what are worm castings

What are worm castings?

worm castings

If you are new to vermicomposting, one of the first terms you’ll need to know about is “worm castings”. Simply put, the term means worm poop. As worms digest food, the food passes through their body, is broken down into bioavailable forms, and is then passed out as worm castings. If you have a worm bin, you’ll see plenty of worm castings. These are small and pellet-like and look like dark soil.

Let’s talk a little more in detail about what worm castings are.

More about worm castings

The process of using worms to create compost from organic waste matter is known as ‘vermicomposting’. This is similar to composting, with a few key differences. For one, instead of piling up your organic waste in a compost bin, you put it in a little worm bin which you’ve populated with earthworms.

Unlike composting, where environmental factors, fungi and other wildlife break down the waste material, in vermicomposting this task is undertaken exclusively by your earthworms, and worm castings are the end result.

The terms worm castings and vermicompost are often used interchangeably. This wonderful substance contains water-soluble nutrients, and can be used to condition and enrich poor soil. One powerful advantage of using organic fertilizer such as vermicompost is that it enriches your soil in the long-term without getting your plants ‘addicted’ to the extra boost.

 Are worm castings better than compost?


If compost is black gold, your worm bin is a veritable treasure chest!

The consensus seems to be that while compost has higher NPK values (i.e., Nitrogen, Phosphorus and Potassium), vermicompost, when added to the soil, helps aid germination, growth and yield and may overall be better than compost.

In addition, worm castings have been found to be much better than commercially available plant mediums such as potting mixes. This includes growing mediums with nutrients added to them.

There’s also the fact that you have more control over what goes into a worm bin, since it’s on a smaller scale. Bits of plastic and heavy elements (e.g., from colored newspaper pages) are often found in compost heaps.

Do worm castings have a bad smell?

No! When the worm bin is closed, you should notice no discernible smell. When the bin is open, you may notice a mild, earthy smell like that of petrichor or compost. It is a rather pleasant smell, and while it isn’t something we’d perfume our homes with, it certainly isn’t going to be problematic. So, you can place your worm bin anywhere in your home without worrying about it stinking up the place.

In one situation you may notice a strange smell – that is if too much food has been added to the bin, or if the food is too wet. In this case the decomposition becomes anaerobic, and the bin may start to smell of ammonia. (You can usually just add some dry bedding like shredded paper or carboard on top to absorb some of the liquid and also to create a barrier and trap any unwanted smells.)

So to sum up, worm castings are worm poop, and they make excellent organic fertilizer!

worm bucket composter

You can easily make vermicompost with the Worm Bucket Composter, and use the castings in your garden, or to fertilize your indoor plants and herbs. To learn more about vermicomposting – how and why to use worm castings, all about worm tea, and tricks and tips – stay tuned!