Worm Bedding & Castings

“I love your newsletter. Thanks for taking the time to send it out so often! My question is this: I just started my first worm bin a couple of months ago. Will all of the bedding disappear and turn into castings in time, or will I have to separate the castings from the bedding at a certain point?

How do I know when to add more bedding? I am eager to harvest my castings… how long will that take? (My bin is about 2 feet x 1 foot with 500 worms that are happily multiplying.)Thanks!” ~ Andrea

Hi Andrea,

In time, all ‘bedding’ material will indeed be converted into worm castings (or at least ‘vermicompost’, which is basically a mix of castings with composted materials that have not passed through a worm’s digestive system).

As long as you continue to add new bedding however, you will continue to postpone the conversion of ALL of the worm bin material into compost – i.e.. you would have to stop adding new food and bedding and let the system sit for a month or two in order to achieve a uniform material.

Since adding new bedding/food is an important part of vermicomposting (more on that in a minute), you will in fact generally need to do some separation of unfinished from finished materials.

Ideally, this will be done using some sort of screening system since it will make the process a lot easier. But let’s face it – most regular-joe (and joette) vermicomposters won’t have their own ‘screening system’, so a more basic approach will likely be a more realistic option.

One very simple technique when using a regular worm bin is the “dump and sort” approach, also known as the “light harvesting method”. As the names imply, you simply dump out the contents of your bin (preferably on a tarp), and take advantage of the fact that worms hate light by slowly brushing the dark composted material (usually at the top since it was from the bottom of your bin) off to the side.

The worms will continue diving down, and eventually you will be left with a bunch of worms in partially-processed bedding etc, which can then be added to a new system – preferably one that has been set up with food and bedding a number of days beforehand.

When using plastic worm bins (those with an enclosed bottom, that is), this process can be a bit of a chore since the material tends to be quite wet. You may need to leave your heap to sit for a couple days in order for it to dry out sufficiently. This is best accomplished outdoors during dry summer weather, but a dry basement will work (albeit more slowly) as well.

Back to your question about how often to add bedding. I personally recommend adding new bedding pretty well every time you add wet food waste to your bin – especially important when using a sealed plastic system, since there is a tendency for water to pool in the bottom. This may not be necessary when you first set up the bin since there will be lots of new bedding in there, but it’s not a bad idea to get into the habit of adding a little bit with each feeding early on.

I should ALSO mention that one excellent way to avoid the hassles I mentioned above is to use a “flow-through” system, something we’ll chat more about next week. 🙂

Hope this helps!

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