Plant Nutrients and Deficiencies


Oxygen (from water and the atmosphere)

Hydrogen (from water)

Carbon (from the atmosphere)



Mineral nutrients are broken down into macro and micro nutrients.Within these, some are mobile nutrients (MN) problems tending to affect older leaves first and immobile nutrients (IN) with problems tending to affect younger leaves first:


Nitrogen (N) comes from the air, is a part of all living cells and is essential to energy transfer and chlorophyll. (MN)

Phosphorus (P) like nitrogen is an essential part of photosynthesis and growth. Involved in the production of oils, starches and sugars. (MN)

Potassium (K) other than nitrogen, this is absorbed in large amounts. Helps with fruit quality. (MN)



Calcium (Ca) essential for plant cell wall structure (IN) Note: The uptake of calcium can be affected by the General Hardness of your water.

Magnesium (Mg) helps activate plant enzymes for growth. (MN)

Sulphur (S) essential food for plants, improves roots and seed production. (IN)


Also known as trace elements

Iron (Fe) essential for forming chlorophyll (IN)

Copper (Cu) important for reproductive growth (IN) (but can be harmful to fish)

 Zinc (Zn) part of the enzyme systems which transform carbohydrates (IN)

Manganese (Mn) helps breakdown carbohydrates (IN)

Boron (B) helps regulate nutrients and is essential for seed production (IN)

Molybdenum (Mo) helps use nitrogen (MN)

Chloride (Cl) helps metabolism. (MN)




pH plays an important part in the plant’s ability to absorb the nutrients it needs for healthy growth. Maintaining the correct balance helps avoid nutrient lockout. The pH effects all three of the key elements; fish, bacteria and plants, as they all prefer slightly different environments.

Note: Sometimes deficiencies have similar symptoms, and can also be affected by the uptake of other nutrients. Be sure you are treating the correct deficiency before making radical changes to a system.



Iron is one of the only elements that will need to be managed regularly, especially if pH is high. If the pH is 8.0 or higher, plants find it difficult to absorb iron. This is called ‘nutrient lockout’.

Why do plants need iron? Iron is essential for the formation of chlorophyll.

Identifying Deficiencies : Characterised by chlorosis (yellowing of the leaves) but can easily be confused with magnesium deficiencies.

Treating Deficiencies : Chelated iron can be added to larger systems once a month. For young (higher pH) systems, FeEDDHA chelated iron is  better as it can be absorbed up to pH 9.0 – the down side to this is it will dye your water red.

For mature systems, with a pH up to 7.5, FeDTPA is useable – and will not dye your water.

Note: Some chelated iron is toxic, so ensure you buy the correct one.


In some cases, calcium deficiency can be attributed by plants not losing/drawing enough water – for example poor ventilation or high humidity within the growing area.

Why do plants need Calcium? Calcium is essential for regulating osmotic pressure and for cell wall structure.

Identifying Deficiencies : Younger growth is affected first, ‘burnt’ looking tips, blossom end rot – dead patches, especially on fruit.

Treating Deficiencies : Calcium chloride can be diluted as a foliar application, alternatively chelated calcium or lyme can be added to the water. Please Follow product instructions.


Potassium is often lacking in aquaponics, this largely affects fruiting or flowering plants. Also too much Calcium or Magnesium in the system can mean potassium becomes unavailable to the plants.

Why do plants need potassium? They need it for photosynthesis, gas exchange on the leaves, synthesising proteins and more.

Identifying Deficiencies : Older growth will usually be affected first by interveinal chlorosis (yellowing between veins), poor root growth in older plants, ‘burning’ of leaf edges.

Treating Deficiencies : Kelp meal, seaweed extracts into the water, or banana skin into a growbed are our safest recommendations.  If you are suffering a particularly bad Potassium problem; Potassium carbonate, hydroxide, sulphate or caustic lye can be diluted to water (amount for each aquaponic system will vary) alternatively as a foliar application, a drop or so of potassium chloride can be fully diluted and used directly on leaves.


Phosphorus is a key component for plants, and isn’t often lacking in aquaponics systems. Before treating Phosphorus deficiencies, please note that it can be useful to fruiting or flowering plants, but adding Phosphorus can over stimulate leafy plants, so in mixed systems it isn’t always recommended.

Why do plants need Phosphorus? It is important for the distribution of energy, protein cellular metabolism.

Identifying Deficiencies : Purpling/Bluing of leaves

Treating Deficiencies : Phosphorus is available in a rock form or as a powder – this can be added in tiny quantities directly to the grow-bed or sump. Note: Adding it can cause algae blooms.




When establishing your aquaponics system, it will take time for the system to mature. Adding organic seaweed extract can help the bacteria establish, as can adding worm castings. Once matured, this should no longer be necessary and you can test the strength of the nutrients in the water using an EC meter .

Adding household fertilisers is harmful in aquaponics, and should not be done. If you do see deficiencies in your plants, there are many ways to rectify them – it could simply be that your system is still young. When treating deficiencies, do not add them directly into the fish sections.

Note: Treating deficiencies in plants either in aquaponics or otherwise, is often best off being done in the morning or the evening, especially when applying foliar applications.

See our other pages for notes on pest control and physiological disorders.

Facebook Iconfacebook like buttonTwitter Icontwitter follow button