290-Understanding Vermicompost and the Benefits of Worm Castings

| Compost, Podcast

Vermicompost is one of the most effective products created by using worms to recycle organic material, usually waste, to produce an extraordinary soil amendment rich in beneficial microbes. But it took quite a while for vermicompost to catch on as viable means to divert organic waste from household trash bins and landfills. To share the history and benefits of vermicompost and the key facts to know, my guest this week is Rhonda Sherman, the author of “The Worm Farmer’s Handbook” and a world-renowned expert in the field.

This episode is all about what the worms produce — vermicompost. Next week, we will go into the details of how to make vermicompost, through the process of vermicomposting.

Rhonda is an extension specialist and the director of the Compost Learning Lab at North Carolina State University in Raleigh. She travels far and wide to present workshops on vermicomposting and consult with farmers, businesses and institutions on the development and management of vermicomposting systems. She also organizes the annual NC State Vermiculture Conference, which draws participants from around the globe,  


Rhonda Sherman

Rhonda Sherman is an extension specialist and the director of the Compost Learning Lab at North Carolina State University and the author of “The Worm Farmer’s Handbook.” (Photo Courtesy of Rhonda Sherman) (Photo Courtesy of Rhonda Sherman)


North Carolina State University hired Rhonda in 1993 because recycling had just been mandated in the state. North Carolinians, from households to landfill managers, were reaching out to NC State, a land-grant university, asking how they could recycle.  

“I was hired to answer their questions and educate them about recycling, but I was attending state and national conferences on recycling, and everything was cans, paper, bottles — that’s all they talked about,” Rhonda says. “And I thought, wait a minute, what about food waste?”

She pitched seven ideas to publish, and the last in the pile was “Worms Can Recycle Your Garbage,” about household vermicomposting.

“My engineering colleagues scoffed and laughed at me,”  she recalls. “They said, ‘What are you gonna write about worms? Are you crazy?’”

But once published, it was difficult to keep copies of  “Worms Can Recycle Your Garbage” on the shelves.

“There was a frenzy of interest in vermicomposting,” she says. “That totally took me by surprise. I didn’t realize that would happen. So I say I accidentally became world-famous about vermicomposting because it was not my intention.”

She soon held a half-day workshop on large-scale vermicomposting, and there was great interest, so much so that she would later organize a two-day conference. She’s now been putting on the NC State Vermiculture Conference annually for 22 years. In her time sharing the possibilities of vermicomposting, Rhonda has been contacted by people in 122 countries wanting to know more.

Vermicomposting & Food Waste

Food waste is the No. 1 waste going into landfills, and when food waste decomposes in the oxygen-less environment of landfills, it creates methane, a huge contributor to climate change, Rhonda points out. 

“The problem’s here,” she says of climate change. “It’s not in the future, it’s here. So we really need to get serious about it. But it’s so easy to keep food waste out of landfills by either vermicomposting or composting or both in your backyard or in your home.”


Worm bin

In a worm bin, food waste is turned into valuable vermicast while diverting it from a landfill. (Photo Courtesy of Rhonda Sherman)


The Worm Farmer’s Handbook

The Worm Farmer’s Handbook” is such a fun read. If you wanted to be a worm farmer, this is the book to go to. It also educates readers on how amazing the worm is, what it does and its contributions to the composting cycle.

Rhonda published the book four years ago. She says it was fun to write because, for once, she could write in her own voice, as opposed to her university work, when her writing is dry, concise and in the third-person. Rhonda wanted “The Worm Farmer’s Handbook” to be informative as well as fun to read, with lots of color pictures of worm farms around the world. 

One of the worm farmers included in the book is Jack Chambers, of TerraVesco — formerly Sonoma Valley Worm Farm — in California, who you may know from watching my public television program “Growing a Greener World.” Jack appeared in the very first season, and I visited Jack again just last year for season 12. Jack’s company is the maker of TerraThrive, a vermicompost product for improving soil microbiology. (You can purchase TerraThrive with free shipping on orders over $50 at

“The Worm Farmer’s Handbook,” from Chelsea Green Publishing, was first published in 2018.


The Work Farmer's Handbook

“The Work Farmer’s Handbook” by Rhonda Sherman


Not All Earthworms Are Alike

There are more than 9,000 species of earthworms, ranging in size from half an inch to 12 feet long.

