Calphos Soft Rock Phosphate - Regular Powder (50 lb)

Calphos Soft Rock Phosphate is a finely ground mineral amendment that supplies phosphorus and calcium gradually. This original 50 lb package is the primary choice for larger gardens, orchards, farms, and multi-bed soil-building projects. It is OMRI listed and CDFA approved for use in certified organic production.

What it supplies

Calphos averages approximately 20% P₂O₅, including 3% available phosphate, and about 18% calcium. Phosphorus supports energy transfer, root establishment, flowering, and fruiting when soil levels are deficient. Because phosphorus moves slowly through most soils, Calphos is best incorporated where developing roots can access it.

Best uses

• Preparing vegetable beds and field rows before planting
• Amending orchard and perennial planting areas
• Blending with compost or other soil amendments
• Correcting low phosphorus identified by a soil test

More phosphorus is not always better. Excessive applications can create nutrient imbalances and increase environmental risk, so begin with a current soil test and follow crop- and region-specific recommendations.

Application guidance

• Garden beds: The general published rate for phosphorus-deficient soil is 5 lb per 100 sq ft; use less in more fertile soil.
• Field applications: Published guidance is up to 1 ton per acre on deficient soils.
• Trees and perennials: Published planting-hole guidance ranges from 1–10 lb depending on plant size.
• Placement: Mix evenly into the soil or compost before planting rather than leaving the amendment concentrated on the surface.

Choose the right package

This 50 lb original package carries the product’s OMRI and CDFA organic-use status. For smaller projects, see the 5 lb bag or 25 lb bag. Those repackaged sizes are not represented as organic, and the certification status of this package does not transfer to them.

For more planning guidance, read How to Use Fertilizers: Soft Rock Phosphate, browse high-phosphorus fertilizers, or explore all fertilizers and growing supplies.

Compare this product with additional nutrient-specific fertilizers selected for garden and farm fertility programs.