More Fun with Rock Dust

A couple of weeks ago I reconnected with my rock dust supplier/friend Klaas, from Boreal Agrominerals Inc (formally known as “Agricultural Mineral Prospectors Inc”). Two years ago he gave me some of his micronized (ground really fine) “Spanish River Carbanatite” to “play” with (see “Fun with Rock Dust“), and while I’ve certainly put it to good use in a variety of ways (and have mentioned it multiple times here on the blog), I have yet to do any formal testing.

My renewed interest in rock dust is in large part due to the fact that I am working with European Nightcrawlers a lot more. They seem to be more sensitive to acidic conditions than Red Worms, so I’ve been thinking that a calcium-rich rock dust might serve as a valuable supplement for these worms.

The material Klaas left me with this time around isn’t micronized, so it has more of a sandy look about it, but I actually like it better that way. As you can see, they now have some nice packaging, and offer bags in multiple sizes. Klaas gave me a 10 lb bag and a bunch of the small “single serving” (1.23 oz) packets. I really like these new mini packs, and think these would be great for making batches of compost tea – just empty it into your bag of compost, submerge in the water, and away you go. They could just as easily be used for adding a sprinkle here and there in your worm bins (worm towers etc etc) as well.

Speaking of “sprinkling”…

I actually sprinkled some of the rock dust around the base of my recently-planted (at the time) tomato plants – they were looking a bit sad early on – and was amazed to see them looking much better by the next day! Apart from offering plenty of bio-available calcium, the mix is reported to offer a wide range of other nutrients and micronutrients – so I guess I shouldn’t be too surprised by the boost in vitality.

For my first “official” rock dust experiment, I am looking at the effect (if any) of the material on Euros in small plastic worm bins. I’ve kept things very simple for now – setting up two rock dust treatment bins and two controls. I filled each of these containers about 3/4 of the way with aged horse manure. I then added a small amount (used a little plastic cap) of rock dust to two of them. The contents in all the bins were mixed up well and moistened. Lastly I added two adult Euros to each one.

Initially I am simply letting the worms get settled in their new home. Sometime this week I will start adding some “food”. In this case I will be using pureed apples (I recently diced up and froze quite a few apples that were no longer good for eating). I will mix the apple with a small amount of rock dust for that treatment, and leave it as-is for the control. I may also mix in some coffee grounds. This is another material I happen to have lots of – and I’m just generally interested to see how the Euros do with it as a food.

I want to see if there are any differences in terms of growth, reproduction and overall health of the worms in these two system. At the end of the experiment I would also like to compare plant-growth-promoting properties of the vermicomposts produced in these bins.

If I might toss in one more plug for “Volcanic Minerals Plus” – since Klaas has been nice enough to give me all my sample material for free – I wanted to mention while they are still working on establishing U.S. distributorship for the larger bags (widespread availability up here in Canada, though), the smaller packs ARE currently available to U.S. customers. If you have an interest in trying out some this material, without breaking the bank, these are a great option. Just drop me an email and I will get you connected with Klaas.

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Euros vs Reds – 07-02-13

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Worm Inn vs Plastic Bin – 06-27-13


    • John W
    • July 2, 2013

    How are you testing it? What will the two worms show you? Are you seeing if they consume apples quicker?

    • Bentley
    • July 2, 2013

    Hey John,
    I WILL see if the food gets consumed more quickly, but this is actually more of a long-term project to see how it affects over all population development in these bins. Think of the two Euros as “Adam and Eve”.

    • John W
    • July 2, 2013

    Can there be much of a difference (obviously you are going to find out)? I am just wondering….I mean if a worm throws down a cocoon every X amount of time and there are X amount of worms in a cocoon…seems like there is not much in the way of variables.

    Will be interesting to see. And also it would be interesting to see how much money it cost to get the improvement that could occur. Would it be profitable to use the rock dust or just let the worms work slower? Or would the increased population pay for the rock dust in additional sells…Just the business side of me wondering that one.

