The many benefits of rock dust

Here's another source for mycorrhizae.

http://www.fungi.com/mycogrow/index.html

I bought their MycoGrow for Vegetables, which is available in one ounce packets for $4.95. A little goes a long way in my container garden. I haven't been using it long enough to know how well it works.

Forgot to mention that I add a few scoops of greensand to my potting mix when planting each container. I bought a 50 lb bag at my local nursery for about $20, and it will probably last me 3-4 years.

Greensand is recommended in the fabulous book "The Bountiful Container" by Rose Marie Nichols McGee and Maggie Stuckey. If you don't already have this book, you need to order it ASAP. My copy is dirty and beat up because I always have it with my when I'm planting!

Anybody know of a local supplier of Azomite in the Houston area?

Thanks, I added the myco-links to my notes. I like that they list which species are in each of their products.

Funny that most of their products are mixed ecto & endo ... but like you, I would get the all-endo stuff.

Corey

Would Builders sand" have any value as "Rock Dust"???/

How about the coarser version--with actual small stone bits mixed in,
that is used as an underlayment for pavers?

Asking--as both of these are easily available in Box Stores...

How about Granite dust...also sold in Big Box stores?

I just had a raised bed built--and will be filling it with delivered top soil.
Will be adding semi-composted, shredded leaves and some of my own
compost near the surface.

I DO NOT want to spend $$$$ for having to buy anything on line....
My soil will be--what it will be.....

Looking for very cheap alternatives....

Thanks, Gita

Builders' sand: nope. Coarser sand: nope. The individual pieces are too big for microorganisms to use easily, and they're not made of a wide variety of minerals. Not much good, even if you were to pulverize it to powder.

Granite dust: probably decent. As the original article puts it:

Puddle....

I have NO idea where here I could get any of it......never even heard of ir until all this talk here....
I will just go with the good ole Top Soil amended with my leaf compost.

I don't think any farmers of gardeners here use any of that "dust/gravel stuf"--and things still grow...

Thank you all for your suggestions and explanations.
It has been educational....and will stay in my mind.....I appreciate it...

Gita

The granite dust should help somewhat. Sure, it's not perfect. But whose garden is?

I don't think real "sand" contributes useful mineral nutrients, because I think sand is just fine quartz (silicon dioxide). No matter how fine it is, there just aren't any good mineral ions in it to be leached out.

On the other hand, COARSE sand does help drainage and aeration somewhat, especially if it is big enough to be called "grit" (say, 1-4 or 5 mm).

Crushed ROCK ought to offer some minerals, depending on the source rock, and I gree that volcanic rock ought to be richest.

For minerals, the finer it is crushed, the better (down to dust).

For drainage and aeration, the bigger the better (up to around 5 mm or almost 1/4", I would say.

And big crushed rock is much better than coarse sand for this becuase grains of sand are mostly close to cubical or spherical. They tend to pack down compactly with very small open spaces. Crushed rock grains have irregular shapes and sharp points, and tend to be surrounded by larger void spaces than sand grains.

My belief is that sand - even as small as medium - helps heavy clay soils to be more friable (tend to break apart instead of becoming one big continuous airless pudding) - if they have at least SOME organics in them, like compost, leaves, clippings, sawdust or manure.

Clay with sand and little compost is still very prone to compaction and being hard when dry. Heavy clay just NEEDS composted organics and avoidance of compaction when wet, or nothing much will help it.

That's the belief I've come to over a few years of struggling with very heavy clay, and a cheap nature, and almost no free sources of compost.

If the soil doesn't have pretty decent structure, micro nutirients and even macro nutirents won't do much good. Roots can't pentrate airless soil, flooded soil, or very-heavily-compacted soil.

Once the soil structure is at least half-decent, micronutrients from rock dust are great, and one of the few things you can add to soil that will be a permanent improvement. And rock dust is probably better than highly concentrated soluble micronutrients - I doubt if you can overdose a soil with rock dust!

Crushed rock excites me more as a way to improve drainage and aeration, than as a source of nutrients. My soil NEEDS much-improved drainage and aeration BADLY! I am guessuing that my high clay content probably already has a fair amount of this and that mineral. And all that clay is tenacious about holding onto any ions that I bring in as I add compost and mulch.

