What is Nutrient Deficiency and Nutrient Toxicity?

Summary of Nutrient Deficiencies and Toxicities in your high-value crops

The nutrient feeding schedule of your high-value plants is a bit tricky and it’s quite natural for a novice grower to add too much fertilizer to the plants expecting to get better growth. However, this is not the correct way to provide nutrients to plants. Excess salts present in the nutrient solution or growing medium block nutrient uptake that directly affects the growth of plants. This condition is described as nutrient toxicity and/or nutrient deficiency.

There are a number of things related to nutrient toxicity that growers must understand before adding fertilizers or nutrients to their plants. We explain them below:

Understanding Nutrient Lockout: It’s the most common consequence of presence of excess nutrients in the solution. So what exactly happens? When one nutrient is present in large excess, it conflicts with absorption process of other essential nutrients. Thus, plants cannot access that essential nutrient or a group of essential nutrients because the excess nutrient or the toxic substance blocks the roots. Subsequently, plants suffer from nutrient deficiencies due to toxicity. Nutrient lockout can also occur from a chemical reaction in the nutrient solution, which may produce toxic substances capable of altering the chemical properties of nutrients.

Too High or Too Low pH: Nutrients get locked up in the form of undissolved salts and other compounds if the pH is kept too high or too low from the standard. A new grower might reckon that his/her plants are not growing due to lack of proper nutrients, and he supplements the plants with more fertilizers…What happens next? He simply aggravates the condition- the nutrient load increases and plants show abnormal signs of growth. Thus, you can see that nutrient toxicity and nutrient lockout can also occur from pH alterations.

How Toxicity Damages Your Plants


  • Excessive soft and dark green foliage
  • Slow root growth
  • Leaves turn brown gradually and fall off
  • Deformities in fruit and flowers


Many strains can tolerate high levels of phosphorous. Toxicity can still occur under pH fluctuations. Presence of excess phosphorous interferes with uptake and stability of calcium, iron, magnesium and zinc.


Toxicity of potassium is quite uncommon. It’s assumed that if your plants absorb magnesium and manganese very slowly, then phosphorous could prove to be toxic.


It’s a rare condition in plants and is difficult to figure out. However, under extreme toxic conditions, magnesium hinders absorption of calcium.


  • Causes deficiency of Zinc and Iron
  • Mottling of leaves
  • Chlorosis in young leaves
  • Later leaves turn dark rusty brown or dark orange


Presence of significant amounts of zinc in the nutrient solution is extremely toxic for plants. It conflicts with uptake of iron. The signs are:

  • Plants become chlorotic
  • Plants die rapidly


Iron usually doesn’t cause toxicity problems to plants. However, if the composition is extremely high in nutrient solution, it will severely hamper uptake of phosphorous. Bronze patches on leaves or small dark brown spots often indicate zinc toxicity. An important thing to remember is over application of Fe chelators is fatal.


  • Reduction in leaf size
  • Stunted growth
  • Scorching of leaf edges
  • Yellowing of leaves


Excess calcium precipitates with sulfur in the solution itself leaving behind residue in the tank. The solution also becomes cloudy. Furthermore, it makes plant starve for potassium and magnesium.


  • Induces iron deficiency
  • Suppressed root growth
  • Reduced branching
  • Chlorosis
  • Roots become abnormally dark and thick
  • Stunting of plants
  • Reduced branching


Though toxic symptoms are rare, it usually happens due to continuous accumulation. Excess molybdenum causes discoloration of leaves.

After reading this article, you must have understood that adding more nutrients is not the correct way to get bigger and richer yields. When toxicity conditions prevail, flush your plants with water or replace the nutrient solution after checking its pH. Make sure that you read the feeding schedule properly before growing your plants.

4 thoughts on “What is Nutrient Deficiency and Nutrient Toxicity?

  1. Mahmoud Wasfy says:

    When do we call it Deficiency or Toxicity, i.e. what percentage plus or minus the required nutrient level is acceptable?

  2. robert kayne says:

    To: Wasfy

    The leafs and stems will show us the deficiencies and toxicities. Each grow stage, acceptable, has a specific required PPM level.

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