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  • Writer's pictureJere Folgert

Understanding Phosphorus: Why Placement and Timing Matters for Plants!

Updated: Feb 27

Slow and Steady Wins the Race: Using Phosphorus Wisely in Your Garden

One important nutrient plants need is phosphorus, but it has a special quirk: it likes to stick to soil particles and doesn't move around easily. This means plants have a hard time "reaching out" for it, like grabbing a snack from a faraway table.

Think of it like this: imagine your phone charger is stuck in one spot on the wall, far from your bed. You wouldn't be able to charge your phone easily, right? That's kind of how it is for plants and phosphorus.

Phosphorus is a crucial element for plant growth, contributing to strong roots, vibrant blooms, and delicious fruits and vegetables. However, using it effectively requires understanding its unique characteristics and how to optimize its benefits for your garden.

The 4 R's of Phosphorus Application:

  1. Right Source: Choose a slow-release phosphorus fertilizer suitable for your soil and plants. Popular options include:

  1. Right Place: Apply the fertilizer around the base of your plants, where the roots can easily access it. Avoid applying directly to the stem, as this can damage the plant.

  2. Right Rate: Soil testing is crucial before applying any fertilizer, including phosphorus. It provides an accurate assessment of your soil's existing phosphorus levels and helps you determine the appropriate application rate to avoid over-fertilization. (

  • Follow the specific recommendations provided in your soil test report.

  • If you haven't conducted a soil test yet, consult university extension resources or reputable garden centers for general guidelines based on your plant types and soil conditions.

  1. Right Timing:  Generally, apply slow-release phosphorus fertilizer in early spring or fall.

  • Spring application: Provides nutrients as plants emerge from dormancy and begin their growth cycle.

  • Fall application: Allows time for the fertilizer to break down and become available to plants in the following growing season, while minimizing potential leaching over winter. (

The Role of Bacteria:

While some soil bacteria can help break down slow-release phosphorus sources and make them more readily available, relying solely on these bacteria for your phosphorus needs might be insufficient, especially if your soil test indicates a deficiency. Consulting a soil test and choosing an appropriate fertilizer source ensures your plants receive the necessary nutrients. (

Symptoms to Watch For:

Additional Resources:

Remember: By following these principles and utilizing reliable information, you can optimize phosphorus use in your garden, promoting healthy plant growth and protecting the environment from excess nutrient runoff.

Here's what you need to know:

  • Phosphorus doesn't travel far: It might only move about an inch in a whole season, which is way too slow for plants to reach it if the fertilizer isn't placed close enough.

  • Levels can vary: Because phosphorus sticks where it's put, the amount available to plants can be different in different parts of a field, even in the same row!

  • Timing and placement are key: The best way to help plants access phosphorus is to put it near their roots when planting, like placing your charger close to your bed. This is called in-furrow fertilization.

  • Fall application can help: If in-furrow isn't possible, applying fertilizer in the fall gives it more time to dissolve and move into the root zone before spring planting.

  • More on the surface, double the amount: If applying on the surface, you need to use twice the amount you would for in-furrow, because some of it won't be as readily available to the plants.

Remember, understanding phosphorus immobility helps us place it properly so plants can easily access this important nutrient and grow strong!

Here's the scoop on slow-release phosphorus sources:

  • They release phosphorus gradually: These sources, like manure and compost, break down slowly, releasing phosphorus bit by bit throughout the growing season, like a steady stream of trail mix.

  • Manure is a champion: It's a fantastic source of slow-release phosphorus for your plants.

  • Bacteria are tiny helpers: Scientists are studying special bacteria that live in soil and help break down these slow-release sources, making the phosphorus more accessible to plants.

  • Slow and steady doesn't always win: While slow-release is good, it can be tricky to make sure plants have enough phosphorus exactly when they need it. Researchers are looking for ways to improve the process.

Remember, different sources of phosphorus have their own advantages and disadvantages. Understanding them helps us choose the best option for our plants!

RECAP. Experts are here to help! We want farmers to feel confident about their fertilizer decisions, so we recommend following the "4 Rights" approach:

1. Right source: Not all fertilizer is created equal! Some release phosphorus quickly, while others do it slower. MUniversity Extensions can help farmers pick the best type for their specific needs.

2. Right Location: Putting fertilizer in the right spot near the roots is key. This helps plants absorb the nutrients they need and avoids wasting fertilizer.

3. Right Time to Apply: Timing is everything! Applying fertilizer at the right time ensures plants have the nutrients they need exactly when they need them.

4. Right quantity: Using the correct amount of fertilizer is crucial. Too much can be harmful to the environment and can even cost farmers money.

Phosphorus is super important for plants, but it can also cause problems like algae blooms if too much ends up in waterways. By following the "4 Rights," farmers can:

  • Help their crops grow strong and healthy.

  • Protect water quality for everyone.

  • Save money by using fertilizer efficiently.

Contact your local University or County Extension. They are a great resource for farmers, including Garlic Farmers. They can help you understand the best practices for fertilizer use and ensure you have a successful and sustainable growing season.

Testing soil and determining fertilizer rates depends on the type of crop and the results of soil tests. The Olsen P test is commonly used for most soils, except for very acidic ones. However, it may not be accurate for those soils as it might show more phosphorus available than there actually is.

Knowing what's in your soil is key to growing healthy crops and using fertilizer efficiently. Here's the lowdown:


  • Different crops need different nutrients, so testing your soil helps you know what's available.

  • The Olsen P test is common for most soils, but it can be unreliable in very acidic soils.

Reading the results:

  • Let's say your test shows 12 parts per million (ppm) of phosphorus.

  • Based on this level, applying 30 pounds of phosphorus (P2O5) per acre for wheat or canola might be recommended, and 20 pounds for peas or lentils.

  • The critical level is the point where no additional fertilizer is needed because the soil has enough. In this case, it's 16 ppm.

Important points:

  • Even at an average of 16 ppm, parts of your field might still lack phosphorus. Sample from various areas for accurate results.

  • Farmers can also consider how much phosphorus crops remove when estimating fertilizer needs (maintenance approach).


  • This is a simplified explanation, and specific recommendations might vary depending on your location and crops.

  • Always consult with local agricultural experts for the best advice tailored to your situation.


Groeat Farm

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