Corey

I use a recipe for fertilizer,made with bonemeal ,bloodmeal, and greensand.well just started using 2 years ago...You have mentioned some very interesting things.I definitly ,will be adding greensand to my flower pots ,cant wait to see if there is a difference.i didnt know how beneficial rock dust is ,and Important .Makes great sence now.Thanks

I have four locally available source of free crushed rock. I picked up six five gallon buckets from the first source the other day and it is much like sand. The other sources said there's was larger than the industry standard of 'minus 200', which according them it contains chips as well. I am experimenting with some rogue tomato plants today making a potting mix which includes these crushed rock fines, wood chip fines, well aged cow manure, some spent worm media and pearlite. Will see how this goes.

I have been thinking of getting some rock dust from a monument place that's nearby. That's where they carve headstones for grave markers. It might be free or at least cheap. Any thoughts on whether that's a good choice?

The kind of dust matters a lot. I don't know if marble dust is worth using or not. According to what I've read, glacial rock dust has a good variety of minerals. Granite dust is so-so.

If the monument place can give you several kinds of dust from different types of stone, go for it.

Thanks Puddle. Another thing I have wondered about is lava rock. It is used around here sometimes as a mulch. If I could crush it somehow, would that be good for minerals? Without the crushing, do you think it makes a mineral contribution in the garden?

All rocks will weather, even boulders. Lava rocks will add some minerals, I guess. The smaller the pieces, the faster it'll weather. From what I remember, though, lava sand is used more often for its porous structure or for its attractive color, & not for its minerals.

My guess is that anything porus will be crumbled faster by frosts than solid rocks.

(I would say that "new" volvanic minerals have more garden potential than "old" eroded fines, but anything crushed is "new".)

I've also read the suggestion that if you buy crushed rock, you'll get "more minerals" from volcanic rock or "mixed" sources like crushed river gravel than from one rock type like granite.

But I don't really know. Wouldn't a sedimentary rock already contain a lot of variety?

I personally worry more about soil structure, drainage and aeration than micronutrients, on the theory that I would worry more about drowning than vitamin deficiency.

But if you have pretty good soil, rock dust for minerals is a great potential improvement, and long-term.

I like the idea of adding coarse pumice or tuff for structure & drainage, then counting on it breaking down over decades for minerals.

Corey

Mycorrhizae seems to be the latest gardening fad. It's not cheap and you don't need it IMHO. Just make sure your soil PH in in the right range for what you're growing. Since I can't find rock dust here I use greensand for trace minerals. Keep adding compost and organic matter to your soil and you'll be just fine!

I need to work on my compost pile,thanks for the Nudge..LOL..Great Info...it is soo hard to really understand ..I keep trying ...LOL

I agree that, if you have lots of compost, you probably have at least SOME of everything you need.

>> I would worry more about drowning than vitamin deficiency.

If I ever get all my rasied beds amended to the point of having good drainage and aeration, and plenty of organic matter ... then I WILL worry about micronutrients. But I'll have to find a cheap source of soil analysis.

My suspicion is that, with all the clay I have, micronutrients will be the least of my problems. But you never know, until the soil test comes back with something like: "you have a HUGE boron deficiency", and a tiny pinch of something makes everything grow twice as green.

Or, worse, "you have an excess of XYZ, so Iron and ABC will be insoluble and unavailable, good luck!"

Corey

You said it corey,makes my head spin....i have so many different beds,i would have to have the soil tested in every bed ,that would not be very cost effective ..LOL

>> i have so many different beds,i would have to have the soil tested in every bed ,that would not be very cost effective

I've begun thinking that I should take every opportunity I have to mix up the soil in my different beds. Well, at least spread some soil from my better beds into the worse ones, and remove soil from the worst ones and cycle that through my "dirt pile" where i screen and mix with amendments and compost.

Part of that would be to spread good soil microbes into the poor soil. Part would be to average out the weaknesses, so that one sample taken from the three biggest beds, plus one taken from my dirt pile, would be informative about the whole yard.

Mainly, I'm in doubt about pH. There's no doubt in my mind that everything is low in N, P, K, organic matter and iron. Probably low in sulphate and Mg. Too much clay, not enough sand and grit.

