The Myth of Gypsum Magic

[BrnCow]

Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University

The Myth of Gypsum Magic
“Adding gypsum to your yard or garden will improve soil tilth and plant health”

The Myth

Upon continued prodding from one of my university extension colleagues, I recently watched several
episodes of a well-known gardening program on television. My kids joined me, alerted by my animated
responses to the host’s non-stop torrent of advice. Among many amazing discoveries I learned that by
adding gypsum to my yard or garden I would improve my problem soils by changing the particle size and
loosening compaction. Further searching on the web revealed that gypsum would also improve drainage,
decrease acidity, and eliminate soil salts. Previously, I had heard of gypsum for use in soil reclamation
projects, but not for a typical urban landscape. Since gypsum is simply calcium sulfate, could this
chemical truly transform soil structure and serve as a fertilizer for yards and gardens?

The Reality

This myth falls into the category of agricultural practices misapplied to ornamental landscapes.
Gypsum effectively changes the structure and fertility of heavy clay soils, especially those that are heavily
weathered or subject to intensive crop production. Gypsum also improves sodic (saline) soils by
removing sodium from the soil and replacing it with calcium. Therefore, one can see improvement in
clay soil structure and fertility, and desalinization of sodium-rich soils, by using gypsum.

What other effects will gypsum have on soil and plant health? There are a number of scientific studies
on gypsum usage both in the literature and on websites. Briefly, researchers have found:

• Gypsum does not usually change soil acidity, though occasional reports of both increasing and
decreasing pH exist;
• Gypsum can increase leaching of aluminum, which can detoxify soils but also contaminates
nearby watersheds;
• Gypsum can increase leaching of iron and manganese, leading to deficiencies of these nutrients;
• Gypsum applied to acid soils can induce magnesium deficiency in plants on site;
• Gypsum applied to sandy soils can depress phosphorus, copper and zinc transport;
• Gypsum can have negative effects on mycorrhizal inoculation of roots, which may account for
several reports of negative effects of gypsum on tree seedling establishment and survival;
• Gypsum is variable in its effects on mature trees;
• Gypsum will not improve fertility of acid or sandy soils;
• Gypsum will not improve water holding capacity of sandy soils; and
• Gypsum’s effects are short-lived (often a matter of months)

With the exception of arid and coastal regions (where soil salts are high) and the southeastern United
States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural
areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and – in home
landscapes – high levels of organic and non-organic chemical additives. They are also heavily compacted
and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add
yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient
deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If
you need to improve sulfur nutrition, it’s wiser to use ammonium sulfate). To reduce compaction and
improve aeration in nearly any landscape, application of an organic mulch is more economically and
environmentally sustainable.

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

For more information, please visit Dr. Chalker-Scott’s web page at http://www.theinformedgardener.com.

 

[supermanlives]

thanks . good read

 

[dekab247]

agreed...

agreed...

Good read, and thank you for the link...D

 

[Jamorg13]

Great find. WSU has a lot of great agricultural information

 

[wilbur]

yes, this IS good ... and succinct too. needs to be a Sticky!

I have some ancient granite river bed soil. need to use lots of gypsum ONLY to leach out excess magnesium salts.

I 've seen contributors to these forums advise the use of gypsum, even in pots, and I never believed them.

cheers!

 

[travis1565]

IcMag saves me money once more.

IcMag saves me money once more.

I was going to order up some gypsum as a soil amend for calcium and it ph potential. MNot after reading this thread. Yhanks once again I dont have much money so the more i keep the better.

 

[Slipnot]

Even though many studies have shown that there is no perfect ratio for cations, some people insist on trying to change the ratio of cations held on the soil with products like gypsum (calcium sulfate).

AGVISE recently conducted a laboratory project looking at the affect gypsum has on soil test levels of calcium, soluble salts, cation ratios, soil pH and CEC. The results of the laboratory project are shown in figures 2 & 3. Some people who sell gypsum claim that it lowers the soil pH dramatically. It is apparent that this is not true, even at rates as high as 36000 lb/a gypsum the soil pH is about the same as the check.