“That’s mind-blowing,” Rhonda says. “That kind of changes your idea of ‘Oh, yeah, I know what an earthworm is.”

Scientists have sorted these 9,000 species into three different groups based on where they live and what they eat.

Anecic earthworms are what most people are familiar with. Nightcrawlers are in this group. Anecic earthworms have vertical burrows underground and live in and eat soil. Overnight, they’ll come out and grab some leaf litter and take it back to their burrows.

Endogeic earthworms live underground in horizontal burrows and eat soil. 

Epigeic earthworms don’t live in soil. Rather, they live above ground and eat decomposing organic materials. You’ll find them at the bottom of a leaf pile or cold compost pile or in animal dung, such as cow patties. These are the types of worms used in vermicomposting. There are seven that are ideal for vermicomposting operations, the most notable of which is the red wiggler.

While some people insist that composting worms are not earthworms, Rhonda says they are, in fact, earthworms — even though they don’t live underground. 

It’s important to realize that worm bins should not be filled with dirt, because epigeic earthworms do not live underground and they don’t intentionally consume soil. Epigeic earthworms want food scraps and things like shredded newspaper — not dirt. In fact, tossing red wigglers into your raised garden beds is a mistake. That’s not where they want to be. They likely won’t even survive in a garden in full sun that dries out between waterings.

Epigeic earthworms live in shaded, moist places, under decomposing material. When you find worms in your raised bed gardens, they are anecic or endogeic earthworms, though most likely anecic, Rhonda says.

No earthworms like light, which explains why anecic earthworms only come out in the dark to grab leaf litter. However, earthworms do not respond to the red light frequency, so it’s best to use red light to examine or search for earthworms.



It’s important to recognize that not all species of earthworms thrive in worm farms. Worms that live in soil don’t belong in your worm bins.


Earthworm Facts & Myths

A third of an earthworm’s vital organs are contained in the front third of its body. Once you know that, it’s easy to recognize that it’s a myth that cutting an earthworm in half will yield two worms. 

The light-colored band nearest the front of the earthworm is called the clitellum, and that’s where the worm’s reproductive organs are found. Rhonda noted that supermodel Heidi Klum’s 2022 Halloween costume — she went as an earthworm — was backward. She had the clitellum closest to the tail end of the worm rather than the front. 

Earthworms have tiny mouths and no teeth. They don’t have eyes or ears, but they can sense their way around with their skin and muscles. They can sense light and vibrations and respond. 

They don’t have lungs either. They breathe through their skin, so their skin must stay moist in order for the transfer of gasses to take place.

Another myth about earthworms is that they come up from underground during the rain because they could drown in their burrows. This is not the case. In oxygenated water, earthworms can live for weeks. What’s really happening when it rains is that worms come out of their burrows to seek a partner, food or a new place to live. 

Microbe Factories

Rhonda refers to earthworms as “microbe factories.”

After soil or organic material passes through the digestive tract of an earthworm, it is much more nutrient rich and full of microbiology than when it started.

Earthworms suck in tiny particles the size of coffee grounds, plus microorganisms. And even more microorganisms live inside the worms. What comes out the other end of the worm has many more microbes than what was originally consumed, Rhonda says. “Vermicast is just packed with microbes.”

The NPK ratio (nitrogen-phosphorus-potassium) of vermicast is not consistent. It depends on the worms’ diet. 

“Did you feed them dairy manure? Did you feed them hog manure? Did you feed them food waste? Did you feed them paper waste?” Rhonda says. “It’s all going to have different NPK at the end, and what’s really interesting about vermicast is that NPK is not the star of the show.”

The real star of the show is the organic matter and the cation exchange capacity, or CEC.  Worm castings are high in humic and folic acids and they have a high CEC, which helps soil to better hold nutrients and to release them to plants. 

The variety as well as the sheer volume of microbes in castings outcompete regular compost in contributing to plant growth. And a little bit goes a long way. Compost may cost you $30 to $35 per cubic yard while vermicompost can cost $200 to $1,200 per cubic yard. So it’s great news for gardeners that much less vermicast is needed to have the same effect — or an even greater effect — on soil fertility.

Rhonda emphasizes that there is material other than worm casting that comes out of worm bins. It’s organic material that hasn’t been consumed, and it has different microorganisms and different nutrients that contribute to what makes vermicompost, or vermicast, so great. But it’s not 100% castings, no matter what marketers may say.

