severe iron deficiency cannabis

Iron Deficiency In Cannabis Plants

Published : Aug 9, 2017
Categories : Cannabis cultivation

Have you ever gotten, or currently have, yellow leaves in your cannabis plant? It could be an iron deficiency – a problem that is too often overlooked and can kill your crop.

Just like you and I, all living things need a very specific set of conditions to survive. But survival is not the only factor to take into account when growing cannabis. If you want good quality buds don’t expect to only water your plant every day and collect the yield when it’s done. This is so important that we’re writing an article on just one minuscule problem in the marijuana growing process: Iron Deficiency.


Nutrition is an extremely important step that should not be overlooked. Within the plant’s nutrients are the essential minerals that keep your plant healthy. Iron plays an important role during photosynthesis, contributing for both pigmentation and leaf respiration of your plant. It is also a key element in triggering the formation of chlorophyll, as enzymes require it to function properly. It’s particularly vital for younger, still growing tissues in marijuana.

Iron deficiency is a consequence of not enough supply of iron to the plant. Iron excess is also a problem, but we’ll be focusing on the one mentioned in the title. These two conditions are visually expressed in different ways. The major thing to look out for is the change in colour to yellow of your plant’s leaves. This will happen mostly with younger, inner leaves. Iron nutrient deficiency can appear very similar to a magnesium shortage. The key difference is that while iron deficiency will affect new leaves, the magnesium shortage affects older and lower ones. These leaves might even turn white. Most often you will see symptoms toward the top of the newer foliage. With this specific deficiency, affected parts of the plant have the ability to eventually return to their healthy colour. In most nutrient deficiencies, yellow leaves won’t really turn green every again.


An iron deficiency is usually caused by problems with pH, though sometimes it can be triggered by a stressful environment. If it’s the latter, it may clear up on its own after the period of stress is over. Make sure you’re doing everything correctly and that you’re not giving your plant too much of anything.

Iron is always available in the soil as long as it’s well-cared-for. Most of the times, the problem is that the plant can’t access the essential nutrients due to lock-out conditions.

One way you might stimulate lock-out conditions is by over watering your plant and/or not draining it properly. This will keep the roots under a lot of stress and prevent them from collecting the iron you want. Younger roots absorb the iron much better than older ones. Having a clear and cared root system is necessary to get an effective uptake.

There are other reasons a plant may not be able to absorb iron efficiently. High levels of carbonates, low temperatures or excess of phosphorus may cause a nutrient lockout.

This deficiency spreads slowly through the plant. Iron’s mobility is slow and this will give you a chance for recovery – if you act quickly. Remember that plants with strong genetics have, consequently, stronger immunities against adverse conditions. Make sure to buy your seeds from a trusted source.


It’s possible that an iron deficiency may just be the result of overwatering. If you’re growing in soil, let the medium dry out, then flush it with slightly acidic water with a pH of 6.0–7.0. Iron tends to get locked out with more alkaline water (pH over 7.0). If you’re growing hydroponically, you should flush your system with water that is even more acidic, shooting for a pH of 5.5–6.5. This should be your first step when spotting those yellow leaves.


If you still witness the same condition happening, try out an iron, calcium and magnesium supplement. Cannabis loves calcium and magnesium as these work beautifully with iron. A supplement of this kind can also help prevent such a deficiency. Even if your plant is not showing symptoms, you can never be too careful. Just make sure you’re not stressing it with nutrients as it might work in the opposite way.

If everything goes well, after a week or so, you’ll start to see a difference. Old leaves might not fully recover. These might keep their yellowish or already white colour; they’ll eventually fall out as they’re probably dead. Watch for the newly born ones. If these appear to be growing healthy, you’ve solved the problem.

We hope this helped you solve a current problem or prevent a future one. Prevention is always better than treatment and keeping yourself informed is half the battle. Be sure to keep up with the latest news in cannabis growth and to follow current literature and research on your favourite plant. There is still a lot to discover about it and there will always be problems to overcome. At least now, you can cross iron deficiency from your worries list because. Good luck with your crop and most importantly, have a good harvest.

A Guide On Properly Drying And Curing Your Cannabis Flower

Find out how to cure and prevent iron deficiency in your cannabis plant, a problem that is too often overlooked and can kill your crop.

Iron Deficiency

by Nebula Haze & Sirius Fourside

Problem: A cannabis iron deficiency is usually seen first on bright yellow new leaves, and the symptoms of a cannabis iron deficiency can sometimes appear alongside other cannabis nutrient problems or deficiencies. An iron deficiency is usually caused by problems with pH, though sometimes a cannabis iron deficiency can be triggered by a stressful environment and may clear up on its own after the period of stress is over.

The main symptoms of a cannabis iron deficiency are:

  • Newest leaves are completely yellow when they first grow in
  • The bright yellow (almost white looking) color on new growth is the signature sign of an iron deficiency.
  • Sometimes the affected yellow leaves are so damaged they’re beyond recovery. Other times the yellow parts of the leaves may begin to turn green as the plant continues to grow, starting from the tips and moving in toward the base of each leaf
  • Eventually an entire leaf can become green and relatively healthy looking, even though it started out completely yellow from an iron deficiency. The ability of yellow leaves to eventually turn green is another signature of an iron deficiency, because for most other nutrient deficiencies any yellow leaves can’t truly turn green again.

