Greenway Biotech Gypsum is finely ground, mined calcium sulfate dihydrate (97% CaSO₄·2H₂O) with a guaranteed analysis of 22.5% calcium and 18% sulfur. Both nutrients arrive in the forms roots absorb, and because calcium sulfate is a neutral salt, soil pH stays where it is. That makes gypsum the right calcium choice when a soil test shows low calcium at a pH that lime would push too high, and the right sulfur choice when elemental sulfur would acidify.
Gypsum is also used to reclaim sodium-affected (sodic) soil: its calcium displaces sodium from the clay so irrigation can leach it below the root zone. Garden calcium starts at 1 lb per 100 sq ft, worked in before planting; the label's sodic-soil rate is 100–200 lb per 1,000 sq ft, applied only after a soil test confirms sodium and where the soil drains.
It will not loosen ordinary compacted clay, does not change pH, and is too slow-dissolving for foliar, drip, or hydroponic use. Fine powder, packaged in Madera, California, in seven sizes from 1 to 50 lb.