“You would have to attach a bag to the end of every worm to end up with that,” Rhonda says of 100 percent castings.


Earthworms in compost

Vermicompost contains more than just 100% worm castings. Unconsumed organic materials is also in the mix. (Photo Courtesy of Rhonda Sherman)


Vermiculture Vs. Vermicomposting

Vermiculture is earthworm breeding, while vermicomposting is producing worm castings. 

Vermiculture requires different feedstocks and rearing techniques, Rhonda says. “The purpose is to create healthy worms that you can sell.”

Worms are raised to sell to worm farms but also for bait or for feeding pets and livestock.

Vermicomposting uses waste materials rather than purchased feedstock and turns that waste into a super-beneficial product.

Rhonda notes in her book that the size and reproductive rates of worms in a vermicomposting system are frequently lower than those in vermiculture systems. This speaks to the difference between the end goals of vermicomposting and vermiculture.

Composting Vs. Vermicomposting

Composting involves microorganisms breaking down organic materials. In hot composting, the microbial activity creates heat. When there is a high volume of materials, that heat gets trapped. The temperature rises from mesophilic temperatures (ambient, moderate temperatures) to thermophilic (hot) temperatures. Under these conditions, mesophilic microbes either die or grow armor and hibernate, and thermophilic microbes become dominant. 

When most of the organic materials feeding the microbes have been consumed, the temperatures drop, and the mesophilic microbes wake up again and help to finish and cure the compost.

To achieve enough volume for hot composting, at a bare minimum the compost pile should be 3 feet by 3 feet, Rhonda says. 

Vermicomposting is a mesophilic process, so you don’t want that kind of volume when practicing vermicomposting. If the pile gets hot, it can kill the worms. Maintaining mesophilic temperatures will lead to a greater variety of microbes. 

In vermicomposting, organic material (food waste, animal manure, leaves, etc.)  is passing through an animal and coming out the other end as organic matter supercharged with beneficial microbes that allow for nutrients to make their way into plants and fight detrimental fungi and bacteria. 

“Vermicompost and compost in some ways might look similar, at a distance,  but they’re very different,” Rhonda says.


Adding vermicompost

A little bit of vermicast goes a long way in improving your garden soil.


Why Vermicompost Is Beneficial to Plant Growth

In the early days of Rhonda’s annual vermiculture conference, the scientists who studied the effects of vermicast on plant growth still had not figured out why the plants had such greater growth.

“They were referring to it as ‘magic,’ and that is not a good word coming out of scientists,” she says.

As the years went by, scientists announced that they had begun to unlock the secrets of vermicompost. They learned how the humic and folic acids in vermicompost affected soil chemistry.

“There’s just so much going on, and I think there are still things that have not been discovered,” Rhonda says.

For those who really want to dig deep on vermicast benefits, she says to look it up on Google Scholar and check out the peer-reviewed studies. “That’s a really easy way for the average person who doesn’t work at a university to be able to access research papers,” she says.

Among the benefits of vermicast that scholarly articles identify are: seeds germinate more quickly, an enhanced rate of seedling growth, increased root numbers in the biomass, improvement in root stress tolerance, earlier flowering of plants and increased plant yields. 

Vermicast has also been found to decrease plant transplant shock and increase plant vitality and flavor profiles. Plants grown with vermicast have more leaves and flowers, more total leaf area, greater plant biomass, and higher leaf chlorophyll content. And that’s not an all-inclusive list.

One study featured in Rhonda’s book was a turnip trial. One turnip plot was grown without any castings, one was grown with 10% castings and another was grown with 20% castings. Each plot had equal amounts of nitrogen, but the turnips grown with 20% castings grew the largest. 

“That’s where you get into the humic and folic acids and the plant growth hormones and the huge diversity of microorganisms that are involved,” Rhonda says. “So it’s really those things that were causing the differences in the size of the turnips. The greens were so much bigger with the addition of vermicompost, and the roots were incredible compared to the control.”



Between 10 and 20% vermicast is the right soil mix for supersized turnips. (Photo Courtesy of Rhonda Sherman)


Though 10% and 20% vermicompost had great returns, a turnip grown in 30% vermicompost, while larger, would not be significantly bigger — so there are diminishing returns. And then when going up to 50% vermicompost, the turnips grow only as large as the control turnips with 0% compost, so clearly too much is too much.

