Vermicompost, or worm compost, is the final product of the breakdown of organic material by worms. At Growing Power, we use worms to create a nutrient-rich, organic fertilizer and soil conditioner that we use on all of our growing beds and as a value-added product that we sell at our store and at farmers’ markets.

There are many varieties of worms, but for worm bin composting, we use a few specific earthworm species called Red Wigglers (Eisenia foetida) or Red Earthworms (Lumbricus rubellus). Red worms are often found in soils rich with organic materials in Europe and North America. These species prefer living in compost piles and crawl horizontally throughout the pile to consume rotting food waste. Together with bacteria, red earthworms are the major catalyst for decomposition in a healthy vermicomposting system.

At Growing Power, we utilize two methods for raising red worms and for vermicomposting. The first method is a raised bed or worm bin system. In these bins, we layer red worms and partially decomposed compost. Typically it takes our worms 12-weeks to process the partially decomposed compost into nutrient-rich worm castings. Each of our bins is checked daily to ensure that food waste is still available to the worms and that each bin is moist. At the end of the 12-week time period, we place a screen over the top of the bin and feed the worms new compost. Because red worms are surface dwellers, they will migrate through the screen to consume the new compost. Using this method, we recover approximately 80 percent of the worms from the worm castings. These worms are then used to create the next worm bin.

Our second method for vermicomposting is the use of a static pile called a windrow. Windrows consists of bedding materials for the earthworms to live in and acts as a large bin without walls. Although the windrow has no physical barriers to prevent worms from escaping, the worms stay put because there is a plethora of food for them to feast on.

Vermicompost has a higher nutrient ratio than any other composting method. Additionally, worm castings are also rich with microbial life which aids in breaking down nutrients already in the soil into a form that plant roots can absorb. Worm castings also contain worm mucus which helps soil hold moisture better and keeps nutrients from washing away with the first watering. The following are some of the benefits of vermicomposting:

  • improving soil’s physical structure;
  • improving water holding capacity;
  • enriching soil in micro-organisms, adding plant hormones such as auxins and gibberellic acid, and adding enzymes such as phosphatase and cellulase;
  • attracting deep-burrowing earthworms already present in the soil;
  • enhancing germination, plant growth, and crop yield; and
  • improving root growth and structure.

Vermicompost can be used to make compost or worm tea, by mixing some vermicompost in water and steeping for a number of hours or days. The resulting liquid is used as a fertilizer. The dark brown waste liquid that drains into the bottom of some vermicomposting systems, as water-rich foods break down, is also excellent as fertilizer.

Interested in learning more?
Come to Milwaukee and learn how to build your own system at a Growing Power workshop.