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Organic Phosphorus Fertilizer - What is it and how do you make it?

April 19, 2021 5 min read

What is Phosphorus and how do you make it at home?

Most phosphorus is derived from mined rock. However, another natural source of phosphorus for plants is animal bone. The recipe will explain how to turn ordinary animal bone into dry bone meal phosphorus fertilizer.

Phosphate miningMost of the world's phosphorus comes from phosphate rock mined at sites like this in Nauru, Micronesia. This is because inorganic rock phosphorus is much more abundant than organic sources of phosphorous in animal and plant tissue. There is also no known way of synthesizing phosphorus.     Lorrie Graham,_2007._Photo-_Lorrie_Graham_(10729889683).jpg

What is in fertilizers?

All plant fertilizers contain nitrogen, phosphorus, and potassium. These are the macronutrients, the elements found in the largest quantities in plants. Different types of fertilizer contain these macronutrients in different amounts and ratios.

Nitrogen (N) is critical in chlorophyll and amino acid building. It aids leaf production. A nitrogen deficient plant will send the nutrient to young shoots first and then to mature leaves. Dying mature leaves can be a sign that your plant needs nitrogen. 

Phosphorus (P) is involved in energy transfers for cell metabolism. It comprises the structure of cell membranes and nucleic acids. Stunting, purple leaves, and lesions are signs of deficiency.

Potassium (K) regulates stomata (small pores on the leaves that allow gases to move in and out of plant cells), maintains turgor (water pressure in the plant that keeps it upright), and osmotic equilibrium (the transfer of nutrients in the plant from areas of high to low density). Leaf lesions are a sign of potassium deficiency, with mature leaves dying first. Potassium is particularly crucial in fruit growth.

While plants also require thirteen other elements in smaller quantities, these micronutrients are usually found in sufficient quantities within the soil. Plants need all three macronutrients and thirteen micronutrients to carry out essential physiological maintenance and achieve growth.

How do plants eat?

Daniel Öberg

All nutrients are taken up from the soil by the root and transported through the plant.

Nutrients are moved through the plant through three mechanisms:  transpiration, root pressure that pushes water and nutrient ions upwards, and the source-sink phenomenon, which draws water and ions from less active parts of the plant to places that are actively growing, such as shoots or fruit.

What are phosphorus-rich fertilizers?

Phosphorus-rich fertilizers contain a higher ratio of phosphorus compared to the two other macronutrients (nitrogen and potassium). You can identify commercial brands of phosphorus-rich fertiliser by looking for nutrient percentages like 15-30-15, which means that the macronutrient content is 15 % nitrogen, 30 % phosphorus, and 15 % potassium. 

The ratio figures you find on commercial fertilizer brands are called ‘NPK’ ratios. Each number indicates the percentage of nitrogen, phosphorus, and potassium respectively in the fertilizer. The rest of the product is filler material that does not impact the plant. 

A 5-5-5, 10-10-10, or 12-12-12 fertilizer contains nutrients in a 1:1:1 ratio to one another. All three of these NPK ratios indicate a balanced fertilizer, containing equal amounts of each macronutrient. The only difference between a 12-12-12 fertilizer and a 5-5-5 fertilizer would be that you need to use less of a 12-12-12 product than a 5-5-5 product since the first contains 7 percent more nitrogen, phosphorus, and potassium. 

Fertilizers with lower macronutrient percentage figures should be used on smaller plants and those with higher macronutrient percentage figures should be used on larger ones.

Homemade, organic fertilizer recipes tend to contain less concentrated amounts of the target nutrients than commercial, chemically synthesized ones. This lessens the chance of killing plants with over-fertilizing. It is also more environmentally sound, as there is less chance of releasing excess fertilizer into the wild.

When to use phosphorus fertilizer


Every plant needs some phosphorus to carry out essential physiological functions. However, fertilizers with a higher proportion of phosphorus compared to other macronutrients specifically aid the production and maintenance of flowers. It also promotes strong coloration in non-flowering foliage plants. 

High-phosphorus fertilizers should only be used just before and during the your plant's flowering season. Usually, the plants that like phosphorus fertilizers will also appreciate high levels of potassium. These include outdoor flowering plants like Dahlias and Verbenas, indoor flowering plants such as African violent, and many root vegetables like carrots and turnips. Hydrangea fertilized with phosphorus will produce pink rather than blue flowers. 

Signs of phosphorus deficiencies are purple streaks on the leaves or an overall purple appearance. In soils with a pH level below 6 and above 7, phosphorus forms in compounds that are difficult for your plant to use. If your soil is very alkaline or very acidic, you may need to modify it to prevent phosphorus deficiency. 

Be wary of over-fertilizing with phosphorus. Unless a soil is extremely deficient in phosphorus, or it contains none at all, a flowering plant should still be able to bloom. Toomuch phosphorus can lead to iron and zinc deficiencies as well as excess salts in the soil. Usually, the soil in your potted houseplant will contain sufficient amounts of phosphorus so there will be no need to add high-phosphorus fertilizer. Phosphorus deficiencies in the soil are more common in intensively farmed tracts of agricultural land than non-agricultural soils, unless it is a quite sandy soil. You can do a soil test if you are unsure of the nutrient levels in your soil.

How to make phosphorus for plants: Homemade phosphorus fertilizer recipe

Phosphorus is probably the hardest of the three plant macronutrients to make at home. 70-80 % of phosphorus in cultivated soils globally are derived from mined phosphate rock. However, phosphorus also exists in bone tissue. Below is a recipe for bone meal phosphorus fertilizer - an organic phosphorus source that will save you a trip to your nearest phosphate mine.

Recipe for homemade phosphorus fertilizer

cooking bones

Natalia Bazilenco

Save a heap of animal bones from cooking or source cast-off bones from your local butchers. Store them in the freezer as you collect them. 

Once you've saved enough bones for your fertilizer needs, boil them and scrape as much remaining fat and meat off manually. 

Sterilize the bones by baking them in the oven at 400-450°F until they become very dry and brittle. This will take an hour for small bones and more if the bones are large.

Place the bones into a bag and smash with a mallet or bat so the bones become fragmented. Fragment the bones as finely as you can.

Put the bone fragments into a blender and grind until they are fine. 
You can scatter the bone dust on your soil to boost phosphorus levels. You can add this bone meal to other organic fertilizer recipes to provide the phosphorus component. 

If you would like to experiment with your own organic fertilizer recipes, Oregon State University has compiled a useful table showing average NPK ratios in various organic substances. You can use it to figure out which ingredients you need to create a perfect NPK ratio mixture for your plant.   

Homemade Phosphorus too much work? You can buy from our favorite sources below. (as an Amazon associate we earn from qualifying purchases)


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