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Soft Rock Phosphate

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Soft Rock Phosphate Also Known As Colloidal Phosphate

Soft Rock Phosphate

Colloidal phosphate, is one of the best source of natural phosphorus and calcium known.

Being a completely natural source of phosphate it is OMRI listed and can be applied without restriction in any certified organic operation.

The Organic Materials Review Institute (OMRI) provides organic certifiers, growers, manufacturers, and suppliers an independent review of products intended for use in certified organic production.

For the gardener, buying any product that has this  Photo of OMRI-listed-logo logo on the label is an indication that the ingredients within the product comply with the USDA’s National Organic Program (NOP)

It is a by-product of the hard rock phosphate mining industry. Colloidal clay lies between the various layers of hard rock phosphate, in order to increase the purity of the hard rock phosphate. This colloidal clay is washed off during the mining process and accumulated in settling ponds. Once the surface has dried out the soft rock phosphate is skimmed off the top of the settling pond.

Soft rock provides benefits to plant life by encouraging growth of soil bacteria and earthworms and unlike many other nutrients it remaining in the soil until used by the plants without leaching. It also contains calcium, iron, boron and a good supplier of silicon. It is good to add to the compost heap and a great addition, along with other soluble nutrients, as a liquid fertilizer.

Like hard rock phosphate soft rock is not a complete fertilizer and is usually used along with other nutrient sources to create a custom fertilizer.


Photo of granulated soft-rock phosphate

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Soft rock can be purchased in granular form making it easy to apply.

Photo of soft rock phosphate powder

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In its original form it is a fine grade powder material. Much of the phosphate is immediately available to plants with the remainder being made available over a longer period of time.

Use at all stages of growth, can be plowed under or tilled into the soil prior to planting or used as a topdressing at 5 lb 100 sq.ft.

1/4 to 1/2 cup per plant

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