A cannabis iron nutrient deficiency can look similar to a magnesium deficiency, but an iron deficiency will affect newer/upper/inner leaves, where a magnesium deficiency affects older/lower leaves.

The following severe iron deficiency was actually caused by an outdoor grower using too much pure chicken manure as a fertilizer. Any time you use manure to fertilize your plants, remember a little bit goes a long way! Chicken manure tends to raise the pH of soil, which is one of the prime triggers of an iron deficiency. In addition to changing the pH, the high level of nutrients contained in chicken manure may have interfered with iron uptake by the roots, causing further iron lock-out.

Immediately after adding chicken manure and watering, the plant started producing bright yellow, almost white leaves that immediately dried up and died from the damage. Even though this plant was showing the signs of an iron deficiency, the iron was available in the soil – the problem was that the plant just couldn’t get access to the nutrients due to nutrient lock-out conditions. In this case, grower needs to dig up the manure (since that is the real cause of this problem) & replant with good soil.

Solution For Cannabis Iron Deficiency

Note: Sometimes a cannabis iron deficiency (like all nutrient deficiencies) can be triggered by stressful conditions, and the plant may recover on its own after the period of stress is over.

1.) Adjust pH to Correct Range

Easily the most common reason growers will see an iron deficiency is if the pH at the roots is too high. Iron tends to get locked at at higher pH levels, especially when the pH is above 7.0, and iron deficiencies are more commonly seen in soil or coco coir than in hydro.

If you suspect your growing cannabis plant has a iron deficiency due to too-high pH, flush your system with clean, pH’d water. This will remove any nutrient salts that may be affecting the uptake of iron and help restore pH to the proper levels..

  • In soil, iron is best absorbed by the roots in the 6.0 – 6.5 pH range (although it’s generally recommended for soil growers to keep pH in the 6.0-7.0 range, iron tends to get locked out when the pH is higher, especially above 7.0)
  • In coco coir or hydro, iron is best absorbed by the roots in the 5.5 – 6.5 pH range

2.) Give the Right Nutrients

The truth is, most cannabis growers don’t need to add more iron in response to an iron deficiency!

In fact, most growers have actually already given plenty of iron to their cannabis plants since it is found abundantly in most tap water. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to worry about adding more iron.

Iron deficiency symptoms caused by true lack of iron are more likely to appear when a grower is using heavily filtered or reverse osmisis (RO) water to feed plants since any iron has been removed. There are other nutrient problems that can trigger the symptoms of an iron deficiency, for example problems with with calcium and magnesium, or an excess of copper can all lead to symptoms of an cannabis iron deficiency.

If you suspect you have a iron deficiency even though the pH is correct, or if you believe your system is truly lacking in iron, you may want to consider flushing your system with clean, pH’d water (if on schedule, you can do this alongside a dose of your regular nutrients) and add a supplement that contains Iron, Calcium and Magnesium.

Cannabis loves Calcium and Magnesium, and they work hand and hand with Iron. A Calcium-Magnesium supplement (often called “Cal-Mag” even though they also include iron) can help prevent all of these deficiencies from appearing.

Cal-Mag products are suitable for Hydro, Coco Coir and Soil (not organic, though). This may be a great choice because it also contains extra calcium and magnesium, which are deficiencies that are relatively common for cannabis, and often happen alongside an iron deficiency.

CaliMagic by General Hydroponics is the calcium, magnesium, and iron plant nutrient supplement that we use, though pretty much all other Cal-Mag products will work just as well for growing cannabis.

3.) Take Good Care of the Roots

Iron deficiencies can show up with the plant is having root problems or if the plant is overwatered, even if the pH is right and the iron is there. Proper watering practices help plants grow healthy and avoid a host of problems!

4.) Watch for Recovery

After going through all the above steps, watch to make sure that the iron deficiency starts to clear up within a week or so (try to be patient since iron moves relatively slowly through the plant). The yellow leaves from before may not recover completely, especially if there was a lot of damage, but when new growth is coming in green, you know you’re good to go!

If you cannot get rid of a cannabis iron deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems

Plant Symptoms

  • Bronze or brown patches
  • Brown or slimy roots
  • Brown or yellow leaf tips/edges
  • Buds dying
  • Buds look odd
  • Bugs are visible
  • Curling or clawing leaves
  • Dark leaves
  • Drooping plant
  • Holes in leaves
  • Mold or powder
  • Pink or purple on leaves
  • Red stems
  • Shiny or smooth leaves
  • Spots or markings
  • Twisted growth
  • Webbing
  • Wilting leaves
  • Yellow between leaf veins
  • Yellow leaves

This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.

Problem: A cannabis iron deficiency causes bright yellow leaves on new growth. This deficiency is usually caused by problems with pH.