I'd like to hear more about 'expanded shale'

JAMc_CA(z9 CA)April 8, 2005

Jacque_E_TX mentioned in a couple of posts that she is using "expanded shale" instead of vermiculite now. Jacque, or anyone else with knowledge of this, I'd like to hear more about it - such as:



where to get it (if I decide to try it)



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Jacque_E_TX(Z 8a N Cent TX)

Howdy, JAMc! Glad to *expand* on that shale for y'all.

Expanded shale is like "Vermiculite plus"--it is, as I understand it, "popcorned" shale rock.

Please realize that vermiculite is expanded, or "popcorned", mica. Mica is naturally a rock made of many fine layers--all fragile and glassy (silica rock is, basically, glass--so you have whisper-thin layers of glass puffed out, mostly apart). When expanded, mica forms a very fragile accordian shape that holds a lot of moisture--and usually some air. The air is needed to keep roots from drowning--they have to breathe, too! Alas, mica breaks down quickly into tiny blobs that can form a gray mass of blech -- say, if used at the bottom of a container. Even if the blobs are evenly distributed in your dirt-free soil mix, they still won't hold air anymore--and don't hold much water. Blobby mica is not a sterling aid to roots anymore. Solution? Add more vermiculite (at an annual cost), try another product/substance/method, or move to expanded shale.

Unlike mica (which expands into a fragile accordian shape to make vermiculite), shale starts as a roundish rock. Expanded shale retains a smooth rocky appearance--just larger. (Think of corn expanding into hominy--still a distinct shape, but bulkier.)

What is so wonderful about expanded shale? Expanded shale *always* retains 30% air. Even if you dump it into a bucket of water, the stuff still retains 30% air (in normal environmental conditions). This means your plants'
roots always have access to air, so they are pretty much drown-proofed. Texas A&M tested solid clay soil, in a ground-level bed, with moisture-sensitive plants. Solid clay soil slew the poor test plants rapidly (as anyone with clay soil already knew.....) The plants in the bed with expanded shale survived and *thrived*--that 30% air pocket content saved them. Naturally, the 70% water pocket content provides needed moisture to plants, even in challenging conditions like raised beds/containers in 110+ degree F summers. (Probably great for vacation survival for houseplants, too. Also for people with "blue thumbs" who overwater everything....)

Expanded shale is easy to use. It is useless to put a layer of expanded shale in the bottom of a container--just mix it evenly in the soil. The A&M experiment was 50% clay, 50% expanded shale. Your good compost/coir (or peat, or varied, aged compost only) soil mix will not need that much shale.

Unlike the water absorbing gels, expanded shale will never swell or shrink, so you don't have to worry about the soil (and plants) heaving up or collapsing.

I got mine at a fine plant nursery in Dallas, Texas called Northhaven Gardens. The brand name is TruGro Soil Conditioner.

Expanded shale weighs more like lava rock than vermiculite--and has the same ability as lava rock to remain intact for many years (centuries? millenia?) at a moderate initial investment.

Can you introduce expanded shale into your squarefooting program gradually (and spread the initial cost of 8-10 U.S. dollars for a bag the size of a large sack of compost/hummus/soil)? Yes. I think you could gradually mix expanded shale into your squares along with your new scoop of compost, each time you replant. An end result of 25-33 % expanded shale should be very beneficial to your squarefoot beds or containers, whether raised or in ground. I'm sure that even 1-15% would give a definite benefit to most gardens.

    Bookmark   April 10, 2005 at 10:54AM
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Riff(z7 NorthernVA)

Jacque, thanks so much for that info -- very interesting. I'd never heard of it before.

The study linked below seems to indicate that it helps when soil has a high percentage of compost, but may not help with other (loose organic) mixes. They didn't test clay soils.

Here is a link that might be useful: Another interesting test

    Bookmark   April 11, 2005 at 1:18AM
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Ray_Scheel(z8b/SS31 E. TX)

Riff: Interesting article.

I find myself wondering if the lack of benefit in the pine bark samples is because of the way fresh pine bark also holds air. In a small continer setting, its hard to drown anything in a pine bark mix, even when watered heavily on a daily basis.

I'm about convinced I ought to go get a bag somewhere and start working it in (or just scater it on top and let it work down as I top off). However, I'm going to give a recent massive earthworm transplant a chance to work to loosen things up a bit before trying anything else.

    Bookmark   April 11, 2005 at 9:52AM
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Riff(z7 NorthernVA)

I've no experience with pine bark in containers, but that makes sense to me.

If I start a new bed for next year I might give it a try instead of vermiculite. If I can find it, that is!

    Bookmark   April 11, 2005 at 8:49PM
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Ray_Scheel(z8b/SS31 E. TX)

To be clear, its expanded shale I'm thinking of getting a bag of.

Around here pine bark is easy to come by, I've got sevearal acres of woods and there is always a dead pine osmewhere shedding bark. FWIW, pine bark breaks down pretty quickly once it starts holding water - by the third season in a pot it is mush.

    Bookmark   April 12, 2005 at 12:08AM
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Riff(z7 NorthernVA)

Ooops! I knew what you meant, but I was unclear, too -- I meant the expanded shale, too. Since it appears to be produced out west, I wonder wether it's available here. I've never seen it, but never looked, either.

    Bookmark   April 12, 2005 at 4:49PM
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I live in San Antonio,and have an area in my backyard that (when it does rain) retains water due to the thick clay soil.

