If your soil already has lots of phosphorus, you might not want to use a high-phosphorus fertilizer. Luckily, there are some options that have low or zero phosphorus levels.
So, what fertilizer is low in phosphorus? A package of low phosphorus fertilizer has zero (or close to zero) as the second number. For example, 10-0-10 fertilizer contains no phosphorus at all. A 3-1-2 fertilizer contains only 1% phosphorus by weight. Some soil amendments (such as feather meal) are natural low phosphorus fertilizers.
Of course, there are lots of low-phosphorus fertilizers that add other nutrients, including nitrogen, potassium, calcium, and sulfur.
In this article, we’ll start off by looking at some common low-phosphorus fertilizers. Then we’ll get into the reasons to use low phosphorus fertilizers.
Let’s get going.
What Fertilizer Is Low In Phosphorus?
Fertilizers that are low in phosphorus have a low (or zero) second number on the package. For example:
- A package of 10-0-10 contains no phosphorus at all (it contains 0% nitrogen by weight).
- A package of 3-1-2 is low in phosphorus (it contains 1% nitrogen by weight).
Every fertilizer package has a set of three numbers on the label. These three numbers indicate the nutrient content, by weight, for the “big three’ nutrients.
The “big three nutrients” have initials N-P-K, which stand for:
- N = nitrogen (the “greening” nutrient, since it is used to make chlorophyll via photosynthesis)
- P = phosphorus (supports energy transfer for root and flower growth)
- K = potassium (necessary for photosynthesis and supports development of seeds and fruit)
For example, a fertilizer labelled as 5-10-30 contains:
- 5% nitrogen by weight
- 10% phosphorus by weight
- 30% potassium by weight
- 55% filler (the other 45% is nutrients: 5% + 10% + 30% = 45%)
Thus, a 100 pound bag of 5-10-30 fertilizer would contain 5 pounds of nitrogen, 10 pounds of phosphorus, and 30 pounds of potassium, along with 55 pounds of filler.
To learn more, read my article on fertilizer numbers and NPK ratios. Remember that the NPK nutrients are 3 very important ones for plant growth – but there are others (such as calcium, magnesium, sulfur, and iron).
If you want a fertilizer that is low in phosphorus, seek out a bag of fertilizer with a smaller second number on the label. You can even find some fertilizers that contain no phosphorus at all (for those, the first number will be a zero).
Remember: a complete fertilizer contains all three of the “big three” nutrients: nitrogen, phosphorus, and potassium (in varying amounts – see the package label for details). If you want a fertilizer with no phosphorus at all, don’t use a complete fertilizer.
Instead, look for a low-phosphorus or phosphorus-free fertilizer, such as those listed below.
What Fertilizer Has No Phosphorus? (Phosphorus-Free Fertilizers)
Here are some fertilizers that contain no phosphorus at all (the second number on the package label is zero).
Feather meal is made from poultry feathers and is a byproduct of processing the animals. The feathers are heated under pressure and ground down into a powder to form the meal.
Feather meal is not water soluble, and releases its nitrogen slowly. It is effective for 4 to 6 months.
Feather meal contains 15% nitrogen by weight, making it another excellent source of nitrogen for your soil. It should be added to a compost pile to aid in decomposition, so that the nitrogen becomes available for plants.
Feather meal does not contain any phosphorus or potassium.
For more information, check out this article on feather meal from Wikipedia.
Sulfate of Potash Magnesia
Also known as potassium magnesium sulfate, this fertilizer contains 22% potassium by weight, making it a great potassium supplement.
Sulfate of Potash Magnesia is a specific type of potash, which means that it contains potassium in water-soluble form. It contains 11% magnesium by weight, but it does not contain any nitrogen or phosphorus.
For more information, check out this article on potash from Wikipedia.
Natural Alternatives 5-0-5 Plant Food
This fertilizer contains 5% nitrogen and 5% potassium by weight, but no phosphorus. It is enhanced with beneficial microbes to promote soil health.
This 6.5 pound container from Natural Alternatives covers up to 200 square feet, which should help with a decent sized garden (you only need to fertilize near the plants, not in the spaces between plants and rows).
What Fertilizer Has Low Phosphorus?
These fertilizers have some phosphorus, but in low amounts.
Greensand is a type of sandstone, often rich in marine fossils, with a green color. It is also porous, meaning that it can retain both water and minerals.
As a fertilizer, greensand contains 5% to 6% potassium by weight. It also contains 1% to 1.5% phosphorus by weight, although it does not contain any nitrogen.
Greensand has a very slow release time, and is effective for 5 years or longer.
For more information, check out this article on greensand from Wikipedia.
Kelp is a large seaweed that grows in “forests” underwater. Kelp has a brown color and grows in nutrient-rich water.
As a fertilizer, kelp contains 4% to 13% potassium by weight, making it a fairly good source of this nutrient. Kelp also contains 1% nitrogen and 0.5% phosphorus by weight.
Kelp has a slow release speed, and is effective for 4 to 6 months.
For more information, check out this article on kelp from Wikipedia.
What Fertilizer Is High In Nitrogen & Low In Phosphorus?
The following fertilizers are high in nitrogen and low in phosphorus.
Propeat 10-0-10 Lawn Fertilizer
This fertilizer contains 10% nitrogen and 10% potassium by weight, but no phosphorus. The nutrients are released by peat moss, which also adds organic material to your soil.
This 25 pound bag of Propeat from Home Depot is enough for 5,445 square feet of lawn. You could also use it in your garden for growing herbs, fruit, or vegetables,
Lesco 15-0-15 Turf Fertilizer
This fertilizer contains 15% nitrogen and 15% potassium by weight, but no phosphorus. It also contains 3% iron by weight.
