You may have heard of using gypsum in construction (for wallboard), but you can also use gypsum in your garden as a soil additive. That raises the questions of why you might want to add gypsum to your soil and when you might want to do it.
So, what is gypsum used for in soil? Gypsum is added to soil to supplement calcium and sulfur without changing soil pH. Gypsum can also remove excess sodium from sodic (saline) soils and break up compacted soil.
Gypsum is often used to replace calcium in soil used for large-scale industrial farming. However, you might still want to add gypsum to your soil in certain situations.
Let’s take a closer look at what gypsum is used for in soil. Then, we’ll answer some commonly asked questions about gypsum.
What Is Gypsum Used For In Soil?
Gypsum has several important applications when added to soil for gardening and agriculture. So what are the benefits of gypsum? Let’s take them one at a time.
Gypsum Adds Calcium and Sulfur to Soil
You can add gypsum to your soil to provide calcium and sulfur. Both of these nutrients are necessary for proper plant growth.
These nutrients will remain available to plants for weeks or even months after the addition of gypsum to your soil.
An added benefit is that adding gypsum to soil does not change the soil pH. This is useful if your soil pH is in the proper range, but you have a deficiency of calcium or lime.
Of course, the only way to know for sure if you have a nutrient deficiency is to do a soil test. For more information, check out my article on how to do a soil test.
Gypsum Removes Excess Sodium from Soil
Gypsum also helps to remove excessive sodium from soil. So why is this helpful?
First of all, too much sodium in soil reduces the amount of water available to plants. This will slow plant growth, and it will happen even if the soil has plenty of moisture.
In addition, excessive sodium can enter plants by transpiration and injure leaf cells. This will also slow the growth of plants.
For more information, check out this article on soil salinity from the University of Georgia Extension.
If you live near the coast by an ocean or sea, it may be helpful to use gypsum to remove excess sodium from the soil.
Gypsum Breaks Up Compacted Soils
Gypsum also helps to break up compacted soil. Soil often becomes compacted by foot traffic or heavy flooding. Clay soil also tends to be compact, and can benefit from some gypsum.
When your soil is compacted, it is able to hold less water and air. This makes it more difficult for your plants to grow and survive.
Of course, you can also use a rototiller to break up compacted soil. For more information, check out my article on rototilling.
If you do not want to disturb your garden and the worms that live there with a rototiller, you can add compost or manure to your garden instead. Just make sure that manure is fully decomposed before adding it to your garden!
Gypsum Counters Aluminum Toxicity
One final benefit of gypsum is that it will reverse aluminum toxicity in your soil. As usual, a soil test is really the only way to tell if you have this problem in your garden.
What Is Gypsum?
Gypsum is calcium sulfate, which means that it contains calcium, sulfur, and oxygen. It is used in gardening and farming for the purpose outlined above.
Gypsum is also used in other industries, such as construction (gypsum wallboard) and art (plaster).
For more information, check out this article on gypsum from Wikipedia.
How Does Gypsum Affect Soil pH?
Gypsum does not affect soil pH. That is, adding gypsum to soil will neither raise nor lower pH. As mentioned earlier, this makes gypsum a useful additive to supply calcium or sulfur if the soil pH is already in the correct range.
Calcium does displace hydrogen ions in soil. However, these ions are still dissolved and so the pH is unaffected.
For more information, check out this article on gypsum from the Michigan State University Extension.
On the other hand, lime (or calcium carbonate) does affect soil pH. In fact, there are several differences between gypsum and lime.
Are Gypsum and Lime the Same Thing?
No – gypsum and lime are not the same thing. Gypsum is calcium sulfate, while lime is calcium carbonate.
Both gypsum and lime contain calcium. However, the similarities end there.
Gypsum contains sulfur, while lime does not. Instead, lime contains carbonate, which is made of carbon and oxygen.
According to the Iowa State University Extension, refined gypsum has 29.4% calcium and 23.5% sulfur by weight. On the other hand, lime has 40% calcium and 12% carbon by weight.
When added to soil, gypsum leaves soil pH unaffected. Lime raises the pH of soil (the carbonate reacts with hydrogen ions).
Finally, gypsum adds calcium to soil more rapidly than lime, since gypsum is more soluble than lime.
If you are using gypsum as a sulfur supplement, it is worth noting that there are other sulfur sources you can use. For example, ammonium sulfate is more soluble than gypsum, and also adds nitrogen in a form that plants can use.
To summarize, here is a table comparing gypsum and lime side-by-side.
|Effect on Soil pH||none||raises pH|
Can You Use Lime and Gypsum Together?
Yes, you can use lime and gypsum together. The effect will be that you add both calcium and sulfur to your soil while raising pH. The more gypsum you use to replace lime, the smaller the pH increase will be.
Keep in mind that both lime and gypsum contain calcium. This means that you run the risk of adding too much calcium to your soil if you overdo it with either of these compounds.
Excessive calcium in soil can prevent plants from absorbing magnesium, even if there is plenty of magnesium in the soil. As usual, do a soil test to find out if you should add calcium compounds (or something else) to your soil.
Is Gypsum Harmful to Plants?
Gypsum may be harmful to plants if you add too much to the soil. As with anything, too much of a good thing can be a bad thing.
As mentioned earlier, applying too much gypsum can lead to excessive calcium in the soil, which in turn can prevent uptake of magnesium.
Moderation is the key, as is testing to make sure that your soil can handle the calcium and sulfur that gypsum will add.
Can Gypsum Be Used As Fertilizer?
Gypsum can be used as a partial fertilizer, but it is not a complete fertilizer. Gypsum provides calcium and sulfur to soil, but it does not contain any of the “big three” nutrients: nitrogen, phosphorus, and potassium (or NPK).
These three nutrients are essential for all plants. If your soil is lacking or if you are planting “heavy feeders”, then you may want to use an NPK fertilizer.
For more information, check out my article on NPK ratios.
There are other important plant nutrients, such as magnesium, that gypsum does not provide. You can use Epsom salt (magnesium sulfate) to provide magnesium, but remember to test your soil to make sure you don’t add too much!
Can You Apply Too Much Gypsum to Soil?
It is certainly possible to add too much gypsum to soil. You can end up with the problems mentioned above, such as excessive calcium and a resulting magnesium deficiency in plants.
Also, too much gypsum can cause leaching of iron and manganese (two other important plant nutrients) from the soil.
For more information, check out this article on gypsum from Washington State University.
If your soil is not deficient in calcium or sulfur, consider other supplements to help loosen compacted soil. For example, compost and manure can help to add organic material and improve drainage in compacted soil.
How Much Gypsum to Add to Soil
Get a soil test before you decide how much (if any) gypsum to add to your garden soil. When you send your soil sample to an agricultural extension office, include information about what you are trying to grow in your garden.
They will give you recommendations along with the results of the soil test. Remember that there is a nominal fee involved with soil testing, but it is worth the price to avoid a poor harvest after a season’s worth of hard work planting, weeding, and growing.
By now, you have a much better idea of what gypsum is used for in soil and when you might use it. You also know about the properties of gypsum, and some alternatives you can also use.
I hope you found this article helpful – if so, please share it with someone who can use the information. If you have any questions about using gypsum in your soil, please leave a comment below.