Worm Castings vs Vermicompost – Whats The Diff?

I tend to use the terms ‘worm castings’ and ‘vermicompost’ interchangeably here on the site, when technically speaking they are not quite the same thing.

Worm castings are literally little worm turds (for lack of a better word – haha) – that is to say, material that has gone in one end of the worm and out the other. If you have 100% pure worm castings (virtually impossible to achieve) you should have a material that looks a lot like coffee grounds.

Vermicompost is really a more accurate term when it comes to the material produced in most worm composting systems. It is basically a mixture of worm castings, partially composted wastes, and any resistant materials that won’t readily break down. Really high quality vermicompost should have a high percentage of worm castings in it, but the chances of having every last bit of material in your system pass through a worm at least once is pretty slim.

I’ve talked previously about the awesome vermicompost produced by Worm Power. Although I referred to it as ‘worm castings’, it isn’t 100% pure castings, but there is definitely a very high percentage. If I remember correctly, they actually let the material pass through the flow-through system twice in order to ensure that it is as close to pure castings as possible!

The problem is that there are no standards in place to dictate what percentage of worm castings has to be present in order for a product to be “100% pure” – nor are there really any ways to accurately measure the castings percentage. It really just comes down to the look and feel of the material, the reputation of the company producing it, and of course its ability to boost plant growth.

Anyway – definitely not trying to split hairs here – just thought some of you might be curious about the technical difference between these two terms!

[tags]worm castings, worm compost, vermicompost, vermicast, compost, worm composting, vermicomposting, worm power[/tags]

**For Even More Worm Fun, Sign Up for the RWC E-mail List!**
Previous Post

Sour Worm Bin Saga Continues

Next Post

Lethargic Worms & Worm Tea


  1. Bentley – great article. It is definitely a topic worth discussing (as it comes up all the time). From a product liability standpoint – it’s very difficult to call anything 100% nowadays without some level of worry or misrepresentation (as it should). In my mind, premium vermicompost should contain a large percentage of castings – combined with the undigested portions of the composted (quality controlled compost) material that the worms thrived in (i.e. from the same system). The goal should be to produce a material that contains beneficial biological, chemical and structural properties (the building blocks of great soil). Some level of diversity in the finished material (such as that in vermicompost) would be required to meet these three (3) criteria. Also – regarding the lack of standards, you hit the nail on the head. This plagues the industry from hitting that credibility mark. What needs to continue is real scientific testing (like that happening at Cornell University and others) to determine what mechanisms or combination of mechanisms make vermicompost / worm casting material work as great as they do.

    • Bentley
    • April 25, 2008

    Heya, Shawn! Thanks for popping by a sharing your thoughts. Great info!
    You are definitely right about the need for more scientific testing as well. Hopefully, as the use of vermicompost becomes more popular, we’ll see an increase in the number of researchers taking an interest in it.

  2. Hello, my name is Shannon and I represent a vermicomposting facility in Stony Plain, Alberta, Canada. Are you aware of any data that describes what the typical makeup of vermi cast/vermi compost is in a flow through reactor and what some of the methods are to increase the percentage of casting in a reactor?

    • Bentley
    • October 8, 2019

    Hey Shannon – sorry for the delay! Just saw your comment now. Data concerning the make-up of castings is a very complex topic unfortunately. I recommend doing some searches in Google Scholar – you should be able to find research summaries that can help answer some of your questions about this. As for increasing the percentage of castings – retention time is important, type of wastes and how well optimized they are (eg broken down into smaller particles can help the microbes and worms a lot, meaning more of it will likely end up passing through the digestive tract). The quantity of resistant materials in your food is also an important factor – really resistant materials will likely never end up as castings, so if you have lots of this in your mix it will be more challenging. Bottom line, I wouldn’t obsess about it – top notch vermicompost should be your goal – not the unrealistic goal of “100% castings”. Hope this helps!

Leave a Reply

Your email address will not be published.

Get Your Free Vermicomposting Guide!

* Join the Red Worm Composting E-Mail List Today *