Gypsum – Used to Prevent Blossom End Rot

Q: We grow tomatoes in a little raised bed and have always used garden lime in the past. I keep hearing about using gypsum (calcium sulfate) for calcium, but I worry that it will increase soil acidity.

A: Gypsum is actually a neutral salt and therefore has little effect on soil pH. Since regular applications of lime might raise pH more than needed, I advise powdering a two inch by two inch piece of gypsum wallboard (Sheetrock, etc) and mixing with the soil to prevent blossom end rot on tomatoes.

Chemistry of Gypsum