darci60(7 oklahoma)February 13, 2008

I have read on this forum and otherplaces that for our clay soil in tulsa it's good to use gypsum to break it down and make it useable. I really want to do this if it works as good as it sounds.

So where would I purchase gypsum? And is there a particular grade to use? I understand that it takes three years of application and that's ok . I just want to get the right thing.


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It is questionable whether gypsum would be of an help with you clay soil. It is useful for sodic soils where the Ca replaces the Na but for other clays soils, compost and lots of sand will help. In fact that will also help sodic soils.

Having said that, gypsum can be used to fertilize you soil with Ca without affecting the pH. The grade you want is agricultural gypsum. I purchase mine at the local gyprock seller.

Here is a link that might be useful: Sand

    Bookmark   February 13, 2008 at 1:04PM
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Belgianpup(Wa/Zone 7b)

One thing that would probably be of value to you is to call your most-local Cooperative Extension Service and ask them where you could get a soil test done. Here in WA, a soil test costs about $8. Tell them that you want the info for vegetable gardening.

They should send you written results, telling you if the levels are high or low or okay, and if something needs tweaking, they usually tell you what to use. If you need more info, they usually have a phone number to call.

Your Cooperative Extension Service is a wealth of information, and they love to pass on their knowledge, from best varieties for your area, weather and frost dates, how to solve certain problems. If you live near their office, they often have a bunch of free pamphlets on all kinds of things.


Here is a link that might be useful: Oklahoma Co-op Ext Service offices

    Bookmark   February 13, 2008 at 3:05PM
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albert_135(Sunset 2 or 3)

Dr. Chalker-Scott's The Myth of Gypsum Magic says:

The Bottom Line
Gypsum can improve heavy clay soil structure and remove sodium from saline soils
 Gypsum has no effect on soil fertility, structure, or pH of any other soil type
 Most urban soils are not improved by additional gypsum
 Before adding gypsum or any chemical to a landscape, have soil analysis performed to identify
mineral deficiencies, toxicities, and soil character
 Adding gypsum to sandy or non-sodic soils is a waste of money, natural resources, and can have
negative impacts on plant, soil, and ecosystem health

    Bookmark   February 13, 2008 at 4:19PM
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Albert 135


I find the easiest gypsum to work with is what's sold at home depot, and it's pelletized gypsum: it goes through the spreader quite nicely. Or if you're putting it in a flower bed/garden setting, the pellets (just like fertilizer) are easy to handle.

    Bookmark   February 13, 2008 at 5:19PM
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Lots of western soils benefit by the addition of gypsum. As noted above, gypsum helps with heavy clay soils with sodic content. You probably don't even need a soil test to find out if your clay soil is sodic; just ask the extention service folks. I looked at one of my books which shows most of Oklahoma red clay as impacted by caliche, so you are almost certain to benefit from gypsum application. My experience using gypsum has been very positive. It not only helped to improve the top soil structure, but also did quite a bit to improve the subsoil caliche layer that is common to many of our western soils. I found that I had much better drainage, that the caliche layer had noticably better penetration by roots, and that plants with deep roots had much more success penetrating below our caliche layer which in spots is less than a foot below the surface. Gypsum is quite cheap, easy to apply, and shows marked improvement in the soil in a year or so for me. I find that our only wet time (winter) is a great time to apply it so that it begins the migration into the soil. Lots of the hardware stores around here carry it. Since application rates recommended tend to be fairly high, I find it good to shop for the best price, even though the stuff is fairly cheap to begin with. I agree that the pelleted material is much nicer to work with, particularly if the day is windy, but it is also quite a bit more expensive here. If you pick a calm day for application, then the standard material, which is like a white sand, works well also.

    Bookmark   February 13, 2008 at 8:28PM
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If you have a sodic clay soil gypsum may help eliminate some of the sodium from that soil. I am not aware that Oklahoma has any sodic clay soils, so what you need to improve your soil is lots of organic matter.

