If a soil test reveals that your soil is lacking phosphorus, then you are probably looking for a way to supplement this important nutrient in your garden. Luckily, there are many options for high-phosphorus fertilizers.
So, what fertilizer is high in phosphorus? Fertilizers that are high in phosphorus include mushroom compost, hair, rock phosphate, bone meal, burned cucumber skins, bat guano, fish meal, cottonseed meal, worm castings, blood meal, manure, and compost.
Of course, you can use a mixture of any of these sources of phosphorus, depending on what you have available. You can also use fertilizers formulated as bloom or blossom boosters, which will have high phosphorus content.
Let’s get into more detail about just how much phosphorus each of these fertilizers contains, and how long it takes them to release into the soil.
(You can also watch my YouTube video on this topic if you prefer!)
What Fertilizer Is High In Phosphorus?
Here is a table with some of the best fertilizers with high phosphorus content. You can find more detail about each type of fertilizer after the table.
Note the numbers given in the table are percentages by weight, and that N = Nitrogen, P = Phosphorus, and K = Potassium. (You can learn more about NPK nutrients on fertilizer labels in my article here).
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their nutrient content (nitrogen, phosphorus, and
potassium). The numbers in the table are
percentages of each nutrient by weight.
Hair may not be the first thing you think of when you are looking for fertilizer for your garden. However, hair is 26% phosphorus by weight, meaning that it has the most phosphorus, pound-for-pound, out of any of the other fertilizers listed here.
Hair is a very slow release fertilizer, and is effective for 4 to 12 months. However, it is relatively easy to find, since it is a waste product of every barbershop.
The only problem is that hair from barbershops will often contain chemicals, such as hair spray or gel, which you may not want to mix into your garden soil.
Instead of applying hair directly into your soil, your best bet is to put it into a compost pile, along with some of the other phosphorus sources here. That way, it can break down over the course of several months to a year.
Hair also contains 12% nitrogen by weight, although it does not contain any potassium.
Enriched Rock Phosphate
Rock phosphate, also known as phosphorite, is a sedimentary rock with a high phosphorus content by weight. At 17 to 30% phosphorus by weight, enriched rock phosphate is one of the best sources of phosphate for growing crops.
Rock phosphate is often found in limestone and other sedimentary rocks. Rock phosphate has a very slow release time, and is effective for 5 or more years.
There are better sources of phosphate if you want a quick release of phosphorus into your soil. However, rock phosphate is a great source of phosphate if you want to apply it once and not need to do it again for year.
For more information, check out this article on rock phosphate from Wikipedia.
Keep in mind that rock phosphate contains no nitrogen or potassium.
Bone meal is made from crushed or ground bones and waste products from slaughterhouses. At 15% to 27% phosphorus by weight, it is just behind enriched rock phosphate in terms of phosphorus content.
Bone meal has a medium release time, and is effective for only about 6 weeks. One caution about bone meal is that it may burn plants if used in high amounts.
Instead of applying bone meal directly to plants, add it to your compost pile, along with some of the other fertilizers in this list. After a few months to a year, you will have a balanced compost mix with plenty of nutrients for your plants.
Remember that plants can only get phosphorus from bone meal if the soil pH is below 7.0 (acidic). The only way to tell for sure is to do a soil test (more on this later).
In addition to phosphorus, bone meal contains plenty of calcium, along with 2% to 6% nitrogen by weight. However, it contains no potassium.
For more information, check out this article on bone meal from Wikipedia.
Burned Cucumber Skins
This is one of the most surprising high-phosphorus fertilizers on this list. Burned cucumber skins contain 11% phosphorus by weight, making them a fairly good source of phosphorus on a pound-for-pound basis.
Burned cucumber skins also have a fast release time, meaning that they are effective for only a few weeks.
In addition to phosphorus, burned cucumber skins contain 27% potassium, making them a champion for providing this nutrient as well. Burned cucumber skins contain no nitrogen, however.
You can ask a local restaurant if they have cucumber skins available, since they will peel and slice many of them in the course of a day for salads.
Guano is the excrement of seabirds and bats. Bat guano is a fairly good source of phosphorus, containing 4% to 11% phosphorus by weight.
It is difficult to find bat guano on your own, so you will probably need to buy it from a store or online.
Bat guano has a medium release time, and is effective for perhaps a month or two.
One caution is that bat guano has a low pH (very acidic), so it should be used with caution to avoid burning your plants with a sudden change in pH.
Only use bat guano directly in soils with high pH, or else mix it into your compost pile to dilute the acidity.
Here is a fun fact for you: bat guano that accumulates over many years can eventually provide a source of rock phosphate once the excrement hardens into layers of rock!
