Problem Identifier / Nitrogen Toxicity in Plants

How to Fix Nitrogen Toxicity in Plants

Nitrogen Toxicity Cannabis
Nitrogen toxicity on cannabis leaves.

Nitrogen is a nutrient required for healthy plants. Many healthy plants have a nitrogen content of three to four percent. Plants need more nitrogen than many of the other nutrients because it is essential for photosynthesis. Nitrogen is also necessary for building proteins. If plants are denied protein, the result is death.

Nitrogen enables cells to use and conserve energy for metabolism. Nitrogen is essential for nucleic acids including DNA. This is what enables plants to reproduce and grow. Plants are unable to survive if there is not enough nitrogen available.

How does Nitrogen Toxicity Affect the Quality of Your Plant?

Nitrogen toxicity in plants results in clawed, shiny and abnormally dark green leaves, slow growth and weak stems. A claw is a leaf bent at the tips with a talon-like shape. Leaves often have a strange cupping or curving. Once the leaves become claws, they will turn yellow and die. If nitrogen toxicity is not treated, the leaves will eventually turn brown or yellow and fall off.

Toxicity in plants is usually the result of giving too much nitrogen, despite the large quantity required. Too much nitrogen affects plant quality because it negatively impacts photosynthesis. Excess nitrogen in cannabis plants will prevent the correct formation of buds, reduce both yields and potency and can cause inferior buds.

Symptoms of Nitrogen Toxicity in Plants

Nitrogen Toxicity Tomato
Nitrogen toxicity in tomato plants.

The most common symptoms of nitrogen toxicity in plants include:

  • Abnormally dark green foliage and leaves
  • Turned down leaf tips
  • Yellowing leaves
  • Nutrient burn
  • Clawed leaves
  • Plant stress
  • Spots on leaves often resulting in death

Nitrogen toxicity has a slightly different effect on numerous strains. Certain plants do not experience clawing, but the leaves turn an abnormal dark green. The tips of leaves on other plants will bend as much as 90 degrees. Some leaves begin to curl into claws, then turn brown or yellow prior to falling off. In most plants, the foliage and leaves become dark green, and the tips of the leaves turn downwards.

Nitrogen toxicity often causes nutrient deficiencies leading to yellowing on the impacted leaves. Nutrient burn frequently accompanies nitrogen toxicity. Sometimes, the clawed leaves are random with only certain leaves affected. If there are issues with pH levels or heat, the clawing worsens due to the extreme stress placed on the plants.

When a plant becomes stressed, more water is absorbed to help accommodate for diminished defenses. This increases the nitrogen levels, worsening the toxicity. If the nitrogen toxicity is not treated, the leaves will eventually turn yellow, spots will appear, and the plant will die.

Possible Confusion with Other Symptoms

  • Strange cupping or curving confused with overwatering the plant
  • Iron deficiency causes leaves to yellow
  • Confused with light burn since this is one of the symptoms
  • Similar yellow coloration as a nitrogen or sulfur deficiency
  • Often confused with fluctuating pH ranges
  • Similar clawed leaves like windburn

What Causes Nitrogen Toxicity?

Nitrogen toxicity is most frequently caused by:

  • Feeding plants excessive nutrients
  • Too much nitrogen in the soil

Toxicity is often caused by keeping the levels of nitrogen stable without making any adjustments to the nutrients provided. Although there are general rules for plant care, each plant needs a specific nutrient mixture to achieve optimal growth. Prior to using any treatment for nitrogen toxicity, all other potential causes should be eliminated. This is because a lot of nitrogen is necessary for toxicity to occur.

How to Fix Nitrogen Toxicity in Plants

Nitrogen Toxicity Cannabis
Nitrogen toxicity in a flowering cannabis plant.

Using sawdust as a mulch will help decrease the amount of nitrogen contained in the soil. Nitrogen toxicity can be corrected by:

  • Flushing the growing medium with pure water or a flushing agent
  • Correcting the pH level
  • Making certain plants are not fed excess nitrogen
  • Removing excess nitrogen from the soil

The most important step is determining if the plant is affected by nitrogen toxicity as quickly as possible. The medium should be flushed as soon as the issue is identified. Providing plants with fresh water will eliminate all excess nutrients present in the growing medium. The plants are then able to recover as the nutrients remaining are absorbed.

A flushing agent containing a specialized mixture can be used successfully as a flushing agent. Pure water is usually the most effective. Once the issue has been resolved, plants should resume the regular schedule for nutrient feedings. Sometimes, the issue is caused by too much nitrogen within the soil. The best way to treat this is by planting something the nitrogen in the soil will bind to.

How Long Does It Take for a Plant to Recover from Nitrogen Toxicity?

In most instances, excess nitrogen can be treated in the growing medium or removed from the soil in approximately five to seven days.


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