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I have had bits and pieces of information about using rock dust in the garden scattered among my garden notes and in my books for years. Recently some neurotransmitters in my brain finally worked together and I had a really big DUH! about why I should use rock dust in my garden, and what it can do. It is all so very simple to me, finally.
Eons ago the earth had a mantle of rock. Then the glaciers slowly and inexorably moved and ground the rocks into a thick layer we called dirt. The dirt supported plant life, which took in the minerals needed for growth, and gardens were born. Over thousands of years, essential micronutrients were continually taken up by plants, often to the point of exhaustion. We as gardeners attempt to add nutrients back to the soil by means of fertilizers, compost and/or other amendments that we purchase and apply in vast and expensive quantities. However, those materials rarely contain all the micronutrients eroded away or taken up by plants.
What are Micronutirents?
“Eight of the seventeen elements essential for plant growth are micronutrients. On soils deficient in these micronutrients, the application of small amounts of these nutrients can greatly enhance crop production. The micronutrients are Boron (B), chlorine (Cl), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn). With the exception of nitrogen, all plant nutrients are of geological origin. Under natural climatic conditions the physical breakup, chemical weathering and release of nutrients from minerals is not fast enough to provide the nutrients for annual crop production.” [1]
There was an area of New Zealand where the sheep were dying for no obvious reasons – there was plenty of food. Then it was discovered that the soils were deficient in the element cobalt. It is well known that cobalt is needed for our immune systems. Another example is provided by E.I. Steifel, Science, 996, vol. 272, where he showed that the process that accounts for much of natural nitrogen fixation in soils requires molybdenum. In many soils adding a trace of Mo would reduce the need for nitrogen fertilizers. [2]
It has been suggested elsewhere that there are as many as 90 minerals needed by plants. Minerals are also essential for human health and the human body utilizes over 80 minerals for maximum function. [3] Because our plants and soils are so nutrient depleted, even if we eat the healthiest foods, we are not getting all the minerals we need.
One Solution
There is one simple solution: rock dust. Rock dust is generally a by-product of the gravel industry and is available almost everywhere, often free for the taking. Rock ‘gravel’ or dust is found in the bottom of creek beds, and pond settlings. The finer the size, the easier microorganisms can access the minerals but if the rock dust has been ground into silt, it is too fine and will merely clog up the pores in the soil.
The use of rock dust is not new. Agricultural research with finely ground and chemically unprocessed rocks and minerals, based on the concept of “bread from stones” started in the 19th century by Missoux (1853/54), Hensel (1890, 1894) and others. The Hardin Brothers in Queensland Australia have been using rock dust more than 20 years. They have found less environmental damage, 25% higher yields, 20% increase in growth rates and 80% less fertilizer. [4]
One reason seaweed is so effective in the garden is the high trace mineral content. Greensand, a common soil amendment, is just dust from sandstone rock that was deposited in marine environments.
How does rock dust work best?
Rock dust is most effective when mixed 50-50 with organic compost and a handful of soil to add some microorganisms. The microorganisms feed off the rock dust, taking only the nutrients they need while leaving the remainder in the sub-soil. The compost provides the medium for the microorganism growth. Optimally, the rock dust and compost mixture should be incorporated into the top few inches of soil if possible but may also be spread by broadcasting or spread by hand if you use a no-till method of gardening.
It is not totally necessary to add the rock dust mixed with compost. The dust alone may be added and raked in, or tilled in. The addition of compost just gives the rock dust a head start as food for the microorganisms.
An interesting benefit of adding rock dust is that it will help create more organic matter, which in turn helps hold the soil in place and conserve water. Soil erosion is an effect of the shortage of minerals to support the soil organisms. “That shortage can be made up on any piece of land in the time it takes to work ground gravel dust into the topsoil. When that is done, the soil microorganisms begin to multiply and it is they who prevent soil erosion by granulating the soil and holding it against both wind and rain." [5] What will Rock Dust Do for my Garden?
Applying rock dust is often called “remineralization” which actually revitalizes the soil by mimicking the process of glaciiation.
Rock Dust: Provides slow release of trace minerals Increases microorganism growth Builds more soil Increases nutrition in plants and crops Cuts the need for chemical fertilizers Increases water retention in the soil Increases pest resistance Increases crop yield Reports of increased winter hardiness
There is a wonderful photo comparing carrots grown in, and grown without rock dust here: http://prorev.com/dust.htm. Unfortunately I have not been able to locate the copyright holder to get permission to use the photo here.
What Kind and Size Rock Dust and How Much?
If the mesh that screens the rock dust is of the size “minus 200” (gravel industry standard nomenclature) it will work in your garden. Masonry sand and sand made for sand-blasting procedures are too coarse and will not be as effective in your garden, taking longer to break down. Rock dust from a gravel pit is usually unscreened but about the right size.