This 50 pound bag of Lesco from Home Depot is enough to cover 7,500 square feet of lawn. It is formulated for warm-season grasses, but you can also use it in the garden.
Gordon’s 20-0-0 Liquid Lawn & Pasture Fertilizer
This fertilizer contains 20% nitrogen by weight, but no phosphorus or potassium. This is a fast-release fertilizer, which is useful if your plants need nitrogen right away.
Fertilizer Use Warning
There are some things to think about before using fertilizer, whether it is low-phosphorus or not.
Do A Soil Test
First, get a soil test before you add any fertilizer to your garden. Knowing the soil pH and nutrient levels will help you to make good decisions about what to use to improve your soil.
You can buy a do-it-yourself soil test kit at a garden center or online. You can also get a soil test from a lab at your local agricultural extension office.
You will need to take a soil sample from your yard (the extension office will have instructions on their website). Once you send in the sample, they will be able to give you a more detailed analysis and even recommendations, depending on what you are growing.
You can also take a soil sample from your yard and send it to the lab at your local agricultural extension office.
For more information, check out my article on how to do a soil test.
Follow Fertilizer Label Instructions
When using fertilizer follow any instructions on the package before you add it to your garden. Adding too much fertilizer too fast will result in fertilizer burn, which can damage or kill your plants.
Remember: you can always use more fertilizer later, but it is difficult to remove it after adding too much. This is especially true for fast-release fertilizers, which are water-soluble and can easily burn your plants.
For more information, check out my article on over fertilizing plants.
Pay Attention To Overall Soil Health
Finally, remember that the best strategy for a green garden is to look after soil health first. Use fertilizer as a supplement to compost, manure, mulch, and other more natural methods.
There are several important factors for soil health, including:
- Soil Texture (clay, loam, sand)
- Soil Organisms (beneficial bacteria, earthworms)
- Water Retention (drainage)
These things cannot be fixed by any fertilizer.
Luckily, adding compost or aged manure can help with all of these factors:
- Compost will help clay soil to drain better, and it can make sandy soil retain a little more water.
- Organic material in compost or manure attracts beneficial soil organisms, which improve soil quality by making nutrients available to plants.
Natural Low-Phosphorus Fertilizers
There are also some ways to provide low-phosphorus nutrition for your garden in a more natural way.
Low Phosphorus Compost
The phosphorus content of compost depends on what you put into the pile. For example, these are some high-phosphorus materials to avoid in a low-phosphorus compost pile:
- Bone Meal
- Fish Meal
It is a good idea to add compost to your garden first. This will provide nutrients and organic material to your garden.
This material slowly decomposes over time, due to bacteria and earthworms in the soil. The nutrients in this material then become available to plants gradually.
The best thing about compost is that you can make it yourself at home, from yard waste and kitchen scraps
For more information, read my article on making your own compost.
A low-nitrogen manure will add organic material to soil, along with other nutrients – all without burning your plants. However, not all manure is created equal.
Chicken manure has a lot more phosphorus, at 1% to 4% phosphorus by weight (depending on the water content).
You can also use low-phosphorus mulch over the soil in your garden. Mulch has several benefits, including:
- Insulating soil against temperature fluctuations
- Retaining water by preventing evaporation
- Providing organic material for your garden (after it decomposes).
Some common low-phosphorus mulches that you can use are wood chips or wood ash from a fire. According to the University of Maine, the average wood ash has a nutrient content of 0-1-3, or 0% nitrogen by weight, 1% phosphorus by weight, and 3% potassium by weight.
For more information, check out my article on using wood ash in your garden.
There are some soil additives that have no phosphorus at all, but they still add important plant nutrients including:
- Epsom salt (magnesium sulfate) – this salt adds magnesium and sulfur to your soil. You can learn more about Epsom salt here.
- Chelated iron – this substance has iron in a form that plants can absorb. You can learn about other iron supplements for soil here.
- Lime (calcium carbonate) – this substance adds calcium to soil. It is also used to raise soil pH.
- Sulfur – adds sulfur to soil. It is also used to lower soil pH. For more information, check out my article on raising soil pH and my article on lowering soil pH.
Some additives (like Epsom salt and chelated iron) can be dissolved in water for foliar feeding (where you spray the fertilizer solution on the leaves of plants).
This method works because plants can absorb the water and nutrient mix through their leaves.
Other common soil additives, such as hair, enriched rock phosphate, and bone meal do contain higher levels of phosphorus. You should avoid using these additives if a soil test shows that you have too much phosphorus in your soil.
You may find that your soil is still short on nutrients after adding compost or aged manure. In that case, low-phosphorus fertilizers can work as a good supplement to add what is missing.
Why Use A Low Phosphorus Fertilizer?
There are several reasons to use a low-phosphorus fertilizer, one or more of which may apply to your garden.
Excessive Phosphorus In Soil
First of all, you may have excessive phosphorus in your soil. This could be due to overuse high-phosphorus fertilizers in the past.
Too much phosphorus can also harm water systems by encouraging algae blooms. These blooms lower oxygen levels in the water, killing fish and other aquatic life.
Nutrient Deficiency In Soil
Your soil may also have a deficiency of other nutrients, such as:
There might already be plenty of phosphorus in your soil. If so, a low-phosphorus fertilizer would be a good idea.
Now you have a much better idea of which fertilizers are low in phosphorus and where to find them. You also know how to provide organic material to your garden without adding too much phosphorus.
You might also be interested in reading my article on low nitrogen fertilizers.
I hope you found this article helpful. If so, please share it with someone who can use the information.