    Bookmark   February 16, 2008 at 8:27AM
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I came here to ask this question about Kentucky's clay soil. I read in "The Well-tended Perennial Garden" that gypsum works on some clay soils in the western part of the country but has no positive effects east of the Mississippi. Anyone have a conflicting experience with gypsum?

    Bookmark   November 26, 2008 at 7:53AM
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greenwood, because of the normal amount of rain Kentucky gets the clay soils would not have large amounts of sodium that gypsum would aid in removing, so adding gypsum to your soil will really be of little benefit unless a good, reliable soil test said there might be a reason to use that in place of clacitic or dolomitic lime.

    Bookmark   November 26, 2008 at 12:26PM
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I read Soil Conditioner and Amendment Technologies Volume 1995 by A. Wallace this summer and was impressed by the value of gypsum as an all purpose soil conditioner and a readily available source of Ca and S. The book is a bit pricey so get it through inter-library loan.

Item 126 in the PDF file below lists all the benefits of gypsum. These benefits are fleshed much more in the book.

Volume 2, 1997 is previewed in Google Books.

    Bookmark   November 26, 2008 at 8:58PM
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Hey, folks - get back to basics and get your facts straight.
Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O
Mined from huge deposits below ground in many places, worldwide.
A common use of gypsum is building products such as 'gypsum wallboard' or 'drywall'.

What is this 'fixation' on sodium (sodic) relative to clay?
Sodium is not the issue that darci60 asked for help with.
Sodic: Relating to or containing sodium (NA).
So most soils are 'sodic' in nature, simply because they contain sodium.
So does coca-cola and a huge number of other products.

But the word missing from responses about this topic is: FLOCCULATION.
Flocculation refers to the process by which fine particulates are caused to CLUMP TOGETHER into floc.
That's what darci60 is asking about - ...'breaking it down' - which has almost nothing to do with sodium content.
That's the MAIN thing gypsum does to clay soil - cause it to 'clump' - to become more 'manageable' for plant roots.
Clay is the smallest particle size per USDA soil classification. Toughest for plants to grow in.
Clay soils are problematic - due to that tiny particle size and therefore, poor cation (ion) exchange.
Neutralization of sodium (and other mineral salts) is simply an added benefit.

Gypsum particles (crystals) qualify as silt (grain size between clay and sand).
And yes, organics are certainly highly beneficial in any soil, but does not do what gypsum does - as fast.
In fact, organics (such as compost) is usually high in mineral salts and can benefit from gypsum application too.
I use gypsum regularly in the compost I make - and to make soils such as loam.
Secondly, gypsum (as calcium sulfate) is NOT a fertilizer per se. Usually 23% and Sulfur 16.5%
Thirdly, if you add just sand to clay - you just made a material very similar to cement. Not smart.
The sulfur content CAN help adjust pH of alkaline soils downward.

Pelletized gypsum is recommended for artifically-made soils or potting media. Not flocculating clay.
Gypsum does not care where it is applied, and 'east of the Mississipi' is irrelevant.
The recommendation to check with your local Coop.Ext. office is a good one.
However, soil analysis will not help much, although highly recommended for other purposes.
Routine test = N,P,K - no help.
R+Micro = gives amount of CA and NA in the sample - but that's still not much help.
% organics - still not of much use - but adding more is always beneficial.
The best use of the Coop.Ext. service is their Master Gardener Association (volunteers).
Contrary to Dr. Chalker-Scott's, state soil analysis do NOT normally identify soil 'character'.
Secondly, adding gypsum to CLAY is beneficial (to break it up) regardless of sodic content.
And take serious exception to the statement: "...negative impacts on plant, soil, and ecosystem health".
Such broad/sweeping generalities are not helpful.
Plaudits to renais - with the exception of the sodic issue, you're right on target.
While sodium does leach in some soils - Sodium-bound ions do NOT leach from clay (research cation exchange).
Lime will adjust pH, but has no benefit with regard to flocculation or reducing sodium from soils.
cowgirl2 - you're 'right on' - very good information.