Locally, I have granite dust available from the gravel pits, which is okay to use but not best. The mixed gravel dust from the local stream beds is better. A better yet rock dust comes from glacial gravel or volcanic rock like basalt. Another is montmorillonite. Montmorillonite is a very soft phyllosilicate mineral that typically forms in microscopic crystals, forming a clay. It is the main constituent of the volcanic ash weathering product, bentonite. [6]
An application of 2 tons per acre is the minimum amount, and as much as 20 tons per acre for exceptionally poor, dry soil. Use about 14 pounds of rock dust per 100 square feet of garden bed (or 5 pounds per square yard). If this sounds too good to be true, try an experiment at home with potted plants: take a 6” pot filled with half soil and half peat. Add 3 tablespoons of rock dust. Do another pot just the same but leave out the rock dust. Put identical plants in both pots, and watch for astonishing differences!
I have a 'growing my own food' obsession that grew out of my overlapping interests in cooking, nutrition and gardening. I am also a teacher (but outside the System), a writer, and a builder… and a craftsperson and... and… and many other things, LOL. In fact, I guess I am a generalist.
I live in the southern Appalachian Mountains on a hillside with a creek in front and drive a 15 year old truck I lovingly call “My Farmer’s Ferrari.”
Posted by thethorinator (from Acton, MA) on April 7, 2008 at 3:37 PM:
Hi there,
Does anyone know the best or easiest way to locate "Rock Dust" of this type as we have a community garden and it would be intelligent, I would think, to till some into the topsoil before we plant our seeds this year? That would be awesome, thanks!
Sincerely,
Thor
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Posted by darius (from Marion, VA) on April 7, 2008 at 4:57 PM:
Thor, try a local quarry... or purchase some greensand at a good garden center. Unfortunately, greensand only comes in bags but a little goes a long way.
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Posted by darius (from Marion, VA) on April 11, 2008 at 7:43 PM:
Hi... just found this info. today on the Rodale site. You might try checking it out...
Quoted:
Worm Castings / Bat Guano / Glacial Rock Dust... these products will give amazing results! Try them and see for yourself... for info or to order... phone 734-667-2936 or e-mail [e-mail:rockdustgal@yahoo.com].
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Subject: Great Information
Posted by NatureLover1950 (from Vicksburg, MS) on April 7, 2008 at 1:27 PM:
Thanks so much for your very informative article. When we built our house, the lot had to be graded down by approximately 20 feet. Needless to say, I have NO topsoil and have been working hard for the last four years to get my vegetable and flower gardens amended with all that was lost. I will be on the lookout to see if I can find either greensand or rock dust.
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Subject: same as diatomaceous earth?
Posted by Sundownr (from Wytheville, VA) on April 7, 2008 at 12:52 PM:
Darius, your article was very informative, as always! I have one question though, is the rock dust you wrote about the same as diatomaceous earth? Or, is diatomaceous earth just one form of rock dust?
Thanks for the article.
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Posted by darius (from Marion, VA) on April 7, 2008 at 3:03 PM:
No, not quite, but mostly Yes. Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae. It is a naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder. This powder has an abrasive feel, similar to pumice powder, and is very light, due to its high porosity. The typical chemical composition of diatomaceous earth is 86% silica, 5% sodium, 3% magnesium and 2% iron.
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Posted by Sundownr (from Wytheville, VA) on April 7, 2008 at 3:18 PM:
I just wanted make sure. Thanks again Darius!
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Posted by sghfuller (from Grand Junction, CO) on April 8, 2008 at 1:08 AM:
Is white pumice powder ("coarse") of dental grade good for plants?
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Posted by darius (from Marion, VA) on April 8, 2008 at 9:44 AM:
Sorry but I have no idea.
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Posted by Sundownr (from Wytheville, VA) on April 9, 2008 at 7:23 PM:
I "planted" green sand today, lol. I got 3 of my raised beds prepped for planting, using the rock dust with the compost and manure. I'm anxious to see the results.
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Posted by darius (from Marion, VA) on April 9, 2008 at 11:19 PM:
Great! Be sure and let us know. My results with greensand in Asheville were not splashy, just slow and steady improvement. Where did you buy it?
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Posted by Sundownr (from Wytheville, VA) on April 10, 2008 at 10:11 AM:
A couple of local stores carry it, although at a higher price than what's been quoted by others from out of state.
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Posted by jlp222 (from Hammond, LA) on June 11, 2008 at 8:03 AM:
Sundownr - how did it work?
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Posted by Sundownr (from Wytheville, VA) on June 11, 2008 at 8:16 AM:
So far, so good. I'm late in planting some of the veggies I had planned, but the peas and onions are doing very well.
