, although they may not be available November through March due to cold weather.
Worm Bin Basics
Like compost bins, you can build your own or choose convenience with a ready-made red worm-composting habitat like the four-tray Sunleaves Worm Farm. Before you decide, consider the following:
• Size - the dimensions of your bin will depend on the amount of waste that gets generated from your household on a regular basis. This can be estimated by collecting your compostable kitchen scraps for the week and weighing in at weeks end; an average taken over several weeks will provide even more accurate results. The general rule is each pound of waste warrants one square foot of surface area.
• Temperature - red worms can tolerate temperatures from 40 to 80 degrees Fahrenheit although they prefer temperatures between 59 and 77 degrees Fahrenheit.
• Location - garages and basements are often favored for vermiculture projects as they are semi-temperate areas also convenient for regular trips to and from the kitchen.
• Moisture - because your red wrigglers actually breathe through their skin, it is imperative that they have a balanced moisture level. Maintaining the habitat about as damp as a wrung out sponge is best. Keep in mind that a moist environment does not mean stagnant as oxygen is also crucial for the survival of your worms. As such, homemade containers should also be equipped with ventilation for adequate air circulation.
• pH - ranging from 0 (acid) to 14 (base), the pH scale is used to determine the acidity or alkalinity of a substance. Just like plants, worms have a pH range that suits them best. Red worms can tolerate a range between 5-9 pH but prefer neutral to slightly acid conditions around 6.5-6. The pH of your bin can easily be determined with an inexpensive handheld pH meter.
• Darkness - worms desire dark living conditions, this is why they will retract if they are on the surface when you open your bin.
Bedding and Acceptable Food Materials
Bedding should be light and fluffy to allow good air exchange throughout your container and make it is easy for the worms to migrate through it. Recommended materials include: coffee filters and tea bags (with metal staple removed), tissues, shredded cardboard and paper, coconut coir and peat moss. Worms will also benefit from a handful of soil or dolomite lime because it will aid in their digestive process. As for acceptable contributions from the kitchen, vegetable and fruit scraps, plain bread and cooked pasta, crushed eggshells and coffee grounds are all suitable.
How to Harvest
About every three to four months, worm castings will be ready to harvest and if you've purchased a commercial bin, it should include instructions specific to that particular system. If you've created your own bin, you'll need to separate the worms (and any undigested food scraps) from the vermicompost to be harvested. One way to approach the task is to push all of the worms and decomposed materials to one side of the bin and fill the other side with fresh bedding and food. Give the worms a few days to migrate to the "new" side before harvesting. Because worms are sensitive to light, you can also shine a light into the container to send worms burrowing and collect the castings on the surface via a sieve or similar hand tool.
• Bury all food waste to discourage fruit flies and other insects
• Chop food scraps and bedding for faster decomposition
• If the bin starts to smell, there's likely more food than the worms can process. Stop feeding your worms, add more dry bedding and give the contents a good stir. If the bin just appears too wet, add dry bedding material, check drainage holes and be sure to empty the vermicompost "tea" collection tray on a regular basis.
What to Avoid
• Meat and dairy products of any kind
• Pet wastes
• Any item heavily coated in grease or oil