    • Bentley
    • July 2, 2013

    The key thing to remember, though, is that worms DON’T just toss down cocoons consistently at a specific rate (although the number of worms per cocoon IS pretty consistent). It completely depends on their environment + various other factors. I’ve read before that calcium can actually help to boost reproduction – so it will be interesting to see if there is an increase in cocoon production in the rock dust bins. The buffering capacity of the material may also help to create a more optimal habitat for the Euros, thus helping with long-term population growth as well (they may suffer in the other bins since they will likely get more and more acidic over time).

    We shall see!!

    • Kim from Milwaukee
    • July 3, 2013

    Bentley, I’d like to see if powdered eggshells buffer the acidity like rock dust, since that’s what I normally use to keep the pH of my bins down (I love eggs). Do you know if it works in a similar way?? Not sure of the mineral content of shells and rockdust, but I’m thinking they might be similar.

    • Lynn
    • July 3, 2013

    I was wondering the same thing, Kim. I haven’t yet found a way to actually get the eggshells to powder, but I get them crushed pretty fine, and sprinkle over each feeding. The worms like them, but I still “feel the need” to add eggshells to the tomato plants. If I could use rock dust in the bin to balance pH and add calcium, DH could stop stressing over what to save when he peels those hard-boiled eggs. 😉

    • John W
    • July 3, 2013

    You can use a coffee grinder to turn egg shells into powder. I went to a local thrift store and picked one up for $4. Put 5-6 eggs in at a time and it turns them into the finest powder you can imagine in just seconds. Its actually scary to me because just lifting the lid off will cause a fine egg powder to come up. All I can think of is…”I hope there is no e coli in this powder”

    I use the Braun 4141 coffee grinder. I know you can pick them up off of ebay for like $10

    You can also use coffee grinders to crush fresh herbs and spices, but you might want to keep the grinders seperated!

    • John W
    • July 4, 2013

    That would be a good experiment Bentley. Maybe you can throw in one more cup to see if egg shell powder is comparable to rock dust?

    • Bentley
    • July 4, 2013

    KIM – My understanding of it is that the calcium in this rock dust is more bio-available than that in typical calcium carbonate (eg. ag lime) – and I wouldn’t be surprised if egg shells are even somewhat slower to give up calcium than the powdered lime. A big part of why I live this particular rock dust is that it contains all sorts of other nutrients (and micronutrients), so I think the vermicompost would end up being pretty stellar from a plant growing perspective (and the worms may benefit from all the minerals as well).

    All that being said, both egg shells and ag lime are great if you’re simply trying to buffer acidity – no need to get a fancy rock dust for that!
    Lynn – you’re right – one of the hassles of egg shells is getting them broken down small enough so they’ll actually break down. Even the small fragments seem to last a long time – I found plenty of them when I excavated my sandbox trench (they would have been there for likely 5 years or so). Something like ag lime or dolomitic lime are probably a good alternative – just don’t go too crazy with them, since higher pH can result in more ammonia volatilization.
    JOHN – Good call on the coffee grinder – or rather, a second hand coffee grinder (no need to get the spouse mad about egg fragments in the coffee – haha).

    Unfortunately our son is very allergic to eggs (Oh how I miss them – boo hoo!) so I don’t have shells to play with anymore. Do seem to be some that come with the coffee grounds I pick up though, so perhaps I can round up some of those.

    • chris
    • July 5, 2013

    Hi Lynn/Kim and Bentley.

    The secret to egg shells is you have to dry them out at a high heat first. put them in the back of the oven when you are doing a Sunday roast. They have no smell and will not taint the food you are cooking and will never CATCH FIRE!.

    Then just shove them in a blender or food mixer.
    Instant powder and all the calcium and minerals are still there.

    Great stuff.

    kind regards


    • chris
    • July 5, 2013

    Paying for rock dust!!! Bah!!!

    We call it river sand over here.

    Think about where it comes from?

    • Kim from Milwaukee
    • July 5, 2013

    Bentley, eggshell powder will dissolve in lemon juice. I’ve seen a recipe for homemade calcium supplement made in this manner. And many chicken farmers give the shells back to their chickens to reuse the calcium. I give it to my finches as well.

    I’ve cured tomato plants of blossom end rot with eggshell dust as well. It’s very easily absorbed by the plants.

