Minerals for Soil (cont)
By: Charlie Nardozzi
Apply in late spring or summer to lower pH of alkaline soils. The primary nutrient supplied is sulfur; longevity is 1 to 2 years. Sulfur is mined in the western U.S., but most is a by-product of oil refining.
Apply at planting time or during the growing season to supply magnesium and sulfate. It's fast-acting, but benefits last 1 or 2 growing seasons. Epsom salt is mined in Europe, but most that is available to gardeners is manufactured.
Apply in fall to raise pH of acidic soils that contain insufficient magnesium. Primary nutrients supplied are calcium and magnesium; longevity is 3 to 4 years. Dolomitic limestone is mined around the world.
Apply in fall or spring to supply calcium and sulfate, or to improve soils that contain excess sodium. Benefits last 1 to 2 years. Gypsum is mined primarily in the western U.S.
Pelletized Calcitic Limestone
Apply in fall to raise pH of acidic soils that contain adequate magnesium. The primary nutrient supplied is calcium; longevity is 3 to 4 years. Calcitic limestone is mined in many regions around the world.
Apply in spring or during growing season to supply potassium, sulfur, and magnesium. Fast-acting so benefits are short-term, 3 to 6 months. Sul-Po-Mag is mined in New Mexico.
Apply in fall to supply trace nutrients such as aluminum, boron, iron, manganese, silica, and many others. Very slow acting, but provides long-lasting benefits, 5 years or more. Rock dusts are mined in all regions of the U.S., typically as a by-product of other quarry activities.
Apply both hard- and soft-rock phosphate in fall to supply phosphorus, calcium, and trace nutrients. Benefits are long-lasting, to 5 years or more. Har phosphate is mined in many regions around the world. Mined in Florida, soft-rock phosphate also improves soil moisture retention.
Apply in fall or spring to supply potassium and many trace nutrients. Greensand also improves soil moisture retention. Greensand is very slow acting; benefits last up to 5 years. Greensand is mined in New Jersey from a geologic marine layer.
Photography by Sabin Gratz/NationalGardening.com and John Goodman