bentonite clay

bentonite clay has great water retention ability and minerals how about this instead of vermiculie? and it is about 12to15 bucks for 40#or50# bag it has lots of uses you can even use it on your face and teeth and drink it so it must be safe and it is mined in the west. I think it retains 10x its weight in water sounds good to me

Hi Heavyhauler, to the SFG Forum.

This is a good question. Clay, sand and rocks are not equal to vermiculite and really are the last thing I would be putting into my garden growing mix. These substances offer very little by way of nutrition for plants and reduce the tilth of the growing medium. Vermiculite on the other hand holds water, easily exchanges micoro nutrients and allows air in the root area, which is why it is used in Mel's Mix. 

Here are a few informational links about vermiculite and soil amendments.

http://www.vermiculite.org/pdf_word/Vermiculite_Horticultural_Brochure.pdf

http://www.thesoilguy.com/SG/SoilAmendments

http://www.schundler.com/hort.htm

Dear HeavyHauler,  First, Welcome to the Forum!

Second, bentonite clay:

Do not add it to your mix.  It would ruin it.  As a retired health inspector, this was my experience with bentonite clay.  It is a safe material to use as a sealer around drinking water wells.  Let's use a 4" (pipe) water well as an example.  An 8" hole is drilled to desired depth.  A 4" pipe is inserted into the hole, leaving a 2" open space all the way around the pipe, the annular (from anus) space.  In order to keep contaminated surface water from running down this space to the clean ground (subsurface) drinking water, the space has to be filled.  The lower space is filled with tiny rock fill, just poured down until it reaches a certain depth from the surface.  This varies in CA from a minimum 20' for private homeowner wells in normal dirt conditions, to 50' or 100' or even 100's in the West valley Corcoran clay (long story there).  So the materials of choice are wet mixed cement or dry bentonite.  Wet cement is pressure pumped starting at the 20' (or what ever) mark, until it just starts to flow out the top of the annular space.  Sometimes a frame for a cement slab is in place and the cement continues flowing until the slab is poured.  End of job.  For dry bentonite, it can often be dry poured into the 20' space (or what ever) if it's not to deep.  Just left in that condition.  First rain, it gets wet and swells, forming a very thick clay seal, just as nasty to touch as pipe dope.  Your shoes become nasty, glucky if you walk in any. If you touch it, you just can't dry-wipe it off.

Transferring this knowledge to using it in Mel's Mix spells disaster.  Perlite and vermiculite will absorb and hold water and nutrients when wet.  But they don't swell because they are "popped" rock.  They just sit there absorbing and releasing water and nutrients and allowing air pockets.  Bentonite would swell, make a sticky, pasty mess of the Mix, squeeze out the air, and offer no benefit, only disaster.

I know vermiculite and perlite cost money up front when first making the Mix for a Box, but it is a one time expense, and just makes the Mix wonderful.

My first thought is that bentonite swells so much and then as it drys it trys to stick together as it shrinks.  It literally swells 10X when fully hydrated.  As it drys deep wide cracks develop in the soil that can literally rip plant roots.  It is part of my native soil.  So I would be cautious about how much is added into a soil mix.  I balance its natural presence in my soil with a bag of sand/12sf and lots and lots and lots of compost. 
It has its pros besides water retention, it is highly chemically active (has  and a great source and channel for minerals and organic chemicals.  It is alkaline.

So to totally lose the KISS admonishment~ I have been running my google finger a bit on this.  Bentonite and Vermiculite are both montmorillonite clays with similar properties.  The vermiculite in Mels Mix has been fired which expands it and holds it in that expanded form.  Thus the whole swelling and collapsing and making a sticky mess thing is taken out.  Apparently fired bentonite  has such a tiny particle size, which is not going to make it as good in a mix for us.  Unless it is what they call arcillite, which apparently is used a lot in aquariums and also bonzai growing but it seems very expensive.  Perlite appears to be a volcanic glass that is fired to puff it up.  Sources are Wiki and aguaculture links

What is usually regarded the best soil for gardening/farming is sandy loam.  Here is the soil triangle for contemplation of such and contemplating how Mel's Mix is trying to roughly duplicate this.  Note that clay is 0- 20% of sandy loam while sand is 50-85%, and silt is 0-50%. 



And now an article with reasons to use bentonite in the garden. http://www.no-dig-vegetablegarden.com/organic-garden-fertilizers.html There is also something I saw about Thai farmers using bentonite to help build soil and beach sand that has a coating of bentonite is what makes good castles.  I could spend all day following this around the internet.