Corey

Im not going to do all that ...LOL... I do try to amend as well as I can ,its kind of the survival of the fittest.. I will stick to using my organic fertilizer and hope for the best. I have yellow clay or Had,talk about live an learn...I dug a lot of it out and replaced it,way too hard to try to amend it enough,I do cut a little in every now an then.Ive had to add sand in a few areas. Ive been using Ironite a little too,our soil is a little acidic here,not bad.But Im sure my soil is all confused .Like Me....LOL

One good thing about having "patchwork soil" - if it's different in every bed, each kind of plant can tell you what it likes best, if you scatter some seed or divisions around.

Corey

Corey if you need sulphate and magnesium, you might like some epsom salts (Mg sulfate)

I agree that epsom salts can be handy for sulphate, though dolomite lime is my preferred source of Mg. I've always lived where there was acid soil. Maybe under the Rhodies and Azaleas!

I worked at a place once, where they used several 50 pound bags of industrial grade ferrous sulphate every week. I scooped up a jar to supplement chelated iron fertilizers (that was for indoor growing).

When petioles got purple, I would water or spray with both iron and Mg. Why try to figure out which was the problem, when curing both was easy?

Corey

Petioles of what- Azaleas and Rhodies, or others?

You now chemistry better than I do- my soils is already acid so I don't expect I need sulphates for my azaleas. And then I don't feel they would want lime either. Whats a gal to do?

Yikes----

I sort of had forgotten about Epsom salts---so, after you mentioned it,
Sally, I went out and sprinkles some around everything....
My Brugs-(I know they like it), my tomatoes and beans and squash
and everything else, Just a couple TBS each.

Hope I did not screw up??????? I tend to do all--or none......

Gita

For those Canadian gardeners in Ontario I just picked up a couple of bags of 'rock dust' from GLOBALREPAIR.ca.

They call their 'soil conditioner' product "Rich Valley"http://www.globalrepair.ca/fertilizer.htm.

And I quote from their website:

"Contains rare volcanic, metamorphic and sedimentary minerals, calcium, rock phosphate and humates,..."

rouge... that sounds like a lovely mix!

I ordered my rocksand just now from planet natural, it was cheaper total than amazon. I got some espoma green sand today from a store.

I only have 7 raised beds and a compost heap, I figure 100 lbs should get me started. I spread the little bag of green sand in the beds just to get a start. I planted my winter greens today.

I put a moderate amount of Azomite on the gardens last year. It comes with an analysis. It can be picked up at dealers in some areas or ordered from Fedco Seeds/

http://www.azomite.com/

This message was edited Dec 6, 2011 4:39 PM

I got my rockdust and added it to my soil and compost heap. I didn't add it all at once since I already had seeds in the ground. I top dressed and side dressed, then I watered it in. I applied it more than once.

I don't have much of a winter garden, just a few greens, so I probably won't be able to see the effect till later this summer. I have noticed that my soil does not dry out nearly as bad as the last couple winters. I struggled to keep my swiss chard bed damp enough but it's easy now! It's like the soil is more wettable, plus it doesn't go through as fast. I thought it was my imagination at first.

I ordered some azomite last week. I figure it's best to have additives from a few differant sources. I'm planning on ordering more rock dust this spring as well.

Margo, one of the amazing things about greensand (and I still don't understand how it works) is that it loosens heavy clay soil yet will help sandy soil retain water better.

I got a couple little bags and put that in already, like I said, I'm diversifying my soil ammendments. I'm going on the notion that it is unlikely I would use too much. I have 5 10ft raised beds and 2 4x8 raised beds. Plus my compost heap. I have enough soil in my beds that I can remove some to put in fresh compost, I'm going to start putting extra in my front yard.

I got 100lbs of rock dust and have only used half on one bag so far. That gives you an idea of how much I've used. I would have thought it would have taken much more to have that effect.

I wonder if it's possible to use too much? I'm planning on adding it all when I redo for my summer beds. That's why I want to get extra to add. It's my understanding that it degrades very slowly, so adding a large bulk at once will last a long time.

Not that I've ever read.

Whats the difference between rock dust and greensand ?? Tamara

There are many types of rock dust. Each area around the country, or the world, has different kinds of rock and sediment layers. The greensand from New Jersey is largely from ancient marine layers.