Should You Use Gypsum for Soil?
If you have hard clay or noticeably salty soil, gypsum can make healthy growth much easier for your garden plants. Here's what you need to know.
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Have you been using soil amendments like compost to change your clay soil into something easier to manage? Another option is gypsum. Your soil pH needs to be near neutral or higher because gypsum will not change soil acidity. But if that’s the case and your soil is hard, sticky, slow draining or salty, gypsum should help.
And what if your soil is a mellow loam or sandy soil? Garden soil that’s easy to cultivate needs ongoing additions of compost, but it does not need gypsum.
What is Gypsum?
Gypsum is a mineral, mostly made up of calcium sulphate. It is sometimes surface-mined, and sometimes recovered when coal plant emissions are scrubbed. Mined gypsum also might contain contaminants like heavy metals.
Don’t confuse gypsum with lime, i.e. ground limestone containing calcium that raises soil pH. If your soil needs lime to make it less acidic, do that first, and then add gypsum once the soil pH is 5.8 or above.
Different Sources of Gypsum
Some retailers claim naturally mined gypsum is suitable for organic production. Others do not, acknowledging it’s manufactured product.
If you feel strongly about organic certification, look for the OMRI or Ecocert label on the bag of gypsum. Be aware: Some gypsum is mined in areas of heavy metals, so all mined gypsum is not the same.
How Does Gypsum Work in Soil?
Gypsum may seem like a miracle solution for soil, if what you need is a miracle. If your clay soil is high in sodium and the sodium has replaced other minerals, like magnesium or calcium, the soil will separate or disperse into fine particles that stick to your boots and tools. Luckily, gypsum makes soil less sticky.
How Do You Use Gypsum in Soil?
If your soil needs to be worked or cultivated, do that first before applying gypsum. Gypsum is often sold as a powder, but I’ve purchased it like a fertilizer as little granules or beads, also known as prills.
Powdered gypsum is very fine. Like powdered lime, it becomes airborne and can be dusty. When you spread it, the small floating particles get in your nose and bother your eyes.
Pellets or prills are easier to use and less dusty. Use a drop-spreader or scatter the gypsum by hand (wear gloves), distributing it evenly over the garden soil at the rate suggested on the package. Irrigation or rain water will dissolve the gypsum and disperse it into the soil.
Should You Use Gypsum in Every Soil?
You should definitely try gypsum if a soil test indicates your clay soil is at or near neutral in acidity with a high level of available sodium. If your clay soil has a white crust on the surface, assume you have extra sodium.
Gypsum is also helpful where dry clay soils are hard to work or crusty on top. If it’s difficult for seedlings to push through this hard crust in the spring, gypsum can help.
If you have other types of garden soil, you don’t need gypsum. I have absolutely no use for gypsum on my sandy soil. Most people with loam, silty or other types of non-clay soil may not have any reason to try gypsum, either.
Keep in mind that adding gypsum alone does not replace soil amendments that lift and soften the soil. I’m a firm believer in soil amending first, gypsum second.