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Subject: Love it, another great "duh" moment!
Posted by doccat5 (from Fredericksburg, VA) on April 2, 2008 at 11:15 AM:
Great article, darius. I think this is one of those it's so obvious it's right in front of your nose all the time and you just don't get it. Thanks for sharing.
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Subject: great article!
Posted by flowrgirl1 (from Winston Salem curren, NC) on April 2, 2008 at 9:09 AM:
What a fantastic idea. I will have to utilize this method in the near future.
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Posted by Kelli (from Los Angeles (Canoga , CA) on April 2, 2008 at 4:18 PM:
Very interesting article, and a reminder to me to dig out the bag of greensand buried somewhere in my storage bin. And for those who aren't familiar with greensand, yes, it really is green.
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Subject: Rock dust - wow!
Posted by beth_donovan (from Easton, KS) on April 2, 2008 at 8:02 AM:
Darius, what an eye opener! I had no idea that the reason the weeds grow so big next to our gravel road is the rock dust. LOL!
That was a very informative article. Thank you.
Beth
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Posted by AYankeeCat (from Fairfield County, CT) on April 2, 2008 at 9:22 AM:
Living in Connecticut - I have a constant source of rock dust as I swear my garden is solid rocks and beating them into small enough pieces to get them out of the way makes lots of dust. The only scary thing is that people here say that the glaciers brought the rocks in the first place and they have gone back for more!
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Posted by beth_donovan (from Easton, KS) on April 2, 2008 at 9:58 AM:
I understand Yankeecat - we live in what are called the Glacial Hills of Kansas - believe it or not, it is hilly! And we have all kinds of rocks and boulders that the glaciers dropped off before heading back for the Artic!
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Posted by LariAnn (from Miami, FL) on April 2, 2008 at 10:09 AM:
This article explains a phenomenon I wondered about, and that was how plants grew at all in ground up coral rock down here in south Florida. Even in places where I would pound away at the coral rock to make a planting hole, plants would often grow better than expected there. I only wish I could get some northern rock dust to use for my soilless mixes!
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Posted by darius (from Marion, VA) on April 2, 2008 at 10:26 AM:
LariAnn, there should be some available in bags for you to use in experiments. I know the Thompson's sell it across the pond, and make it available online. [HYPERLINK@www.angus-horticulture.co.uk]
Author, Graham Harvey has done a great deed by bringing information about the need for remineralisation to his many thousands of readers in his latest book "We Want Real Food", launched in February 2006.
[HYPERLINK@www.amazon.com]
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Posted by LariAnn (from Miami, FL) on April 2, 2008 at 10:38 AM:
Darius,
Thanks for the links, although I don't think it would be practical economically for companies in the UK to ship rock dust over here to the USA. However, a quick search yielded the following, including links to many sources around the world, including the United States:
Thanks for bringing this very important information to the forefront via your article!
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Posted by carrielamont (from Milton, MA) on April 2, 2008 at 12:58 PM:
Wow - Darius, thank you, thank you. I have been investigating soil-less mixes myself recently for an article I'm working on, and I found your information to be not only timely but, well, DUH, great! xx, Carrie
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Posted by bluespiral (from Ellicott City, MD) on April 2, 2008 at 6:44 PM:
Excellent article, Darius - thank you
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Posted by cocoa_lulu (from Grand Saline, TX) on April 2, 2008 at 10:51 PM:
Thank you for your article. I read it this morning and bought some this afternoon. My local feed store had it. Texas greensand 7.00 for a 40lb bag, not bad for healthy plants.
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Posted by darius (from Marion, VA) on April 3, 2008 at 3:41 AM:
Wow, cocoa_lulu... now THAT's taking action!
Glad everyone enjoyed the article, Thanks!
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Subject: Wow, what a concept....
Posted by Sharran (from Calvert City, KY) on April 2, 2008 at 1:22 AM:
Darius,
My art/humanities/literary brain never assimilates scientific knowledge very easily or quickly. You just did something magic, because even at midnight I read your article and it makes total sense. This is something I never thought about, and never would I have believed that the use of rock dust would make that much difference in the growth of vegetation. Thank you for this eye opener.
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Posted by Dutchlady1 (from Naples, FL) on April 2, 2008 at 10:52 AM:
Who would have known. Thanks for the useful article.
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Posted by pirl (from Southold, NY) on April 2, 2008 at 2:39 PM:
Thank you, Darius, for a very informative and well written article explaining the benefit to all of us.
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Posted by melody (from Benton, KY) on April 2, 2008 at 5:11 PM:
Great article Darius. Well written and easy to understand. Thanks so much.
