What types of food stuffs should not be put in the worm bin?

“What types of kitchen food stuffs should not be put in the worm bin?” ~ Mike

Good question Mike,

There is a lot of ‘gray area’ when it comes to what can and cannot be added to a vermicomposting system. Really, I would say it depends on your experience level and what exactly you are trying to accomplish. The size and location of your system are also very important considerations.

When just starting out, I highly recommend taking a fairly cautious approach – moderation is the key, and it is better to stick with those materials widely recommended for worm bins.

Fruit and vegetable scraps are always a safe bet – they are pretty well the best kitchen wastes for your bin.

It is ideal to cut them up and let them ‘age’ for a little while before adding them to the bin, but this is certainly not critical for success. Aging allows time for microbial colonization and the start of the decay process.

This can be done in the worm bin itself, but the worms generally won’t start feeding on the materials until they are starting to rot (since the microbial ‘soup’ is what provides much of their nutrition).

It’s also a good idea to mix a little bedding (shredded cardboard, peat moss etc) in the fruit/veg scraps when you add them since they are very water-rich, and the bedding will help soak up some of that excess moisture. Tea bags and coffee grounds are also great additions to your worm bin, but tend to be fairly acidic so you won’t want to go overboard with them.

Starchy materials such as rice, pasta, potatoes, bread etc can be somewhat troublesome for new vermicomposters because they can get moldy quite quickly and if decent amounts are added at once they can also go ‘anaerobic’ (no oxygen) and start fermenting. I can still vividly remember back to a time when I dumped a big clump of cooked rice in my worm bin (my first bin, I might add!).

Not only did it create a stinky mess, but it also resulted in a major population of white worms (which can spring up when conditions become sour in your bin). As part of a school worm composting project I tested rice and other starchy materials, such as donuts, in the bins and ended up killing quite a few worms and again creating a stinky mess yet again.

Don’t get me wrong, starchy materials are totally fine if you know what you are doing – especially if you have a nice big system and spread the materials out. I wouldn’t give a second thought to tossing rice or pasta in my big outdoor worm bin, that’s for sure.

Strongly acidic materials, such as citrus waste and pineapple should be used in moderation as well. Worms are very tolerant of low pH, but you don’t want to quickly throw off the balance of the ecosystem in the bin by adding too much acidic waste. Again, the size and type of system you are using can make a huge difference.

I’ve added a LOT of orange peels and rotten oranges at once to my outdoor bin without any trouble whatsoever. Would I do the same with one of my indoor plastic bins?

Not likely (but will still add moderate amounts of citrus waste).

Aside from the acidity of citrus fruit, the peels contain a potent oil than irritate the worms’ skin. Same is true of hot peppers and onions, so again use a little restraint with these as well.

Oils and oily foods generally should be avoided. They are slow to break down and the oils can coat the worms’ skin making respiration difficult (worms breath through their skin). A little leftover caesar salad or some fried green tomatoes etc won’t generally cause too many issues, but just be a little more cautious.

Meats and dairy shouldn’t be added to a worm bin – processed meats and cheese often contain lots of fat and salt, among other things that can potentially irritate your worms. They also tend to petrify fairly quickly, causing nasty odors and releasing potentially harmful gases. Outdoors in a larger system you could compost these, but they need to be buried well so as not to attract the attention of local scavengers.

Highly resistant or non-biodegradable materials shouldn’t be added to a worm bin because they won’t get processed. Corn cobs, fruit pits, and woody wastes can all be added (worms actually seem to like making a home out of corn cobs), but they will take a LONG time to fully break down.

Anyway, Mike – I think that pretty well covers the basics as far as kitchen wastes go.

Hope this has helped.

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