Darci60 - I live on hard, salty clay on the southern coast of Texas. Saltier than ocean water.
I'm familiar with your clay. My mom and dad lived in Tulsa and taught organic chemistry at O.R.U.
They amended with compost and gardened beautifully. But it took them years to do it.

That clay soil is tough to work with, but CAN be revitalized - over a period of time.
Not going to happen quickly. Gypsum can help, but focus on MICROBES. In organic matter.
If you're serious about gardening in Tulsa clay, learn how to compost seriously. You'll need tons.
Read up on micorrhizal fungus inocculation if you're already trying to grow plants in that stuff.
Install a drip irrigation system in the garden with only 2 gal/hr emitters.
Clay absorbs slowly, but stays wet - problem is, there's almost no air in clay due to particle size.
Pick a small area to begin with. Get that soil broken up first, as best you can. Then work outward, inch-by-inch.
Small tractor disc is best initially - but can be done with a strong garden fork. 1st time is tough, but water good, then wait for a day or two before tackling it. Much better after you get down about 6". Go for at least 12".
Then add gypsum pre-mixed into organic matter. Turn it under. Water sparingly. Preferrably use compost. But don't buy it. Make it free.
Trench your compost pad - put plastic over it - and collect leached compost 'tea'. Best tonic for clay soil.
Full of nutrition and microbes - but microbes won't thrive on just fertilizer. Organics needed.
Do NOT put wood shavings/sawdust (cellulose/lignin) down into that clay. Will deplete already-scarce nitrogen.
Wood belongs only on the soil surface - as mulch. But mowed grass clippings are BETTER to flocculate clay.
Get a bagging lawnmower and use it to shred leaves, too.
Garden with raised beds. Flowers too. Get their roots up out of soggy, anaerobic (poorly draining) clay.
Research online - visit your local Master Gardener group and ask lots of questions (I'm a certified Texas Master Gardener and have been composting 50+ years) - read books in the library.
Visit places near you that have successfully 'beat the clay' and learn how they did it.
Good luck.

    Bookmark   November 26, 2008 at 11:15PM
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I read some materials from the Utah State University cooperative extension years ago and they said that gypsum isn't usually helpful for the clay we have in Utah. I couldn't remember the details so I did a search on it.

The results I found said that gypsum is helpful to sodic clay. The first result talks about areas of sodic soil in Utah, but in general, the clay we have here tends to be high in calcium, so adding gypsum doesn't help much. The reason gypsum can help with sodic soils is that it releases the sodium so it can be more readily leached out. For a similar reason, it can also help with certain saline soils.

Gyspum will usually not affect the pH very much. In fact, that is sometimes used as a "selling point" because it can be used to add sulfur to acidic soils that are low in sulfur without lowering the pH (unlike adding soil sulfur) and it can be used to add calcium to alkaline soils without raising the pH (unlike lime).

I didn't thoroughly read all the information I found this evening, but just scanned it and summarized some of the points.

If you want to read the details, click here and follow some of the links.

I would agree with the comments that the best way to find out if gypsum will help in your area is to check with your extension office. The search I did is limited to the USU extension. In Utah, gypsum would only be helpful in certain areas and is not helpful in others. If you have caliche or other calcic soils, adding gypsum isn't likely to be very helpful.

    Bookmark   November 27, 2008 at 12:02AM
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As a rule gypsum costs money, you have to buy it. As a rule organic matter is pretty readily available for free, excpet maybe the cost of transportation which also must be figured into the cost of the gypsum. So "free" always beats "spend money", and the organic matter will do much more to improve that clay soil than several hundred pounds of gypsum.

    Bookmark   November 27, 2008 at 8:14AM
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