    Chris, I allow my shells to air dry and they powder easily in my coffee grinder.

    • chris
    • July 5, 2013

    That’s the way kim!

    It is great stuff so is river sand!

    • Chris
    • July 5, 2013

    John W.
    I need to get something like that. I’ve been doing it with a mortar and pestle, which works, I get a super fine powder from it, but it certainly takes more than seconds. I think if I tried to put 5-6 eggshells in at once it’d probably take me an hour (too much at once just makes it harder).

    Just one thing to note, I’ve heard you should be careful not to inhale it. I’d probably suggest leaving it sit for a few minutes to settle before opening the grinder, or using a dust mask.

    • Bentley
    • July 5, 2013

    CHRIS – Cool tip. Thanks for sharing!
    As for paying for rock dust, while I agree it can get a little out of hand when some of this stuff ends up marketed as a be-all-end-all miracle powder, it’s important to note that the term “rock dust” is like “compost”, “manure” etc etc – it DOESN’T refer to one thing. There are infinite different kinds of rock dust – each with their own different composition. Some are beneficial for certain applications but not for others. Some are probably just useless across the board.
    Beware of marketing hype – yes – but don’t completely discount something just because someone is selling it.

    As for your river sand – that’s probably great stuff too (assuming the river isn’t badly polluted)!
    KIM – Cool. I think the key is to get it ground up fine enough. Whole shells and even the smaller fragments (as mentioned) seem to last for a LONG time. But then again, this could also mean that there hasn’t been a lot of acidity in my beds.
    Anyway – don’t mean to give the impression that I’m not a proponent for using egg shells (or am some sort of rock dust zealot – haha). It’s ALL good!

    • John W
    • July 5, 2013

    A lot of the times when I have turned the egg shells into powder with the coffee grinder I just dump the powder in one spot on top of the compost. The worms will actually come up and eat it like it’s the best rotten watermelon they have ever seen. I have seen a whole cup worth of egg dust be consumed in just a few hours.

    • Kim from Milwaukee
    • July 5, 2013

    Is it just me or does Rock Dust Zealot sound like a great band name?

    • Bentley
    • July 5, 2013

    LOL – either that or a quirky celebrity’s baby name!

  1. bentley, i’ve been working with rock dust & pulverized egg shells which i process in my bokashi before feeding to my worms.

    i’ve been seperating my systems so that i can test the resulting worm castings in order to know how to apply them to amend soils.

    so i have a large system full of expended coffee grounds, roughly 4 tons, 15 gallons of which i fermented with high test, 10,000 cps volcanic rock dust from ontario canada. (it’s the stuff that calvin bey uses – the guy who grew the butternut squash that won the high brix (nutrient density) competition last year.) i have several smaller systems with general food scraps. in august we can get the grape must from wineries & turn them into bokashi, which we can feed to the worms. we can get large amounts of this, which is good in terms of the cost effectiveness of testing the worm castings to understand what the quality of the output is.

    in any case, i’ve been trying to determine ideal ratios of pulverized egg shell & rock dust powder to add to my bokashi/worm food to turn out a more balanced result.

    international ag labs advises ideal ratios of n, p, k, ca, & magnesium. the major macronutrients.

    by far the most commonly deficient macronutrient & the one that is needed in the highest amounts, consequently conferring the greatest benefit to the health of plants is calcium. not always, but MOST commonly.

    according to jon frank of, international ag labs, the ideal ratio of available calcium per acre (43,560 square feet – to a depth of 6 inches [the typical soil test depth]) is 3,000 lbs.

    this translates into .3 lbs. per 4.356 square feet (to a 6 inch depth) or roughly .3 lbs. per 2 cubic foot. one cubic foot is the equivalent of one 5 gallon bucket filled 5 inches below the rim.

    basically, according to my calculations & knowledge level so far, this translates into roughly 2.4 ounces of available calcium per 1 cubic foot of soil as the ideal, until further notice.

    so, if using egg shells pulverized into powder, perhaps double or triple this per cubic foot would be a good balance if you use the worm castings as the bulk of a potting soil media, or a multiple of this if you dilute your worm castings significantly in your applications.

    as for rock powder, if you find out from your friend exactly how much available calcium is in his rock dust per lb. or per 100 lbs (as standard) then we can figure it out from there.

    rock dust is generall recommended at a rate of 1 lb. per square foot (to a depth of 6 inches) which would be 2 lbs. per cubic foot.

    lol.. math has never been so tolerable to me as it is now, having having worms, soil, & most importantly *nutrient dense food* as my immediate goal.