Vermicast, Insects & Pathogens

Vermicast has attributes that combat insect pest issues. 

“By adding vermicompost to the soil, it makes plants resistant to arthropod insects, and it’s because vermicast is rich in phenolic compounds, which are repellent or toxic to many types of insects,” Rhonda explains. “Because the phenolics taste bad and can disrupt insect digestive systems.”

Sucking and chewing insects hate vermicompost. Aphids, caterpillars and two-spotted spider mites on cabbage, mealybugs on eggplants and bush beans, and two-spotted spider mites on tomatoes and cucumbers are all reduced when vermicompost is used. Likewise, nematodes, including root-knot nematodes, are reduced.

Studies also show that vermicompost use reduces plant pathogens. One study looked at pythium rot in cucumbers and found that vermicast knocked the infection rate down practically to zero. 

That same study compared sterilized vermicompost and unsterilized vermicompost. The control group, with no vermicast, was full of pythium, and the sterilized vermicompost barely affected the pythium. But the unsterilized vermicompost, which is rich in beneficial microbes, knocked out the pythium.

When storing or packaging vermicompost, it’s important to take a few precautions. Those beneficial microbes will die in UV light if the vermicompost is left exposed, and they will die if they are in a sealed container with no air. And they need food and moisture too, like all living things.



Lettuce grown in 20%, 15%, 10% and 0% vermicast. Plants grown in vermicast are shown to have fewer pest and disease issues. (Photo Courtesy of Rhonda Sherman)


How to vermicompost at home will be the subject of next week’s episode, so be sure to come back and catch Part II.

I hope you enjoyed my conversation with Rhonda Sherman. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title. 

Have you used vermicompost in your garden? What were the results? Let us know in the comments below.

Links & Resources

Some product links in this guide are affiliate links. See full disclosure below.

Episode 117: Compost, Compost Tea and the Soil Food Web, with Dr. Elaine Ingham

Episode 211: Invasive Asian Jumping Worms: What Gardeners Need to Know

Episode 282: The Vital Role of Soil Bacteria in the Garden, with Jeff Lowenfels

Episode 283: A Soil Chemistry Primer: How Protons and Electrons Influence Soil Moisture and Fertility

joegardenerTV YouTube: How to Make a Functional Worm Bin

joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.

joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course membership opens in 2023. Sign up for the waitlist here.

joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.

joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier. 

joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!

joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.

joegardener Newsletter

joegardener Facebook

joegardener Facebook Group

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joegardener Twitter

joegardenerTV YouTube

Growing a Greener World®  

GGWTV YouTube   

GGW Episode Episode 112: The Power of Worms

GGW Episode 1213:  Sonoma Valley Worm Farm: Where Are They Now?

The Worm Farmer’s Handbook: Mid- to Large-Scale Vermicomposting for Farms, Businesses, Municipalities, Schools, and Institutions” by Rhonda Sherman

Vermiculture Technology: Earthworms, Organic Wastes, and Environmental Management” edited by Clive A. Edwards, Norman Q. Arancon and Rhonda Sherman

Tea Time in the Tropics” by Norman Arancon and Theodore Radovich (free PDF)

NC State Extension Composting Guide

NC State Extension: Worms Can Recycle Your Garbage 

NC State Extension: Vermicomposting for Household

NC State’s Vermiculture, Composting & Recycling Program on Facebook

Homegrown YouTube: Worms Can Recycle Your Garbage (Vermicomposting)


TerraThrive — Free shipping of TerraThrive on orders over $50

Greenhouse Megastore – Our podcast episode sponsor and Brand Partner of – Enter code JOEGARDENER for 15% off your order

Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, AeroGarden, Milorganite, Soil3, Greenhouse Megastore, PittMoss, Territorial Seed Company, Earth’s Ally, National Wildlife Federation and TerraThrive. These companies are either Brand Partners of and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

One Response to “290-Understanding Vermicompost and the Benefits of Worm Castings”

  • Julie Tengel says:

    Wow, thanks for interviewing a vermiculture specialist. I have been wondering for a long time what the difference is between worms and now I now. I have seen a few times that people say it okay to add vermiculture worms to compost. Now I know its not true. LOve it

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