Iron Deficiency in Marijuana

The most obvious symptom of an iron deficiency is caused by a lack of chlorophyll, you will see it as a yellowing of the leaf while the veins remain green.

This chlorosis is more noticeable in new shoots. If the deficiency is not solved, the leaves will begin to discolor completely and will go through the plant as the iron deficiency becomes more severe.

It is often accompanied by other deficiencies, because pH errors, high root salinity, or low temperatures are the most common causes of iron deficiency.

The iron your plant uses to help with the development of new and young tissues, is an important component during photosynthesis and the production of chlorophyll. If your plant lacks iron, you have problems.

Colors and Symptoms

In New Leaves and Buds

Leaf ColorSymptoms
Strong yellow while veins stay greenGrowth and development slows down
Discoloration to the point of turning whiteNew small or stunted shoots
Tips stay greenLeaves develop necrosis spots and die

Identifying this deficiency is simple, first the upper leaves of your plant will begin to lose color between the veins, turning a strong yellow. Then the newborn leaves will be completely yellow or almost white due to the lack of chlorophyll. The veins of the larger leaves will stay green.

If you let this advance the larger leaves will begin to show this chlorosis, which will progress through the leaf until it is completely covered. The new shoots will be damaged and stop growing, in some cases the shoots will be so damaged that they will no longer grow.

In severe deficiency the leaves will be white, discolored. At this point the correct development of the plant is seriously compromised, and you should fix it as soon as possible.

At other times you could see that the deficiency is removed after a few days, leaves that were completely yellow begin to return to their original green. This does not happen with most deficiencies, so this symptom confirms that you were facing a lack of iron.

It can be mistaken for a magnesium deficiency. The difference is that while iron deficiency manifests itself in all shoots and tall leaves, it then descends through the plant, while chlorosis due to lack of magnesium shows its symptoms in older, lower leaves.

Iron Deficiency Pictures

How to Solve an Iron Deficiency

Causes, what are we going to fix?

It is very rare that you have a lack of iron, it is most likely that your plant cannot absorb iron from the soil.

(Pipe water is loaded with iron and is not a commonly missing element.)

To solve a deficiency you must know your plants very well, know what the soil is like, the water with which you water and how much you water. Know what fertilizers you have added and check them for insects and pests.

Since in most cases, when there is a lack of iron, the problem is usually another.

PH error and excess salts

Iron becomes available to the plant when the pH of the substrate stays below 7. The irrigation water or fertilizers that you have added to the substrate may have generated a variation in pH and is causing a blockage.

Try lowering the pH to about 6.5 to enable iron absorption and fix the deficiency.

You may have a blockage due to excess salts if you have been fertilizing your plant, especially if you have used strong fertilizers such as guano or chemical fertilizer.

One way to fix this is to wash the substrate / roots with water (which you have previously left to stand uncovered for at least 24 hours). The water will remove excess salts and fertilizer, returning the pH to normal.

You can also view this guide with methods of varying the pH of your substrate.


If you know that your plant may have suffered from stress in the last days, this may be the cause of iron deficiency. Too many hours of darkness, transplants, excessive or poorly done pruning, too much heat can generate enough stress to cause it.

If this is the case, continue caring for her and the gap should be fixed on your own after a few days.

Too cold

Temperature changes are not favorable for marijuana plants, maintaining a stable temperature both in the growing environment and in the root system is essential.

Below 20ºC the leaves will begin to show problems, especially if this problem continues over time.

If you grow outdoors you can consider raising a greenhouse around it, or maybe just cover it with a tarp at night. If you have pots, just bring them into the house when the temperature drops.

If you grow indoors you can try a carbon dioxide (CO2) generator to improve the temperature, another option is also valid electric blankets, be careful to use them with a timer to avoid getting overheated.

This extensive Alchimiaweb guide explains everything about the cold in marijuana.

Excess Irrigation and Bad Drainage

Over watering or poor drainage can cause various root problems and even lead to fungal growth. And this may be causing the blockage that does not allow the absorption of iron.

Cannabis is a hardy plant but it also has limits. Make sure your culture medium has good drainage. If you have containers they should have enough holes at the bottom, and the water should come out of them at least a little every time you water.

I leave you this Sensi Seeds watering guide in case you think this may be the cause.

Excess Phosphorus (P)

This excess is a common cause of an iron deficiency. If you fertilize your crop, especially if you do it with strong fertilizers like wood ash, you may be in this situation.

Too much phosphorus blocks the absorption of various nutrients including iron, calcium, magnesium, zinc.

In this case you can perform a root wash as mentioned in the section “Error pH and excess salts”.

Adding Fertilizers

As you have seen, it is likely that you do not need to add iron to your soil and that the cause of the lack is another. If you have a good substrate and fertilize normally, don’t worry that iron is missing.

If you really believe that none of the above is the cause, but that you really need to give your plants iron, you can buy a fertilizer. Calcium and Magnesium supplements that are accompanied by good amounts of iron are ideal for these cases, since they are nutrients that are related to each other.

Thank you for reading

As you can see, most of these causes are based on poor care of the roots. It is the newer roots that better absorb iron, so it is important that you keep the root system healthy and in good condition.

After carrying out any of these solutions in 1 week or less, you will begin to see how the leaves improve and recover their color, and the growth of shoots resumes its original rhythm.

It is possible that some very stunted sheets cannot be recovered, in this case it will be best to cut them, since iron is an ‘immobile’ element and these sheets will have no solution. But you will see that the new growths will come out green and alive.

I hope you can solve your iron deficiency without major problems. I will be publishing more guides on nutrient deficiencies and other steps of growing marijuana. I would love to be able to notify you when I publish a new one, if you want you can sign up to the mailing list below.

Santiago @ Dr. Cannabis
Santiago @ Dr. Cannabis
I'm here to help out marijuana growers have a greater experience with their plants, and not loose their mind over the many problems and situations that often arise during the different stages of cannabis growth.
Share on facebook
Share on twitter
Share on pinterest
Share on email
Share on print

Leave a Reply

Your email address will not be published. Required fields are marked *