  2. it would be interesting to determine exactly how much available calcium is produced per lb. of powdered egg shell AFTER the worms have consumed it.

    naturally it’s far less available to the plants prior to worm processing.

    • Lynn
    • July 5, 2013

    I vote for baby name! It’s just as good as Blue Ivy.

    Kim, blossom end rot is what caused me to start saving eggshells to start with, long before keeping worms showed up on my radar. Haven’t seen any rot at all since we started two years ago. For that, we just kind of crumble, I guess about 1/8″ or so pieces and use as top dressing. Crushed egg shells are also golden when it comes to keeping slugs from eating Hosta leaves, so a ring goes around those too.

    DH is not going to understand why we have a coffee grinder when I buy coffee in cans….hehehehe

    • Bentley
    • July 6, 2013

    Jonathan – the stuff I am using is also “volcanic rock dust from ontario canada” – haha. I don’t imagine there would be more than one that fits that description, but perhaps I’m wrong? Where did you buy it?

    Anyway, thanks for chiming in!

    • Oneman
    • July 8, 2013

    Hi Jonathon.

    You lost me at amp’s~??? I understand your passion to learn and log thinks, but you have gone beyond the pale mate. Love what you are trying to do but i just do not understand.

    Can you clarify please. In English

    • Oneman
    • July 8, 2013

    I had to look up bokashi and i am still no further forward. Sorry.

    From Wikipedia, the free encyclopedia
    Look up bokashi in Wiktionary, the free dictionary.
    Bokashi (???) is Japanese for “shading off” or “gradation.” It may refer to:
    Bokashi (printing), a printing technique
    Fogging (censorship), blurring an image as a form of censorship
    Bokashi composting

    • Oneman
    • July 8, 2013

    Hi Bentley.

    I was brought up in a north east coal miners town and the only other job option was the brick works. they had a big hopper there that was full of steel ball bear, about the size of your fist ( base Ball) They where used to crush up miss shaped bricks, to re use.

    They also did aggregate for drive ways and road surfacing. Huge rocks from all over, where poured in to the top and the ball bearings did the mashing. The stuff you are paying for in bags is the stuff that spillt out of the sides!

    Still good stuff though. use it. Better still go to your nearest quarry and bag your own. permitting you have access of course. Wink!!! Its the stuff that falls off the sides of the conveyor belt. It looks like piles of rock dust!!!! and its free if you ask and bag it.

    • Bentley
    • July 9, 2013

    Oneman – again, the key here is to remember that “rock dust” does not refer to one thing. Even “volcanic rock dust” could refer to countless different materials. Rocks can be composed of many different minerals in countless different combinations.
    I can pretty much guarantee that the stuff I am using is NOT the same thing you are referring to. Not saying that material is lower or higher quality – just emphasizing the fact that it is absolutely DIFFERENT. If someone said “shale rock dust” that would be pretty specific, and it would likely be quite similar to other shale rock dusts. But some rock dust of unknown composition in the UK won’t likely be exactly the same as a rock dust that comes from an ancient volcanic deposit of carbonatite in Northern Ontario. lol

    It completely depends on the composition of the parent material.

    • Steve
    • July 29, 2013

    Something interesting to note when using rock dust to improve mineral content. The world’s oldest, healthiest people live in areas where they drink “glacial milk”. Highly mineralized water from existing glaciers (that has pulverized rock over eons) used for drinking, livestock, & vegetables. Referenced from “Dead Doctors Don’t Lie”, by Dr. Joel Wallach & Dr. Ma Lan. By providing your worms a highly mineralized diet I would imagine you would provide a better substrate for more nutitious fruits and vegetables.

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