Deficiency and excess of Iron in cannabis plants

In the scenario of nutrition in agriculture, where each element plays a crucial role in the life of plants, iron is an essential actor in the development and vitality of plants, playing a fundamental role in processes as important as photosynthesis, the formation of chlorophyll, or resistance to environmental stress.

Today we invite you to discover the relationship between this element and your plants, as well as what you should do if they show any symptoms of a deficiency or excess of this important micronutrient.

 Iron is an important micronutrient in the diet of all types of plants, and cannabis is no exception (Image: Indorgro)
 Iron is an important micronutrient in the diet of all types of plants, and cannabis is no exception (Image: Indorgro)

Iron in cannabis cultivation

Iron is not a mobile element, and although it is not part of chlorophyll, it does contribute to the pigmentation and respiration of the leaves of marijuana plants. In addition, it also interacts directly with the creation of enzymes. The plant can assimilate it in the form of ferric ion (Fe++) although it can also be absorbed in organic form.

Plants use different and varied mechanisms to absorb the iron that is in the substrate but that is presented in a format that is difficult for them to assimilate. The chelation mechanism, which is based on the creation of siderophores that come into contact with different bacteria, will make iron more usable for marijuana plants.

Another mechanism that plants use is to expel substances that reduce the pH of the substrate around their roots. It should be noted that younger roots can absorb iron better, so it will be very necessary to maintain a clean and cared-for root system for iron absorption to be effective.

As we have already mentioned, iron comes in various formats, with chelated iron being the one with the best absorption by plants. In this case, it should be noted that there are different types of chelates, each with greater resistance and stability depending on the conditions in which the substrate is found.

These chelates stabilize metal ions, improving their resistance to iron oxidation and helping them to not precipitate so easily. It should be said, however, that chelates can compete with other ions of other elements such as calcium and magnesium, which will displace iron ions.

Types of chelates:

  • Fe-EDTA: This chelate is suitable for substrates with a pH less than 6.0. With a pH above 6.5, half of the Iron will not be available, so it will not be very functional.
  • Fe-DTPA: This chelate is known to remain stable at pH 7.0 and not displace iron with calcium.
  • Fe-EDDHA: This chelate remains stable up to pH 11.0 although it must be said that it is also the most expensive.

 Beginning of an Iron deficiency in cannabis
 Beginning of an Iron deficiency in cannabis

Iron deficiency in cannabis cultivation

In crops, deficiencies of this element are usually preceded by a pH value in the substrate greater than 7.0, in which the plant cannot absorb this element through its roots. Keep in mind that it cannot be absorbed in very alkaline or very calcareous soils either.

There are other reasons why iron stops being assimilated by the plant even when it is present in the substrate. These cases can be such as high levels of carbonates, high salinity, constant humidity, low temperatures, or excess of other microelements that cause their deficiency.

In this case, the youngest leaves, those at the highest part of the plant, will suffer iron chlorosis, keeping the veins green. If you do not act accordingly, the leaves will discolor, leaving the veins green.

 Advancement of an Iron deficiency in cannabis
 Advancement of an Iron deficiency in cannabis

Summary of the causes that cause iron deficiency:

  • Lack of iron in the soil is possible although rare
  • Immobilization of iron in an alkaline substrate can be caused by an excess of calcium or bicarbonate in the nutrient solution
  • The presence of certain organisms that transform iron into ferrous oxide, which is not absorbable by plants.
  • Interaction with other cations caused by an excess of manganese, copper, zinc… (heavy metals)
  • Weak root system due to poor drainage, low temperatures, lack of oxygenation, etc.
  • Excess light intensity

How to solve an iron deficiency in plants:

  • Reduce the alkalinity of the substrate, providing sulfur, manure, and organic fertilizers along with fertilizers that acidify the substrate
  • Provide iron chelates to the plant for rapid absorption in an optimal pH range
  • Foliar dosage with iron sulfate to solve small deficiencies

 Advanced phase of iron deficiency
 Advanced phase of iron deficiency

Excess iron in cannabis cultivation

Excess iron in plants can lead to specific symptoms. Here are some common signs of too much iron:

  • Chlorosis and Yellowing of Leaves: Although iron is essential for the formation of chlorophyll, an excess can cause chlorosis, manifesting as yellowing of the leaves, especially between the veins.
  • Root Damage: Excess iron in the soil can damage roots, affecting their ability to absorb nutrients and water.
  • Reduced Growth: Excess iron can interfere with the absorption of other essential nutrients, which can result in decreased plant growth.
  • Iron Accumulation on Leaves: There may be visible iron accumulation on the leaves, often as brown or red spots.
  • Increased Susceptibility to Disease: Excess iron can make plants more susceptible to certain pests and diseases.

