Plant health

How to identify phosphorus nutrient deficiency in plants

By Michelle Joe on June, 18 2021
Back to main Blog
Michelle Joe

Michelle is a storyteller who is passionate about growing.

Are your plants showing signs of poor health? You have identified it isn’t pests that are contributing towards the issues for your crops, but a nutrient imbalance or nutrient deficiency. Plants require the right amount of nutrients in order to thrive and if there is too much or a lack of a particular type of nutrient, this will be visibly evident in your plants.

Common deficiencies involve a change in colour, shape or growth of your plants. In this blog post, we take a deep dive into one of the macronutrients, phosphorus, and how this nutrient type plays an important role in your plant’s overall growth development. We’ll demonstrate how to identify a deficiency in phosphorus, what the cause is and ideally, how to prevent this before your plants get affected.

What is phosphorus?

Phosphorus (P), is a macronutrient and one of the “big three” primary nutrients in commercial fertilisers - Nitrogen (N), Phosphorous (P) and Potassium (K).

Nitrogen, Phosphorus and Potassium are essential nutrients for plant growth


Growth factors related to phosphorus are:

  • The increase of stalk strength
  • Better seed yield and formation of flowers
  • Accelerated root development
  • The maturity of a crop in its early days
  • Better resistance to diseases
  • Improved crop quality and development throughout the whole plant life cycle


It can be difficult to diagnose one nutrient deficiency as there could be a combination that is causing the symptoms in your plants. Plants require a range of both macronutrients and micronutrients to flourish. You will require larger amounts of macronutrients which consist of phosphorus, nitrogen, potassium, calcium, magnesium and sulfur. Micronutrients are needed in smaller doses; these include zinc, iron, copper, boron, manganese and molybdenum.

The key is not only giving the plants these nutrients but ensuring the right amounts are given. 

Why is phosphorus important?

Similar to how food is crucial for humans in order to gain energy to maintain the body’s structure and system – the same applies for plants.

Phosphorus is a vital nutrient found in fertilisers and is noted especially for its job in capturing and converting the sun’s energy in a way that makes it useful for the growth, vitality and health of plants. Phosphorus is an essential element to building proteins that assist with plant structure, the production of seeds and genetic transfer.

Phosphorus is essential to a plant’s growth, but if you have too much phosphorus or too little, this will cause problems with the health of your plants. 


How to identify a phosphorus deficiency in plants


Phosphorus deficiency in plants

A phosphorus nutrient deficiency has some tell-tale signs:

  • The older leaves of your plants will be the first to be affected
  • Leaves will be a darker green colour
  • Brown leaves or leaves tinged with purple, bronze or red
  • Stunted leaves where the growth and leaf surface will be underdeveloped
  • A delay in the development of young roots which causes difficulty for water and nutrient intake
  • When left untreated, leaves can develop brown spots and necrosis


What is the cause of phosphorous deficiency?

Phosphorus is a key component of plant DNA and RNA which helps to convert the genetic information of DNA into proteins. It is pivotal in plant development, photosynthesis and cell division. Phosphorus also contributes to the stamina of your plant, helping it endure other health issues and diseases.

A common cause for phosphorus deficiency is an imbalance of nutrients, an incorrect pH level, the concentration of iron in your growing medium is too high, or it may be affected by extreme cold conditions which is something to be mindful of during the colder months and growing outside.


How do you treat a phosphorus deficiency?

Prevention is always a better solution, therefore understanding what causes deficiency in plants will alleviate the treating process. Ensure fertilisation is at its optimum and there’s ease of nutrition consumption by taking into account the pH levels using a pH meter or pH pen.

However, if you’re seeing signs of phosphorus deficiency, here are some steps on how to tackle it and ensure your plants are healthier going forward.  

  • Absorption of phosphorus depends on the temperature. Check the temperature of the root zone and if it falls below 15 degrees Celsius, a deficiency in phosphorus is likely to occur. To learn more about the importance of temperature for your plants and how to lower or increase root zone temperature, read more here.
  • Apply bone meal to treat your plants as this supplement is rich in phosphorus and will assist with ensuring your new plants are healthy.
  • Ensure your pH is correct and is measuring appropriately for your specific plants. Manage this by adding nutrient mixes or fertilisers to it. Read more information around pH and check out our measuring pH chart here to see how your plants are measuring up.
  • Ensure root zone moisture is not too wet by extending the intervals you water your plants or supply less water at one given time.


It can be tricky to diagnose which nutrients your plants are lacking and it could be a mix of various nutrient deficiencies or toxicities at one given time. We highly recommend getting in touch with your local plant nutrition expert or growing store to ensure you purchase the correct product for your specific nutrition deficiency. This also applies when selecting the correct solution for your chosen growing medium – whether for soil or hydroponics.

Prevention is the recommended route to ensure healthy thriving plants. By regularly monitoring the pH, and temperature using a pH pen meter, you are less likely to face nutrient deficiency problems. We have created four plant health checks you should be doing every day to ensure you are on the prevention route for your plants.

To find out more about the nutrient uptake fundamentals of pH, EC and temperature, check out this article on measuring and adjusting your fundamental parameters.


Further resources

To learn more about what we have covered, here are some more useful resources to help you along the way with your growing journey:



Submit a comment