Down To Earth Rock Phosphate All Natural 0-3-0 OMRI 5lbSoft rock phosphate, or colloidal phosphate, is a natural, untreated, vegetarian source of long-lasting phosphate and soil building calcium. Rock phosphate provides phosphate that remains available to plants across a wide pH range. For best availability, Down To Earth’s soft rock phosphate should be mixed into soil or active compost prior to planting. A superb nutrient resource for plants of all kinds.