Read about Fort Benton USA it was re constructed several times as it was on Bentonite clay ( montmorillic clay ) .
Whenever it rained for long the clay formed a gloopy glue & the fort walls fell down.
Yet in summer when the re constructions were made the post holes were as good as concrete apparently.


 Bentonite in MM would to my mind  make it a clay glued fiberous paste and not the sort of thing that plants can grow in as / when it dries out  ... it would be like asking plants to grow in concrete .   I also suspect that as the MM was worked and watered well the liquidized gloop would migrate to the bottom of the bed leaving a drying mat of clay and decaying veg behind  that would be hard to work

 One of the basic ideas behind the whole concept of MM is that it is light to work & full of air that enables well made compost to decay further .  Thus giving plants a nice long slow release of nutrients after the initial high rate of release when the compost is first added to replenish a bed from which an individual  square or two  has been fully or partly harvested. .


 Fully dissolved clear Bentonite is however good for clearing the yeast haze out of beers & wines

 It is often bade as a thick paste dried and ground to into granules then used ins animal litter trays soils to soak up urine and other liquids .

It is also supposed to be very good in coarse powder form called , "Fullers earth " for use in BIO CHEM warfare personal decontamination  as a, "  Bang , Blot & Rub "  device to try and remove chemical agents off your skin & equipment before things get too far out of hand .

plantoid wrote:Read about Fort Benton USA it was re constructed several times as it was on Bentonite clay ( montmorillic clay ) .
Whenever it rained for long the clay formed a gloopy glue & the fort walls fell down.
Yet in summer when the re constructions were made the post holes were as good as concrete apparently.

Cool, I never heard that story about Ft Benton before nor did I make the connection between the two, though for sure there is a lot of bentonite all through here.  It makes a ferociously sticky gumbo mud when wet.  I live at the head waters of the Missouri river and Ft Benton is 200 miles down river (north) where the river hit the ice during the Ice Age and made a hard right turn.  The fort was the end of the steam boats route up the river (think Mark Twain).  It started as a trading post and was bought by the army later.  It was originally log and then remade as adobe, maybe for the problems you read about?
Any rate, my instincts agree with you and sanderson but that article link I posted suggested in small enough amounts it can be quite useful.  We hear about MM being too thirsty in arid climates.  I wonder if a dusting of bentonite would help that.  But it definitely is not a substitute for vermiculite as the OP asked about.  Maybe if fired it could be, if that stabilized it in an expanded form.

Adding bentonite in tiny amounts to some earth dirts may be beneficial, but I don't think it should be used in Mel's Mix, since it is perfect.

I feel that clay particles in a hot clime will stil dry out and prevent the plants taking up moisture.

In hot climes it seems that a good thich insulating mulch is one of the best ways of helping the soil retain moisture by slowing  down natural evaporation & insulating the root areas from excessive direct ground heat . This helps the plants to retain water instead of them going all out to perspire and try and keep themselves cool instead of being cooked alive where they grow.

Indeed a mulch is very beneficial yet that does not mean that a small amount of bentonite is not also beneficial.  1-3% for poor water holding sandy soils according to http://www.bentonitewa.com.au/index.php/bentonite-applications/bentonite-agriculture-horticulture
That corroborates the claim in the article I had earlier linked of helping moisture retention in sandy soils and containers.  And it gives an idea of the amount, 1-3% is very small.  That article suggests the reason why bentonite is preferable to other clays.  Its small particle size and lightness means it evenly distributes through a planting medium (like the beach sand that makes good castles, each sand grain has a thin coating of bentonite) and the very jelly way it becomes when full of water is easy for plant roots.  Those properties would also be why it is good as a dusting on plants to protect from excess sun and insect protection (I had read trials at UCDavis diatomaceousus earth for this, but bentonite would be much cheaper).

However when all is said and done bentonites main use in agriculture seems as a medium for holding and distributing chemicals for pesticides and fertilizers.  It is also the medium for rhizobial legume inoculant.

And to get back to the OP's question. No, it is not a cheap substitution for vermiculite.  

Probably one of the useful ways that Bentonite Clay can help in the garden is for moisture retention in sandy soils. When added to sandy soil, this light clay swells up, almost jelly-like and stops the soil from drying out. Unlike heavy clays, bentonite doesn't form lumps so plants roots have no trouble obtaining moisture from their surroundings. Excellent for adding to soils in container plants. - See more at: http://www.no-dig-vegetablegarden.com/organic-garden-fertilizers.html#sthash.4l7N2Kqf.dpuf

Very informative posts.  I learned a lot reading through them.  Thank you for sharing.