As the rate of gypsum is increased you can see the test level for calcium increases while the level of magnesium, potassium and sodium remain the same (Figure 2). [​IMG] When gypsum (calcium sulfate) is applied to the soil, it dissolves in the soil solution. Some of the calcium becomes attached to soil particles as part of the cation exchange capacity of the soil. The remaining gypsum stays in the soil solution as dissolved calcium sulfate salt. The soil testing method used by all commercial and University soil testing laboratories picks up the calcium that is held on the soil, as well as the calcium that is dissolved in the soil solution as soluble salts. The calcium in the soil solution is “NOT” held on the soil, and should not be included because it is not held on the soil, but it is included in the common method used by all soil testing laboratories. Because this soil testing method includes the calcium from the soil solution, the test values reported are inflated on the high side. You can see this inflation occurring as the rate of gypsum increases in Figure 2. The calcium test value goes up, but the soil is not holding more calcium, the test is just including the calcium dissolved in the salts in the soil solution. You can see this is true because the salt level increases as the rate of gypsum increases.

The base saturation value for a soil is a calculation that determines the percent each cation makes up of the total cations in the soil. When the percent base saturation for a soil is calculated, the ppm value for calcium, magnesium, potassium and sodium are used in the calculation. Since the calcium ppm level keeps increasing as more gypsum is applied, calcium becomes a larger percentage of the total cations. We know that the soil is not holding more calcium, we are just measuring the increasing amount of calcium in the salts of the soil solution.

The Cation Exchange Capacity (CEC) of a soil is the ability of a soil to hold the cations calcium, magnesium, potassium and sodium. The CEC of a soil is a permanent feature based primarily on soil texture, clay content and organic matter. When gypsum is applied to the soil it does not actually change the CEC of the soil, but it does change the calcium test value determined in the laboratory, which is used to calculate the CEC value for the soil. Because an inflated calcium value is used to calculate the CEC of the soil, the calculated CEC goes up as the gypsum rate increases (Figure 3). [​IMG] These CEC values are erroneous due to the error caused by including calcium from the salts in the soil solution. The correct CEC of this soil, determined by a special laboratory method that does not include calcium from the salts in the soil solution is 18 meq. The routine method, used by all commercial soil testing labs, did a good job of determining the CEC to be 17, until higher rates of gypsum were applied. That means that you can change the calculated CEC of the soil by adding gypsum, but you are not really changing the ability of the soil to hold cations.

Facts learned from past field research and AGVISE laboratory project:
You can achieve high yields on soils with a wide range of cation ratios.
You can apply enough gypsum to a soil to change the laboratory test results for calcium, but this does not actually change the CEC of the soil or the amount of each cations actually held on the soil.
Even low rates of gypsum over the long term on a poorly drained soil will increase the salt level of the soil. As the soil salt level increases, crop yields will decrease over time.
Gypsum does not decrease or increase the soil pH of productive soils
It is most important to know the level of each nutrient in the soil. If a nutrient tests in the deficient range, it needs to be applied. The concept of balancing cations is not supported by the facts of the real world.
Remember the number 1 killer for plants is salts have a nice day folks think of it as a magic amendment ,, if you like if you think its doing you better then by all mean use it
at the end of the day appears that you can grow nice healthy plants with out it,, like mine fist picture salt buiild up its inevitable with gypsuim Cause god forbid sulfate is not a salt

 

[corky1968]

I was going to order up some gypsum as a soil amend for calcium and it ph potential. MNot after reading this thread. Yhanks once again I dont have much money so the more i keep the better.

Want to save some money. Find a demolition site and snag some drywall pieces.
Smash it all and grind it into fine powder and pass the powder thru a screen.
There you go cheap gypsum.

Don't smash the walls in your place to get gypsum if your renting or your landlord will freak on you.

BTW: In some places drywall is named sheetrock.

 

[iTarzan]

The original post is misguided. We as canabis growers are using gypsum for agriculture not ornamental yard and lawn landscaping. The myth of gypsum states gypsum agricultural practices are being misused for landscaping.

We are not landscapers were are farmers. Gypsum could be helpful to our goals of better weed.

 

[slownickel]

Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University

The Myth of Gypsum Magic
“Adding gypsum to your yard or garden will improve soil tilth and plant health”

The Myth

Upon continued prodding from one of my university extension colleagues, I recently watched several
episodes of a well-known gardening program on television. My kids joined me, alerted by my animated
responses to the host’s non-stop torrent of advice. Among many amazing discoveries I learned that by
adding gypsum to my yard or garden I would improve my problem soils by changing the particle size and
loosening compaction. Further searching on the web revealed that gypsum would also improve drainage,
decrease acidity, and eliminate soil salts. Previously, I had heard of gypsum for use in soil reclamation
projects, but not for a typical urban landscape. Since gypsum is simply calcium sulfate, could this
chemical truly transform soil structure and serve as a fertilizer for yards and gardens?

