Greenway Biotech Gypsum Powder, Calcium Sulfate, 50 lb Review

Our Verdict

Gypsum has a real, narrow, well-documented use: displacing sodium from the exchange sites of a clay soil so irrigation can carry it below the root zone. Clemson's rate for that job is 50 pounds of granular gypsum per 1,000 square feet monthly, which makes this 50 lb bag exactly one application, and the guaranteed analysis here (22.5% calcium, 18% sulfur) is in line with what extension literature describes for calcium sulfate. It does not change soil pH, which is what separates it from lime and why it is the correct choice after saltwater flooding rather than a liming product. Now the part that decides whether you should buy it at all: Clemson states plainly that gypsum is not recommended for sandy soils with low sodium levels. That covers most of the Florida and Gulf Coast lawns that saltwater actually reaches, where the fix is fresh water and time rather than a bag of anything. Gypsum is also widely sold as a general clay-loosening conditioner, and that broader claim is far weaker than the sodium one. Buy this if a soil test shows sodium on a clay soil. If you have not tested, you are guessing at a chemistry problem, and this is the one purchase on the site where we would rather you spent the money on the test first. Practical note: it is a water-soluble powder rather than a pellet, which moves into the profile fast but blows in wind — spread it on a still day.