Nothing will grow there that I've tried (although if we have another rainy season I might try establishing a rice paddy).

I'm wondering if this stuff might be my solution. It's a large area roughly a 50 foot circle. How much of this stuff would I have to buy...would I 'till' it in or just dump it and cover it with soil? I wouldn't want it to simply wash away but if I could get that one area 'fixed' it might save me a fortune since the wife is now talking about putting in a 'water feature'...i.e a pond/mosquito haven..

Michael Main

Here is a link that might be useful: The Main Point Blog

    Bookmark   January 28, 2008 at 8:38AM
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Hi, Micheal. I enjoyed your blog on the Dish Network. You can tell them that I was a potential customer they lost. lol

About your backyard, expanded shale might be a help, but I think there are other cheaper and better routs to take. And there are issues of grade, slope, and drainage that must be corrected in your case.

I don't think I have enough info now to make suggestions. Homeowners will call many different soil types clay, and so there can be a big difference in what treatment will work best. You may need to perform some tests to see what you have.

As for the drainage, in the graphic below I show your property with a swale drain(red) near the back property line. Is there a fence or other obstruction to prevent the water from flowing into the field? At times of excess rain does the water leave your property near the middle of the back line or near the back left corner as seen from the street?

It would be useful to have photos taken from the spots shown in green such that your house is seen on one side of the photo along with the yard.

    Bookmark   January 28, 2008 at 3:05PM
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sinfonian(U8b A2 S5 SeaWA)

Ok, so why does the SFG book say with 1/3 vermiculite, 1/3 peet and 1/3 compost, all you EVER need to do is put a bit of compost on top when you replant? If vermiculite breaks down and you must add more, wouldn't Mel have figured that out in 25+ years of research?

I'm not suggesting shale isn't good. I'm just curious.

Here is a link that might be useful: Sinfonian's garden in progress...

    Bookmark   January 28, 2008 at 10:07PM
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rj_hythloday(8A VA)

Nothing in over a year?

I wonder if this is expanded shale, they don't actually list the ingredients, but claim it's a one time application. I've seen it at the nursery for $22, the same as I'd pay for coarse vermiculite in a 16lb bag.

''Soil Perfector is made from a naturally derived, ceramic mineral that is kiln-fired at temperatures in excess of 2000''

    Bookmark   February 27, 2009 at 11:12PM
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No..that is not expanded shale. It's actually turface rebagged from what I remember. It's a clay, not an aggregate.

    Bookmark   February 28, 2009 at 4:38PM
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Hello! I'm new to SFG this year, I remember reading about 'Zeolite' (apparently a term with plenty of applications) and wondered if it would work in place of vermiculite. It is described as 'a 100% crushed volcanic rock' and is promoted as a soil conditioner. They claim it has water & air retention properties... (it is at the bottom of the list on the left side of the web page).

    Bookmark   March 1, 2009 at 9:57AM
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jbest123(Zone 5 PA)

I have had a bag of Soil Perfector for several Months now. I cannot find a local source of coir or Michigan peat though. If I could, I think that along with HM compost would be the perfect potting/seed starting soil.


    Bookmark   March 1, 2009 at 5:03PM
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If you guys have Fred Meyer out there, they are now carrying coir for the same price as peat. Just fyi.

    Bookmark   March 1, 2009 at 7:34PM
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jbest123(Zone 5 PA)

The only Fred Meyer around me is a plumber???

    Bookmark   March 1, 2009 at 8:05PM
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Hey, Carolyn...I have a Fred Meyer! At least I will have, when I get home.

And mine isn't a plumber ;-)


    Bookmark   March 1, 2009 at 10:48PM
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Zeolites are molecular sieves, crystalline materials with a porous atomic structure. The zeolite's nanoscale pores provide an immense amount of void space. In addition, the void space exhibits an ionic charge that allows it to bind water molecules conditionally. Zeolites can hold water very tightly, but will release water readily in response to subtle environmental changes.

In industry, zeolite beds capture water from wet gas streams. At several atmospheres of positive pressure, a zeolite will bind the water content in a gas stream, allowing the dry gas to pass. Zeolites have large surface areas and a large capacity for adsorption. However, when the pressure is dropped, just slightly, zeolite can quickly release this same water content. The equilibrium condition toggles based on a minor pressure adjustment.

The benefits of zeolites are (1) a high holding capacity, (2) a tight binging of water in wet environments, (3) a rapid release of water in dry environments. Furthermore, these materials are durable and their porosity is molecular. When the material is crushed, it reveals additional surface area.

Expanded shale is not a true zeolite. It is a haydite material, possessing the same crystalline structure but lacking the ionic interactions. The absence of ionic exchange is not necessarily a bad thing. It seems true zeolites can force salts out of the water (hence the sieve term), while haydites do not exhibit enough ionic potential to squeeze salts from solution. At high salinity, water won't enter the haydite; it will flow from the haydite to dilute the salt.

I've attached an interesting article on "bonzai mediums", including mediums that behave like expanded shale. The applications may seem very specific, but the article details a plethora of sophisticated soil amendments.

Expanded shale looks like a great product. I'm down the street from a major producer, and I'm tempted to drive over and ask them about it. A local garden show, Gardenline, has verified that expanded shale can be used as a topdressing on existing lawns.

Has anybody used shale for amending hard clay and turf drainage issues? I'm looking for a top dressing recipe and a rate of application.

    Bookmark   May 31, 2013 at 9:13PM
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