It is very important to monitor the health of the plants and adjust fertilizer doses as necessary to avoid problems associated with excess nutrients. Regular observation of the condition of the plants and the implementation of corrective measures will help maintain an optimal nutritional balance in your crop.

As always, if you have overfertilization problems, it is best to wash the roots with enzymes by watering with three times the amount of water in the volume of the pot, and then use a light fertilizer with the pH corresponding to the life stage of the plant.

Happy harvest!

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Deficiency and excess of Iron in cannabis plants” (11)


Jonathon 2023-01-13
My plants showed whitening,an iron deficiency. I dug a little iron sulphate into the soil( outdoor plants) now they're showing signs of too much iron ,( colour change etc) I amnew to this so HELP PLEASE! I'm in Australia

Alchimia Staff

Dani Alchimia 2023-01-26
Hi Jonathon, If you can recover some of the iron sulphate and then add some new substrate if needed, you'd make sure that no more iron would be released into the soil. Normally, when dealing with nutrient excesses, you water thoroughly with just water and enzymes (you can do it a couple of times, just make sure that you don't overwater the plant. Water once, wait for a few days, and water again). Hope it helped!


Bagmorad 2021-12-11
Hello, thank you very much for your guidance

Alchimia Staff

Tim Alchimia 2021-12-13
It's our pleasure, thanks for your kind words. we're happy to have been helpful. Best wishes and happy growing!


Jack 2020-08-03
I'd like to post a picture of my plant as well as a picture of the leaf tissue sample results showing excessive Iron. Albeit not ironclad conclusive (pun intended), a sample to be discussed.

Alchimia Staff

Tim Alchimia 2020-08-04
Hi Jack, thanks for your response. Please send the files to me at I'm very interested to have a look! All the best.


Jack 2020-07-23
This has nothing to do with with excess iron, the whole article is about iron deficiency.

Alchimia Staff

Tim Alchimia 2020-07-28
Hi Jack, thanks for your comment. That's a fair point, but in reality, it's because Iron toxicity or excess isn't something that cannabis plants have been observed to suffer from. If you have any information that contradicts this we'd love to see it and make the necessary corrections to our article. Thanks again, best wishes and happy growing!


Jack.bren 2020-06-03
I have hemachromatosis and can have no products with iron. Could I smoke it for hashimotto leg pains

Alchimia Staff

Tim Alchimia 2020-06-03
Hi Jack, thanks for your comment and question. I'm unclear on the interaction between cannabis use and iron levels in the body. I've searched online and can find no clear link, so I'd assume there's no serious problem that could arise from smoking it, although you should talk to your doctor about it if you have any other conditions. From what I've read, it appears that THC-rich cannabis could have a very beneficial effect for sufferers of Hashimoto's disease, because of its immuno-suppressant and anti-inflammatory effects as well as its pain-relieving qualities. However, you'll need to check with your doctor whether you have TH-1 or TH-2 dominant Hashimoto's. THC can very beneficial for TH-1 type Hashimoto's, while it might even be harmful to TH-2 sufferers. The effects of CBD aren't clear, but it may have the potential to worsen the condition, so it's not recommended at the moment. I really hope that helps you out, best wishes.


Maureen MacDowell 2018-06-07
How much iron is the in marjuana itself .I have hemacromatosis, an iron overload ,is it safe to vap?

Alchimia Staff

Tim Alchimia 2018-06-08
Hi Maureen, thanks for your question. I think you'll be fine vaporising, any iron present in the plant would only be absorbed if you ate it. I hope that's reassured you. All the best and happy vaping!


sean don 2018-01-01
yo yo yo

Alchimia Staff

Tim Alchimia 2018-01-02
Ho Ho Ho! Happy New Year!


Jesse 2017-12-30
Excellent article. Extremely helpful. Thank you very much


Adel newier Is an Alchimia client 2016-06-20
Your probleem diagnosis is better than canna and more other articles on the internet. Thank you alot, hope you make more series of those articles and maybe a forum to help growers fixing thier probleems. Thanks alot again..

Alchimia Staff

Dani Alchimia 2016-06-20
Hi Adel, We are glad you liked our Growing Guide, we are always trying to improve it! ;) All the best!


Ben hope 2016-05-30
Thanks a lot of this exzellent nutrient deficiencies &excesses guide!

Alchimia Staff

Dani Alchimia 2016-06-07
Hi Ben, Thanks for your kind comment, we're glad it helped! All the best!


Shane 2015-12-11
Great article! Thanks for the info

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