What is “vermicompost”?

Composting is a great way to help the environment. Composting reduces the amount of waste sent to landfills. It also produces a great amendment to your garden soil.

There are two main types of home composting: thermophilic composting and vermicomposting. Traditionally, composting refers to thermophilic composting, which is merely composting using the natural heat produced during the process…read on to learn more!

vegetable scraps on compost pile
Vegetables, paper towels, and yard waste can be thrown into a backyard container for composting. Credit: M. Pings

Both types of composting take organic matter–whether vegetable waste, compostable paper products, or yard waste–and decompose it. Even your coffee grounds and paper filters are great components for compost. Did you know you can compost the cardboard centers of paper towels and toilet paper rolls?

Composting takes this waste and turns it into nutrients we can return to the soil. While thermophilic composting and vermicomposting both break down our unused plant-based waste, they are quite different processes. Luckily, we all can make our own personal compost systems at home.

Thermophilic composting is the traditional composting method. No matter what size your composting bin is, it takes heat to break down the organic matter. Where does this heat come from? The chemical and biological processes of the microbes themselves create heat! Of course, in the summer months compost piles can pick up atmospheric heat, too.

Temperature is an important part of thermophilic composting (the name itself means heat loving!). A key component of this type of composting is a warming-up and plateau of temperature around 50°C (about 120°F) for a period that lasts for weeks to months. During this hot period, microbes that excel at breaking down tough materials proliferate. This stage of composting also succeeds in killing many pathogens that may have initially been present in the material. To ensure retention of heat necessary to foster the heat-loving microbes, a compost pile must be large, generally of a volume greater than 15 gallons.

Some traditional composters make “messy” piles in the back of their yard. Others enclose their compost in bins. All thermophilic compost piles must have some part of the pile connected to the ground–either through holes or just being placed on top of bare soil. This allows earthworms, insects, and those important soil microbes to get in and do their work.

Turning over the material in thermophilic compost piles is important. This ensures that the pile does not become too hot (more than 65°C, or 149°F) for the microbes, and supplies oxygen to the microorganisms. This high oxygen environment ensures efficient decomposition of the original plant matter so the compost is ready to use faster. Once the heat-loving microbes have worked through the material, the pile will begin to cool as the decomposition process slows. At this point, normally after 2-4 months, the compost is considered mature and ready to be used in your garden. Thermophilic compost is rich in stable organic matter that will provide important water-holding capacity.  Compost also provides more structure to sandy soils.

Vermicompost uses worms to mix and process organic waste products into compost. This results in compost faster than traditional methods. Piles can be smaller, and there is no need to turn the piles. A vermicompost system uses certain worms, typically red wrigglers, that like to live in organic-rich soils. These worms are placed in a modified tub with organic waste (see here https://www.epa.gov/recycle/how-create-and-maintain-indoor-worm-composting-bin for more details and an easy DIY). The worms eat the materials in the bin and create casts. Casts are the nutrient-rich by-products of the worms’ digestive process. These casts are the vermicompost that can be applied to soil. Vermicompost provides the same soil benefits as thermophilic compost. It often has a slightly higher nutrient content and availability than thermophilic compost.

One of the main benefits of vermicompost is that there is no amount of waste too small to get started. This makes vermicomposting especially attractive to apartment-dwellers who may not produce quite as much compostable waste as those with yards. Additionally, vermicomposting is much faster than thermophilic composting in producing a soil-ready amendment (about a month versus 2-6 months).

However, there are some potential environmental concerns with vermicomposting that should be considered when deciding between the two methods. One is that the various types of worms used for vermicomposting are not native to the United States. They can be potentially destructive to our ecosystems. If allowed to get into the wild, these non-native worms remove the thick layer of decomposing leaves under trees in forests of the Northeast and Midwest. And, as with non-native plants and insects, vermicomposting worms can easily outcompete their native earthworm cousins. For this reason, caution should be taken with the use of vermicompost material.

Mac Callaham, a research ecologist with the USDA Forest Service (and native earthworm lover), suggests that vermicompost be microwaved for three minutes prior to garden application.1 The resulting heat will kill any lingering worms and their eggs, while still retaining the beneficial nutritional and structural qualities of compost. He also suggests using earthworms from your yard or a local forest for your vermicomposter. They may not be natives, but at least new species won’t be introduced.

Another concern is there is no warming stage for vermicompost, so potential pathogens to humans and plants may persist. Depending on the initial organic waste, and how you want to use your compost, this may be an important consideration.

There are key differences between thermophilic composting and vermicomposting that may make one more appealing to you. As a current apartment-dweller, I have a small vermicompost system! Whichever method you chose, both thermophilic compost and vermicompost are great ways to reduce your waste output and create a great soil-improving amendment. Contact your local extension office for specific recommendations about composting in your region, as soils vary from state to state, county to county–and even yard to yard!

Answered by Caitlin Hodges, Pennsylvania State University

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1. Callaham, M. A.  2016. Earthworms in composting: are the rewards worth the risks? Athens Master Composters. Athens, GA.

See the links below for more detailed information about proper care and keeping of compost and to learn more about invasive earthworms:

https://www.epa.gov/sustainable-management-food/types-composting-and-understanding-process

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