Citrus, Paper, Castings

Gary has several really good questions.

Hi Bentley,

I’m a huge fan of your blog – it’s helped me understand worm
composting a lot.

I still have a few questions that I was hoping you could help me out

1) I go through a lot of citrus each week, and probably have over 5
pounds of citrus peel waste each week. I realize for a small
composting system (right now I have just 1lb of worms) that’s probably
too much to just throw in there without upsetting the balance.
However, if I put all the citrus waste in a Bokashi bucket to ferment
first and then added it, would it be okay? Is there another item that
I should add with citrus to help maintain balance, or should I just
try to keep the citrus to a minimum when adding scraps to my bin?

2) I’ve seen some places online claim that you can use your worms to
compost your office paper and junk mail, and I’ve seen other places
say that the ink on those will harm your worms. Is it safe for me to
be adding shredded paper from my home office or am I risking harming
my worms?

3) When making potting soil with worm castings, what else do you use
(I’ve heard coconut coir) in the mix? And what ratio do you mix the
two together? (I’m trying to grow wheatgrass, if that helps.)

Sorry for asking so many questions, but you seemed like the guy to

Thank you,


Hi Gary,

1) Yeah, 5 lbs of citrus is definitely a fair bit, and you are right – probably too much for a standard indoor worm bin. Putting it in a bokashi first might help – definitely worth testing out. Since it is the peels we are talking about, I’m not really sure what to suggest as far as something to mix with it, apart from the usual recommendation of shredded cardboard. I don’t know of anything that will help to balance or neutralize the potent oils in the peels. My recommendation is to start on a small scale and see what happens. If it looks like the peels are breaking down in the bin fairly quickly then you can add more. You may find that you are able to increase the quantity added over time.

2) Worms will indeed compost pretty much any sort of paper product. I personally don’t like using a lot of the white office paper. I suspect that the bleach used to make it white can irritate the worms – I remember setting up a bin using only shredded computer paper and the worms seems pretty keen to leave. In small to moderate amounts, or if using unbleached paper you should be totally fine (I still add some white paper to my bins). I stay away from glossy coloured paper (glossy paper in general, really) – I’ve read that there are heavy metals in some of the inks used. While these won’t necessarily harm your worms, they tend to accumulate in their tissues, and thus in your bin in general over time. I’m a little more easy going about the flat finish colour stuff, but still prefer black and white. I have read that black ink generally isn’t something to worry about. I like newsprint types of paper – like that used for newspapers (obviously), phone books etc. It seems to hold water well and gets consumed quite readily. I also love corrugated cardboard and the pulp cardboard used to make egg cartons and drink holder trays.

3) I generally don’t mix up my own potting soil, but as far as the amount of castings to add to your mix goes, I would suggest anywhere between 10 and 30% proportion. I’ve read a number of academic research articles (i.e. based on university research) that have shown that relatively little vermicompost/castings goes a long way. As little as 2-5% can have a significant impact on your plants – 10-20% is probably closer to the ideal. It’s important to remember that high quality castings are not the same thing as “compost”, and it is not really a “fertilizer” – compared to some amendments, the nutritional value of it is pretty low. I like to think of it as a growth promoter. If you take two potted plants and give both enough inorganic fertilizer to provide all their requirements, but also add some vermicompost to one of them, you will very likely see significant increased growth in the vermicompost treatment, thus demonstrating that the material has growth promoting properties above and beyond the nutrients present.

Coconut coir is a good option since it is apparently more sustainable than peat moss – it’s a waste product of the coconut industry, rather than something that is harvested (like peat). It is also neutral in acidity, unlike peat which is acidic. I’ve started using coir quite a bit this year (for worm bedding) and have been really impressed with it. To be honest, I don’t know what it’s like as part of a potting mix though – guess there’s only one way to find out.

Hope this helps!

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    • Tara
    • March 25, 2010

    After going thru college and grad school I am very research oriented and therefore am reading thru your entire site before setting up my bin (I am however getting food and bedding stored away). Since I am only up to June of 2008 I don’t know if this idea has been addressed, but I’m wondering if drying out the citrus peels would help with the limonene issue.

    • Aschwin
    • March 13, 2012

    For understanding why worms and their castings are good for the soil, I recommend reading the book “Teaming with microbes”. It tells about the soil food web and the combination of fungi, bacteria and crawlers like worms, insects etc.

    It thus depends on where the castings are used and if there is other ‘life’ in the soil that converts one or another so the plants can use it.

    The chapters about mycorrhiza are worth the book by itself.

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