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Top stories of 2023: Worm is the word

Could vermicomposting manure work on a commercial scale?

December 19, 2023  by James Careless

Vermicompost from pre-composted dairy manure after 70 days. All images courtesy of Black Diamond Vermicomposting

Never underestimate the manure management power of earthworms. That’s the lesson inherent in vermicomposting, the natural process by which earthworms consume manure and then excrete an ecologically benign natural fertilizer known as “worm castings.” (A more accurate term might be “worm manure”.)

“Vermicomposting is a degradation and stabilization of organic wastes by earthworms and microorganisms into soil amendments that are rich in plant nutrient elements, high water holding capacity and contain plant growth regulators,” says Dr. Norman Q. Arancon, of the University of Hawaii at Hilo. 

The usefulness of vermicomposting for consuming manure has been explored in Manure Manager magazine previously (‘Digging into vermiculture” by Alex Bernard: However, the question that matters most to manure managers is whether or not this approach can be used for large-scale manure conversion. Here is what we have found.

Vermicomposting revisited: A quick primer
Vermicomposting is a natural aerobic process which differs from traditional composting. Earthworm casts are a ready-to-use fertilizer that can be used at a higher rate of application than compost, with nutrients released at rates growing plants prefer. In terms of the actual amount that can be added, “general industry knowledge is anything more than 20 percent by volume can be detrimental, depending on the plant and soil,” says Cristy Christie, owner of Black Diamond VermiCompost in California


Better yet, it only takes earthworms 22 to 32 days to convert organic wastes into casts, depending on the density of the waste and how mature/large the earthworms are. Once the casts are ready, they require two weeks for their natural ammonium to convert into nitrate, a substance that plants can use.

In contrast, regular composting requires 30 to 40 days, followed by three to four months ‘curing’. This last phase is required because compost generates a lot of heat during its first stage, which kills off some beneficial bacteria and motivates earthworms to leave. Curing allows this process to reverse.

Speaking of vermicomposting manure systems – which do not heat up quite significantly – the rule of thumb is to mound them no more than two inches high and eight wide “because you need to stand on both sides of that pile and be able to look into the middle of it,” says Rhonda Sherman, a retired extension specialist formerly with the department of horticultural science at North Carolina State University. “You need to put your eyes on all parts of the pile, so that you can check the conditions for the earthworms.”

“Worms should not be crowded, so the ideal stocking density is 150 earthworms/L of wastes,” recommended “Earthworms ingest about 75 percent of their body weight/day; a 0.2 g worm eats about 0.15 g/day. If you discover earthworms trying to escape any system, it is a good indication that something is wrong with their feed or environment.” (Note: Christie says the actual percentage is “more like 25 percent”). 

As for the right mix for vermicomposting rows? “Cow dung is added with water and mixed well to allow the gasses to evaporate,” says Dr. Venkatesh Devanur, managing director of Som Phytopharma (India) Ltd. At his company, they “dry the slurry to 40 percent moisture. Spread the dung to one metre width, 10 metres length and 0.5 metre height, and spread earthworms on top of the bed.”

“When we look at the effect of the worm compost on the yield, we didn’t see much,” says Dr. Medhi Sharifi, research scientist at the Summerland (BC) Research and Development Center. “But when we look at yield quality, which is very important in wine making, then we see some positive effects. We also noticed that the size of each cluster in the grapes increases when we apply vermicompost.”

“Some observations we have received from growers was the reduction in powdery mildew where vermicompost is used,” he adds. “Powdery mildew is a major fungal disease in grapes, and it causes significant damage yearly to production. The observations that we collected was that when we applied the vermicompost spray, the need for spraying powdery mildew afterwards was significantly reduced.”

Using vermicomposting for large operations
Having established that vermicomposting is a good way to convert manure into an odourless, efficient fertilizer, the next question is whether or not vermicomposting be used on medium- and large-sized cattle farms?

“The vermicomposting system is practical for farm operations since a farm is a good source of organic wastes,” says Arancon. “There are vermicomposting operational units that can even be set up on a household level, so a medium-sized livestock farmer should be able to set up this a system suitable for his scale.”

The same is true for the largest cattle and dairy farms; the only variable is space. Now a large-scale vermicomposting operation “is going to take up more room than your typical mechanical separation system,” said Rick Naerebout, CEO of the Idaho Dairymen’s Association, “so you’re going to have to have the space to do it. But part of what we really like about vermicomposting is the fact that it’s scalable. So depending on the number of cattle you have and the effluent you have to treat, you can scale it to fit your facility: just increase or decrease the number and size of the worm beds you have to fit. After that, vermicomposting is a fairly straightforward technology. It doesn’t take somebody with an advanced degree to know how to run it.”

To set up a vermicomposting operation, one needs to set up a system in “which processed manure are set up in windrows on a relatively flat surface, inoculated with earthworm and after a period of time, processed manure are harvested by separating the earthworms from manure,” Dr. Arancon said. “A more automated system would be based on a continuous flow reactor that allows automation of the process. This will consist of a container equipped with a screen at the bottom to allow harvesting of processed manure at this portion of the system while continuously feeding earthworm at the top portion of the set up. This setup will naturally separate the earthworms from the processed wastes since earthworms will be continuously fed on top leaving the bottom portion of the system processed and then harvested.”

According to the experts, farmers can build their own vermicomposting systems, or hire third-party experts to do the work. One good source for mastering this topic is Sherman’s book, The Worm Farmer’s Handbook, which is available at And the output of such systems can be impressive, whether for use on one’s own farm or for sale to other farms and the public. “Even a farm with just 10 cows can get 50-75 kg of dung per day that can give 20-25 kg of vermicompost a day,” says Devanur.

This said, “a large farm would likely need an expert in worms on staff,” says Christie. “Worms are livestock too, so the same level of knowledge is required for them as it is for cows, horses
or pigs.” •


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