Organic Fertilizer for Root Growth - Phosphate Rock

Detail of phosphate fertilizer.

Phosphate rock is ideal for providing plants with the phosphate nutrients they need in order to grow strong root structures. As far as organic fertilizer is concerned, phosphate rock is generally always useful. Phosphates can be beneficial in any plant growth scenario, making their application possibilities widespread.


The main component of the phosphate rock is, of course, phosphate. Typically, phosphate rock found in nature contains approximately 20% phosphates by weight. However, when refined for use as fertilizer, that percentage jumps to at least 30% for primary phosphate groups like phosphorus pentoxide, and trace amounts of other phosphate materials. Almost 90% of the phosphate rock produced in the world ends up used as fertilizer.

The second component you often see in phosphate rock organic fertilizer is calcium carbonate. This provides the calcium in the fertilizer since there are no other components to phosphate rock fertilizer that contains elemental calcium. Together, these two compounds are responsible for delivering high amounts of phosphorus and calcium directly to the plant.


The main benefit of phosphate rock fertilizer is that it provides an impressive kick start of nutrients to plants. For that reason, it is best to use this fertilizer just before you start growing your plants. This is especially true for root growth, as strong roots need both phosphate and calcium in order to reach their full potential. The use of rock phosphate in direct contact with the plant's roots has been known to increase veggie yield, new growth, blooms, and bloom size. In addition, rock phosphate is only slightly water-soluble, meaning that it will not wash away with the rain. Rock phosphate will continue to fertilize your plants for years to come.


Rock phosphate can be bought at most garden supply stores or ordered online. It usually comes in a powder or dust form that can be easily sprinkled into your garden. The best method for application is to sprinkle a teaspoon or two of rock phosphate dust into your hole at the time of planting or transplanting. For large plots, use 2 to 5 pounds per 100 square feet.

TIP: To make liquid phosphate rock, pour 1 cup of the rock dust into a mesh bag or tied to cloth or cheesecloth. Suspend the bag in 1 gallon of water and allow the mixture to sit overnight. The next day, water your plants with the rock water or put it into a sprayer and mist the plant's foliage. Not only does this give the plant an extra kick of nutrients, but bugs seem to find the smell unattractive.

In alkaline soils, though the phosphate may be present, it is not available for the plants to use. The reaction of phosphate rock with acids makes the phosphate available. For this reason, if you know you have alkaline soil, water plants fertilized with rock phosphate with water mixed with apple cider vinegar. The acidic vinegar will make the rock phosphate available for use by your plants. Use 2 to 3 tablespoons of vinegar per gallon of water.

Environmental Concerns

There are no environmental concerns with the use of phosphate rock fertilizer. In fact, root growth in naturally-growing vegetation has been augmented by eroded phosphate nutrients from phosphate rock in several places around the world. It is one of the most widespread organic fertilizer products you are going to come across and one of the most environmentally friendly ones too.

Unfortunately, concerns have arisen over the mining of phosphate rock. Phosphate rock is a non-renewable resource and it is becoming rapidly depleted through mining by the fertilizer industry. The debate is ongoing over whether the phosphate reserves will last us for 400 years, or only 25. As scientific research continues, we should all stay up to date on the latest.

TIP: If you can't find soft rock phosphate in your nursery, bone meal makes a great substitute.