The Reality

This myth falls into the category of agricultural practices misapplied to ornamental landscapes.
Gypsum effectively changes the structure and fertility of heavy clay soils, especially those that are heavily
weathered or subject to intensive crop production. Gypsum also improves sodic (saline) soils by
removing sodium from the soil and replacing it with calcium. Therefore, one can see improvement in
clay soil structure and fertility, and desalinization of sodium-rich soils, by using gypsum.

What other effects will gypsum have on soil and plant health? There are a number of scientific studies
on gypsum usage both in the literature and on websites. Briefly, researchers have found:

• Gypsum does not usually change soil acidity, though occasional reports of both increasing and
decreasing pH exist;
• Gypsum can increase leaching of aluminum, which can detoxify soils but also contaminates
nearby watersheds;
• Gypsum can increase leaching of iron and manganese, leading to deficiencies of these nutrients;
• Gypsum applied to acid soils can induce magnesium deficiency in plants on site;
• Gypsum applied to sandy soils can depress phosphorus, copper and zinc transport;
• Gypsum can have negative effects on mycorrhizal inoculation of roots, which may account for
several reports of negative effects of gypsum on tree seedling establishment and survival;
• Gypsum is variable in its effects on mature trees;
• Gypsum will not improve fertility of acid or sandy soils;
• Gypsum will not improve water holding capacity of sandy soils; and
• Gypsum’s effects are short-lived (often a matter of months)

With the exception of arid and coastal regions (where soil salts are high) and the southeastern United
States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural
areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and – in home
landscapes – high levels of organic and non-organic chemical additives. They are also heavily compacted
and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add
yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient
deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If
you need to improve sulfur nutrition, it’s wiser to use ammonium sulfate). To reduce compaction and
improve aeration in nearly any landscape, application of an organic mulch is more economically and
environmentally sustainable.

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

For more information, please visit Dr. Chalker-Scott’s web page at http://www.theinformedgardener.com.

Gypsum does not leach metals guy. It precipitates them. Gypsum pushed Mg and Sodium out which is why pH often falls. No build ups occur with Calcium either. 2gr/liter soluble. Washington State Extension baloney.

 

[slownickel]

Want to save some money. Find a demolition site and snag some drywall pieces.
Smash it all and grind it into fine powder and pass the powder thru a screen.
There you go cheap gypsum.

Don't smash the walls in your place to get gypsum if your renting or your landlord will freak on you.

BTW: In some places drywall is named sheetrock.

NOOOOOOO.

 

[slownickel]

Even though many studies have shown that there is no perfect ratio for cations, some people insist on trying to change the ratio of cations held on the soil with products like gypsum (calcium sulfate).

AGVISE recently conducted a laboratory project looking at the affect gypsum has on soil test levels of calcium, soluble salts, cation ratios, soil pH and CEC. The results of the laboratory project are shown in figures 2 & 3. Some people who sell gypsum claim that it lowers the soil pH dramatically. It is apparent that this is not true, even at rates as high as 36000 lb/a gypsum the soil pH is about the same as the check.

As the rate of gypsum is increased you can see the test level for calcium increases while the level of magnesium, potassium and sodium remain the same (Figure 2). When gypsum (calcium sulfate) is applied to the soil, it dissolves in the soil solution. Some of the calcium becomes attached to soil particles as part of the cation exchange capacity of the soil. The remaining gypsum stays in the soil solution as dissolved calcium sulfate salt. The soil testing method used by all commercial and University soil testing laboratories picks up the calcium that is held on the soil, as well as the calcium that is dissolved in the soil solution as soluble salts. The calcium in the soil solution is “NOT” held on the soil, and should not be included because it is not held on the soil, but it is included in the common method used by all soil testing laboratories. Because this soil testing method includes the calcium from the soil solution, the test values reported are inflated on the high side. You can see this inflation occurring as the rate of gypsum increases in Figure 2. The calcium test value goes up, but the soil is not holding more calcium, the test is just including the calcium dissolved in the salts in the soil solution. You can see this is true because the salt level increases as the rate of gypsum increases.

The base saturation value for a soil is a calculation that determines the percent each cation makes up of the total cations in the soil. When the percent base saturation for a soil is calculated, the ppm value for calcium, magnesium, potassium and sodium are used in the calculation. Since the calcium ppm level keeps increasing as more gypsum is applied, calcium becomes a larger percentage of the total cations. We know that the soil is not holding more calcium, we are just measuring the increasing amount of calcium in the salts of the soil solution.

