The Science of Worm Castings

Definition of vermicompost

Update to this article - January 2023. I have recently decided to use the term "worm castings" much more frequently than in the past because when searches are done on the internet the key words "worm castings" are used up to 90,000 times more a month than "vermicompost". So, if you've noticed the change, that is the explaination.

Vermicompost is made from the interaction of earthworms and microorganisms breaking down organic matter. As the organic material passes through the earthworm's digestive system it becomes fragmented making more surface area available and also becoming mixed with the worm's incredible intestinal juices and microflora. As a result large amounts of diverse and beneficial microorganisms, low levels of plant available macro and micronutrients, plant growth hormones, humic acids and enzymes are created.
Devine Gardens flowers in grape vine container grown in worm castings

Compost compared to vermicompost

Compost first goes through an active thermophilic stage where the temperature is preferably between 131 degrees or greater. Then it goes through a maturing stage at lower mesophilic temperatures (under 110 degrees). Composting is a good way to stabilize great amounts of waste. Its quality is determined by its feedstock and how it was managed with regards to aerating, moisture, temperature and amount of time in both stages. Compost improves the physical structure of soil, supplies organic matter, adds beneficial microorganisms, buffers pH, stabilizes soluble nutrients and helps plants use them better and can encourage growth. Research has shown that compost helps suppress diseases and pests.
Vermicompost also has two stages. The first is an active stage involving earthworms and microorganisms at a mesophilic temperature preferrably between 59 degrees and 77 degrees. The earthworms mix and fragment the waste providing more surface area for microorganisms. When the earthworms have worked through the waste they move to an area with more food. Then the second stage occurs where the microorganisms finish stabilizing the waste.  Vermicompost generally stabilizes smaller amounts of waste. The quality again is determined by management of moisture, feedstock, temperature, aeration and also a good concentration of earthworms. Because of the intrinsic value that the earthworms bring to the dynamics of the process, vermicompost has the above characteristics of compost but to a higher degree. Vermicompost also brings about additional qualities that make them superior organic amendments as explained below.
Devine Gardens sliced tomatoes grown in worm castings

The effects of vermicompost

Growth & development of plants: Positive results on growth and development of plants include greater economic yields, faster germination rates, earlier flowering, larger yieds, better quality crops, greater leaf areas, higher plant weights, increased root lengths, better establishment of cuttings and higher vitamin content of plant. One reason is that the huge and diverse amount of microorganisms in vermicompost slowly break down organic matter and make more nutrients available for plants to use.
Another reason is a little complicated. Microorganisms produce plant growth hormones (PGH). Since vermicompost has a great amount of microorganisms it therefore contains a lot of PGH but because they are soluble and break down quickly they tend to be ineffective. Vermicomposts also have large amount of humates known to produce positive plant growth. Humates are slowly released to plants.  In a detailed structural analysis of vermicompost the PGH auxin was identified attached to humic acids. (Canellas,L. P., Olivares, F. L., Okorokova, A. L., and Facanha, A. R. 2000. Humic acids isolated from earthworm compost ehance root elongation, lateral root emergence, and plasma H+ -ATPase activity in maize roots. Plant Physiol. 130: 1951-1957). If the PGH in vermicompost are attaching or being absorbed by the humates then the PGH would no longer be soluble and have little effect. They would slow release along with the humates. This could be the major reason why vermicompost helps plants grow so well. Very interesting!
Devine Gardens radishes grown with and without worm castings
 Disease suppression: The ability of vermicompost to aid plants in disease suppression has been studied with many positive results. Possible reasons could be the large biological diversity of microorganisms, antagonistic microorganisms produced from the vermicompost, the plants are stronger because of more pathogen suppressive properties from the vermicompost and SAR (system acquired resistance).
Zucchini squash blossom with cucumber beetles grown in Devine Gardens worm castings
Pest Suppression: Research has looked into what pests ae affected by vermicompost and possible reasons why. white caterpillar, mealybug, two-spotted spider mite, aphids, cucumer beetles, and tomato hornworms are some of the pests that were found to be significantly reduced by the use vermicopost and vermicompost tea. One reason is the plants were healthier so they suffered less dmage from pests. Another reason is the phenolic compounds found vermicompost are distateful the the pests. 

The effects of vermicompost have been studied on tomatos, cucumbers, peppers, peas, lettuce, cabbages, radishes, mushrooms, onions, corn, oats, wheat, tobacco, soybean, peanut, chicory and ryegrass, chrysanthemums, petunias, marigolds, corn flowers, begonias, coleus, raspberries, strawberries, grapes, cloves and black peppers and others. The plant growth medium used for comparisons has included mixes of sand, peat, commercial greenhouse medias and field soils. I hope that you will try using Devine Gardens vermicompost on your plants and you have good results too.
Tina holding cabbages grown with and without Devine Gardens worm castings

What is the difference between castings and vermicompost?

Once, I was asked what I cut my vermicompost with. I was caught off guard and said I don't mix my vermicompost with anything. But because some products are labeled as castings or vermicastings I can see how people would wonder why I label my product vermicompost and doesn't that make my product inferior. So, I have done some research from 2 of my favorite books (listed below) to explain the differences.

Technically, vermi-casts or earthworm castings are only the organic material that has passed throught the earthworm's digestive system and been excreted.

The terms vermi-cast and earthworm castings are often used to distinguish it from conventional compost. Also, in some states there are strict regulations on organic waste hauling operations. Since vermiculture and associated activities are considered an agricultural activity using the terms vermi-cast or earthworm castings can help to point out the difference in the way it was made.

In some finished vermicomposts it may be difficult or impossible to distinguish actual earthworm castings from associated organic materials (including humus) that may not have passed throught the gut of an earthworm but nonetheless have undergone physical and biochemical transformations during the vermicomposting process characteristic of advanced stabilization and humification.

In the book, Vermiculture Technology, it is suggested that the terms vermicompost, earthworm castings or vermicastings may be used interchangeably when strict, process based standards are followed to the processes leading to the accelerated stabilization and humification of organic materials at mesophilic temperatures and under aerobic conditions by ingestion, fragmentation and mixing by earthworms and microorganisms.

Some process based standards should include:
  • Mass of earthworms present in the processing material be at least 1 pound of
    earthworms for each 1/2 pound of food given per day
  • Temperature well below 113 degrees (would indicate thermophilic composting taking place)
  • Monitor moisture
  • Processing time
  • Time allowed to cure
  • How stored
  • Duration of storage
  • Vermicompost system used
  • Raw materials used
  • Preprocessing such as precomposting
  • Any amendments added
The product I sell is vermicompost, which is technically what it is. When deciding on which product to buy the important thing is how it was made. My vermicompost is made with precomposted manure and bedding from our farm animals. After it's precomposted to at least 131 degrees for at least 3 days to kill weed seeds and pathogens it is fed to the worms in amounts that they will eat over the next few days. The worms live in 4' x 8' beds inside, watered frequently and kept warm in the winter with heat cables that do not use a lot of electricity. After the vermicompost is screened to 1/8" before being packaged, becoming "worm castings"

I hope this information helps you make more informed decisions on which brand of vermicompost to buy.