By Betty Debettencourt, UC Master Gardener
Vermicomposting is the process of using worms to decompose vegetable matter. The resulting worm compost or worm castings is a nutrient rich soil amendment, which improves soil structure, fertility, and water-holding capacity.
Worm Bin Components
- Worm bin - can be purchased or homemade, constructed of wood or plastic. Requirements include good air flow, drainage, and a location protected from extreme temperatures. The bin can be a simple storage container with ¼ inch holes drilled in the bottom and sides. The size depends on the amount of food scraps, but the optimal depth should be limited to 8-12 inches. Worms prefer darkness so secure a lid to the bin.
- Bedding - serves to hold moisture, bury food and is an additional food source. The material should be light, fluffy and non-toxic to the worms. Examples include shredded newspaper, decaying leaves, coconut fiber, wood chips, and peat moss. Do not use bleached or printer paper or paper with colored ink. Bedding should comprise at least 50% of the organic matter.
- Worms- Red worms (Eisenia fetida) are the most common worms used for vermicomposting as they have desirable features: consume organic material quickly, reproduce well, prefer to live near the surface and do not burrow. They are available at bait stores or online. The number of worms needed will depend on the container size. Note: earthworms are not good composters.
- Organic Kitchen Waste- Do feed with fruit and vegetable scraps, including peels, coffee grounds, tea bags, cereals and crushed eggshells for a source of calcium. Keep citrus to a minimum. Shells left intact, or avocado skins, provide a place where worms will hide together. Do not feed worms with meat scraps or bones which attract ants and rodents. Dairy, oils, onion, garden debris and pet waste should also be avoided.
- Environment- Choose a convenient location out of direct sunlight such as a garage, patio, or basement. Optimal temperature for worm composting is 59F to 77F. Temperatures outside this range will slow the process; extreme temperatures will kill the worms. Maintain adequate moisture and ventilation for best results.
Initial Set Up, Care and Maintenance
- Place moistened bedding in worm bin. Bedding should express a few drops when squeezed in the palm of your hand. Fill bin 80% with bedding.
- Scatter the red wiggler worms on top of the bedding. They do not like light and within minutes will work their way down.
- To feed, distribute small food scraps underneath the bedding, and close the lid. Feed worms every 5-7 days.
- Do not overfeed or the vegetable matter will rot. Remove excess or rotting food.
- At each feeding, check that the bedding is still moist and add new bedding as needed.
- Worms do best when disturbed as little as possible. It is not necessary to provide care daily or to turn the compost.
- Covering the food and bedding with cardboard assists in keeping the bin dark and cool.
- Excess moisture will collect in the bottom of the bin. Remove this worm tea as it accumulates. It is full of nutrients and can be used to fertilize your plants.
- In the summer months, temperatures above 86F will be harmful to the worms. Keep the bin in the shade, bring it indoors, or cover with a damp blanket.
- In the winter months when temperatures drop below 40F, insulate the lid, place bales of straw around it, or bring indoors. At freezing, the worms will die.
- With proper care, worms will actively reproduce.
Harvest
- Harvest worm castings every 2.5 to 6 months depending on the number of worms and how much they consume.
- To harvest, empty the bin contents onto a large sheet and sort through. Return any worms or food to a newly prepared bin. Alternately, you can push the contents of the bin to one side and place fresh bedding and food on the vacated side. Within a few days, the worms will move over to the new food source leaving the vermicompost for you to harvest.
- Vermicompost will not burn your plants. However, do use sparingly as a little goes a long way. It can be used on seed beds, transplants, or simply spread on top of soil.
- Once harvested, start the process again in the empty bin.
References
Applelhof, M. & Olszewski, J. Worms Eat my Garbage, Story Publishing. 2017.
Composting with Worms. OSU Extension. Clackamas County Master Gardeners. Composting with Worms (clackamascountymastergardeners.org)
Composting with Worms. UCCE Master Gardeners of San Joaquin County. Composting with Worms - UCCE Master Gardeners of San Joaquin County (ucanr.edu)
Sousa, Mary. Vermicomposting-Composting with Worms. UC ANR. UCCE Master Gardeners of San Joaquin County. 2015. Vermicomposting - Composting with Worms - What's Growing On - San Joaquin UC Master Gardeners - ANR Blogs (ucanr.edu)