How Much Gypsum is Needed to Amend Soil?
- Gypsum (CaSO4) is valuable for soils that have been exposed to or contain a high amount of sodium. Sodium accumulation can cause ponding, hard-drying soils that are difficult to work and binds soil particles so tightly that roots struggle to penetrate. Gypsum amendments act to soften hard soils and create a more porous soil that is easier to work with and permits freer drainage and plant growth.
- Some soils have a tendency to form a salty crust after a hard rainfall. If vegetable or other seedlings appear to be having difficulties penetrating this hard crust, spreading 5 pounds of gypsum per 100 square feet of soil surface can help eliminate the crust.
- New lawns being laid over soils with high clay concentrations can be amended with up to 300 pounds of gypsum per 1,000 square feet. The gypsum should be thoroughly worked and watered into the soil. Established lawns can be treated with 40 to 50 pounds of gypsum per 1,000 square feet.
- Gardens or fields can be amended with 20 pounds of gypsum per 100 square feet. Added gypsum must be tilled into the depth of persistent sodium accumulation. Sufficient rainfall or watering and drainage will also be required to effectively address the high sodium concentration. Gypsum may also be used around shrubs or trees. Apply 1 to 2 pounds around each shrub, 2 to 3 pounds around evergreens and up to 1 pound twice yearly around rose bushes. Water the area thoroughly after applying gypsum.
- Lime is sometimes used to amend salty soils. When gypsum is spread on the soil, rain or watering will dissolve and move it more quickly than lime. Within about three years, gypsum may show a positive effect on plants growing in an acidic clay subsoil. Gypsum is sparingly soluble, which makes it nearly impossible to over-apply. However, while lime does add calcium to the soil, it also alters the pH. So, although lime is an ideal amendment where the pH is too low, gypsum is suitable when the pH is already within an ideal range.