The Cation Exchange Capacity (CEC) of a soil is the ability of a soil to hold the cations calcium, magnesium, potassium and sodium. The CEC of a soil is a permanent feature based primarily on soil texture, clay content and organic matter. When gypsum is applied to the soil it does not actually change the CEC of the soil, but it does change the calcium test value determined in the laboratory, which is used to calculate the CEC value for the soil. Because an inflated calcium value is used to calculate the CEC of the soil, the calculated CEC goes up as the gypsum rate increases (Figure 3). [IMG] These CEC values are erroneous due to the error caused by including calcium from the salts in the soil solution. The correct CEC of this soil, determined by a special laboratory method that does not include calcium from the salts in the soil solution is 18 meq. The routine method, used by all commercial soil testing labs, did a good job of determining the CEC to be 17, until higher rates of gypsum were applied. That means that you can change the calculated CEC of the soil by adding gypsum, but you are not really changing the ability of the soil to hold cations.

Facts learned from past field research and AGVISE laboratory project:
You can achieve high yields on soils with a wide range of cation ratios.
You can apply enough gypsum to a soil to change the laboratory test results for calcium, but this does not actually change the CEC of the soil or the amount of each cations actually held on the soil.
Even low rates of gypsum over the long term on a poorly drained soil will increase the salt level of the soil. As the soil salt level increases, crop yields will decrease over time.
Gypsum does not decrease or increase the soil pH of productive soils
It is most important to know the level of each nutrient in the soil. If a nutrient tests in the deficient range, it needs to be applied. The concept of balancing cations is not supported by the facts of the real world.
Remember the number 1 killer for plants is salts :) have a nice day folks think of it as a magic amendment ,, if you like if you think its doing you better then by all mean use it
at the end of the day appears that you can grow nice healthy plants with out it,, like mine :) fist picture salt buiild up its inevitable with gypsuim Cause god forbid sulfate is not a salt
[/QUOTE]
I have many years of data, not sure what these guys are peddling. Gypsum pushes out sodium. Lotta bullshit out there.

 

[VenerableHippie]

yes, this IS good ... and succinct too. needs to be a Sticky!

I have some ancient granite river bed soil. need to use lots of gypsum ONLY to leach out excess magnesium salts.

I 've seen contributors to these forums advise the use of gypsum, even in pots, and I never believed them.

cheers!

I have ancient granite and high Mg too here on the east coast of Australia. Mg so high plants can't take it up. Thought my soil was unique. Interesting to see it looks like high Mg is a phenomenon of ancient granite soils.

 

[VenerableHippie]

I used lots of Gypsum to help flush Roundup-affected soil then stimulated growth with Fulvic Acid. Saved the plants.

 

[slownickel]

I have ancient granite and high Mg too here on the east coast of Australia. Mg so high plants can't take it up. Thought my soil was unique. Interesting to see it looks like high Mg is a phenomenon of ancient granite soils.

Magnesium can actually go toxic. Took me years to figure that one out. Over 30% of the bases, Mg starts getting toxic. Around 34% sugar cane died in Hawaii. Maui sugar cane syndrome. If you want a copy let me know.

 

[jahshaka]

Gypsum Is the single best addition to my gardens all thanks to the advise of @slownickel. All the haters can keep on talking but slow lives it and has helped thousands grow nutrient dense crops. The Calcium is king.

 

[Douglas.Curtis]

Ya know you can completely skip this debate and use an amazing water soluble calcium from KNF methods. Toasted shells, vinegar and time. Calcium is awesome, and instantly available calcium even more so.

 

[islandpreservation]

Carey reams who developed hi brix farming would start off with chicken manure, gypsum, lime, and rock phos. supplying a broad range of calciums. He also recomended continuing with more lime than gypsum.Seems it is one of those thing that can be good depending on the situation and isn't always needed on repeat

 

[Ca++]

I'm not really sure who wrote that. The opening about watching TV with her kids didn't sound like your typical science paper. Scanning for big words, I find sodic and watershed. Watershed is used wrongly. Sodic she thought to explain. Slow spotted a factual mistake.

She has the feel of a school science teacher. Though the core message is right.

 

[moose eater]

Biggest troubles I've had from excess gypsum have been,

1.) increased sulfur, sometimes to the point of off the charts (exaggeration to a degree, but high S), especially if using other sources of sulfur in my mixes, to include bokashi bran, etc. And some fertilizers already have a Sulfur punch onboard.

2.) The quality of organic or other amendments can vary greatly, so testing for the ph of the product before mixing it is important. I've used (I think it was Epsoma brand) gypsum and had it affect ph negatively, creating issues with too much acidic value in the subsequent testing. Down to Earth's gypsum that I last tested was more a neutral ph.

I still use gypsum to increase Ca, but I use it more sparingly.