How to Add Phosphorus to Soil: 8 Different Ways

If your garden is performing poorly, your soil could either lack phosphorus or plants are blocked from using it. Over-fertilization, run-off, leaching, too much acidity, soil compaction, herbicide injury, and insect pressure can all lead to poor phosphorus uptake. For these situations, you'll need to know how to add phosphorus to your soil.

The quickest way to add available phosphorus is to apply fertilizer with a higher percentage of phosphorus in the NPK ratio, such as a 10-20-5. But if plant uptake is the underlying cause, adding conditioners to release phosphorus bound up in the soil is more efficient with less potential for build-up that can cause additional problems. In some cases, the best remedy may be a combination of both. A soil test can pinpoint the cause and help you choose the best approach to correct the problem.

What Does Phosphorus Do For Soil?

Phosphorus is one of three elements essential to all plant growth. Along with nitrogen and potassium, phosphorus is the P in the NPK formula found on garden fertilizer labels. It provides secondary minerals and supports nutrient uptake needed for early root growth, plant cell and seed development, winter hardiness and the efficient use of water. It supports photosynthesis and helps manufacture chlorophyll which gives foliage its green color.

Phosphorus is a naturally occurring element in all soil but not always in a form that allows plants to use it. Signs of phosphorus deficiency include stunted growth, weak stems, dieback, yellowing or red-purple discoloration on leaves, small or deformed fruits and flowers and failed harvests.

Here are eight ways to increase available phosphorus and improve plant performance in your garden.

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High Phosphorus Fertilizers

Commercial fertilizers with a greater percentage of phosphorus release it for immediate plant uptake and may be labeled bloom boosters or bloom enhancers. They can be liquids, granules, or foliar sprays that act quickly to produce blooms on vegetables, fruits and ornamentals. Commercial fertilizers are quickly depleted and repeated applications can harm plants with salt buildup and affect pH balance. Applied in autumn, usable phosphorus can remain in the soil for up to six months.
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Animal Manure

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All manures add phosphorus to soil but in relatively small amounts. Chicken and horse manures contain the highest amounts with about 80 percent taken up by the soil immediately. Fresh manure contains pathogens and can lose some nutrient value through aging. Still, manure composted using high heat and well-aged manure are the safest choices for edible crops. It can also be spread fresh in autumn and tilled under in spring.
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Bone Meal

An organic fertilizer that feeds plants from one to four months, bone meal is fine or coarse powder ground from animal bones and animal processing waste. It contains a high amount of phosphorus at 12 to 24 percent immediately available to plants. It's usually applied once a year at planting time, but can also boost phosphorus for individual plants or crops by side dressing and watering in. It breaks down best in soil with a balanced to slightly acidic soil.
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Fish Emulsion

Fish emulsion provides a phosphorus boost to plants with rapid results when used as a foliar spray. It's an organic fertilizer made from whole fish and fishing industry by-products. It works fast but is also used up quickly and can be applied on a consistent schedule throughout the growing season. Unlike commercial formulas, fish emulsion doesn't cause harmful salts to accumulate in soil.

Continue to 5 of 8 below.
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Worm Castings

Compost with worm castings is an organic soil amendment that may add some phosphorus to soil, but more importantly, it frees up existing phosphorus. If your soil test results show adequate phosphorus levels, but your garden is struggling, worm castings help eliminate the poor uptake problem. This is a specialty organic soil conditioner with plenty of micro-nutrients but it requires special materials and equipment and commercially sold product can be pricey.
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Compost

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Compost is a soil conditioner made up of organic materials partially broken down before adding to soil. It can be applied before, after or at the time of planting and worked in by tilling or digging. Compost replaces depleted nitrogen, phosphorus and potassium as well as secondary minerals and nutrients, however, very little phosphorus is immediately available to plants. This makes compost an ongoing practice for improving soil performance with the greatest benefit from repeated annual applications.
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Lime

Phosphorus breaks down best in soil with a balanced pH level of 7 to 7.5. Acidic soil can bind it and prevent plants from using it. When soil test results show high acidity, garden lime can balance pH and release phosphorus that was previously unavailable. It consists of granulated limestone or dolomite with high concentrations of calcium and magnesium. Lime is applied once just before planting.
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Rock Phosphate

Rock phosphate is mined rock with high levels of phosphorus. Basalt, granite and rhyolite are examples of this type of rock. Soft rock phosphate is a powdered form added to soil at planting time. Rock phosphate is also used in larger form as a decorative mulch. This is a slow release form that takes five years to break down completely.

FAQ

What is the fastest way to increase phosphorus in soil?

Commercial fertilizer with a greater percentage of NPK phosphorus, composted manure, and foliar fish emulsion all rapidly boost available phosphorus.
What is a good source of phosphorus for plants?

Chicken and horse manure, bone meal, fish emulsion and rock phosphate are all good sources of phosphorus for plants. Fertilizers with a higher second number, such as 10-20-5, act quickly to boost phosphorus for plants.
Does Epsom salt contain phosphorus?

Epsom salt does not contain any of the primary elements needed by plants; nitrogen, phosphorus or potassium. It is made up of magnesium, sulfur and oxygen.

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