Bat guano also contains 12.3% nitrogen and 2.5% potassium by weight, making it a great all-around fertilizer that provides plenty of each nutrient.
For more information, check out this article on guano from Wikipedia.
Fish meal is a powder made from ground up fish parts, including bones. Fish meal is a good source of phosphorus, containing 4% to 6% phosphorus by weight.
Fish meal has a medium release time, and is effective for 4 to 6 months.
Dry fish meal also contains 10% nitrogen by weight, although it does not contain any potassium.
For more information, check out this article on fish meal from Wikipedia.
Cottonseed meal is what remains after cottonseed oil is extracted from cotton seeds. Cottonseed meal has a 2.5% to 3% phosphorus, making it better than most manures in terms of phosphorus content by weight.
Cottonseed meal has a slow to medium release time, and is effective for 4 to 6 weeks. Remember that cottonseed oil is somewhat acidic, so it may be a good idea to mix it into compost instead of using it directly on plants.
Cottonseed oil also contains 4% to 6% nitrogen by weight and 1.6% potassium by weight, making it a good all-around source of the big three nutrients.
For more information, check out this article on cottonseed meal from Wikipedia.
Worm castings are the product of vermicomposting, where worms are used to help decompose vegetables and food waste. Worm castings contain plenty of organic material, in addition to their nutrient content.
Worm castings contain 2.5% phosphorus by weight. In addition, worm castings contain 1.5% nitrogen and 1.3% potassium by weight.
For more information, check out this article on vermicompost from Wikipedia.
Blood meal is a powder made from the dried blood of animals (often cattle or hogs), and like bone meal, is often a by-product of slaughterhouses.
Blood meal contains 1.5% phosphorus, making it better than most manures and composts in terms of percentage phosphorus by weight.
Blood meal has a medium release time, and is effective for 6 to 8 weeks.
Blood meal also contains 12.5% nitrogen and 0.6% potassium by weight.
For more information, check out this article on blood meal from Wikipedia.
There are many different types of manure, including cow, horse, pig, and chicken.
Cow and horse manure often contains only 0.2% to 0.7% phosphorus by weight.
Pig manure contains 0.5% to 1% phosphorus by weight.
Chicken manure contains 1% to 4% phosphorus by weight.
All of these manures have a medium release speed, and can be effective for two years.
Manures also contain small amounts of nitrogen and potassium as well, making them good all-around fertilizers. Just make sure to decompose manure completely before using it on your garden, to avoid burning your plants!
For more information, check out my article on manure.
Compost is made from kitchen scraps and yard waste, such as banana peels, orange rinds, grass clippings, and raked leaves.
Compost contains 0.5% to 1% phosphorus. It is a slow release fertilizer, and also contains nitrogen and potassium.
The best part about compost is that you can make your own in your backyard. For more information, check out my article on how to make compost.
Fertilizer For Flowering Plants
These specialized fertilizers contain more phosphorus than nitrogen or potassium. They are often labelled as blossom boosters or bloom boosters.
For example, Triple Super Phosphate from Easy Peasy Plants contains 44% phosphorus by weight. It is supposed to help with root growth, in addition to aiding fruit and flower formation.
If you want a more balanced high-phosphorus fertilizer, you can use something like Gaviota 10-30-10 fertilizer.
Can You Have Too Much Phosphorus In Soil?
Yes, it is possible to have too much phosphorus in your soil. Excessive phosphorus in soil can cause stunted plant growth by preventing plants from absorbing nitrogen.
However, there are other problems with excessive phosphorus in soil.
First of all, the excess phosphorus can move into ponds, lakes, streams, or rivers via runoff water, threatening water quality by causing algae blooms.
Excess phosphorus can also inhibit growth of beneficial bacteria in soil.
For more information, check out this article from UMass Amherst on too much phosphorus in soil.
The moral of the story is this: always get a soil test before adding any supplements to your soil. Make sure you really do have a phosphorus deficiency!
A soil test will also tell you if your soil is too acidic (low pH) or too basic (high pH), which can help you to decide which supplement to use.
For more information, check out my article on how to do a soil test.
Now you have a much better idea of which fertilizers (both natural and man-made) have high phosphorus content by weight. You also know how to choose which one to use based on the time it takes for the fertilizers to release nutrients.
Just remember that high phosphorus levels in water can cause algae growth on the water, or on the surface of soil, or in a greenhouse.
Also, keep in mind that cold soil can cause phosphorus deficiency in plants – even if there is plenty of phosphorus in the soil. For example, the leaves of tomato plants will turn purple due to phosphorus deficiency caused by cold soil.
If you want some ideas for how to add nutrients to your garden soil naturally, check out my article here.
I hope you found this article helpful – if so, please share it with someone else who can use the information.