Iron deficiency in marijuana plants

Iron may just be a trace nutrient to the marijuana plants but a lack of it can lead to serious problems. In fact, it is one of the most common mineral deficiencies found in growing cannabis.

Why is iron important for weed plants?

What makes iron a crucial element is its role in the formation of chlorophyll. Essentially, this green pigment absorbs light, and together with carbon dioxide, converts it to plant food. Add to that, this element aids the uptake of nitrogen which triggers the rapid growth of leaves. Hence, not having enough iron compromises the plant’s ability to store energy and grow.

As a result, the plant becomes weak and malnourished which often leads to stunted growth and susceptibility to diseases. Ultimately, if nothing is done, this condition affects the yield and quality of the buds. Fortunately, there are many things we can do to stop this before it becomes severe.

Download my free Grow Bible to learn more about iron deficiency in cannabis.

In this article, we will cover all there is we need to know about this problem including its causes and treatment. But most importantly, we will learn to properly diagnose it so we can immediately fix it. Through this information, we can easily manage the issue before it gets out of hand.

Iron deficiency in marijuana plants

To grow healthy cannabis, it is vital for the plants to get all the nutrients they need at the right amount. In iron deficiency, the plants suffer from a host of problems that could be tricky to identify and treat. Hence, growers must learn how to tell if this condition is affecting their crop.


The biggest challenge with this problem is that it can be tricky to correctly identify. As such, growers commonly confuse a lack of iron to other mineral problems such manganese, zinc, and nitrogen deficiencies. To avoid this mistake, learn the most common symptoms of a plant that craves iron.

Early signs

Early signs iron deficiency-marijuana plant

The earliest sign of iron deficiency in plants is chlorosis in which the young leaves turn pale yellow but the veins remain green. Left untreated, it later works down and inward to the older leaves.

To differentiate it from other nutrient problems, determine which part of the foliage turns yellow first. Again, a lack of iron first affects the newest and freshest growth which is on the top part of the plant. Whereas other mineral deficiencies target the leaves on the middle part or base of the plant.

Late signs

Late Signs

As the condition progresses, the pale-yellow color of young leaves will get brighter and spread on the whole leaf. Luckily, iron deficiency spreads very slowly. Hence, there is ample time to make the right diagnosis and provide the remedy.

Also read “Nutrient deficiencies in marijuana plants

However, if left to continue, the yellowing will occur in every new leaf which will give the plant no chance to manufacture enough food. Ultimately, the leaves will drop and the plant will stop growing. Expect to see minimal bud sites as well.


To effectively treat the affected plants, we must first learn the root of the problem. By doing so, we not only get ideas on how to solve it, we also learn how to prevent it. Below are some of the most common reasons for iron deficiency in the marijuana crop.

Bad soil drainage

Bad soil drainage

Growers who like to use soil as the grow medium should make sure that it has a good drainage. Otherwise, the water will pool and make the soil compact and choke the roots. This makes it difficult for the plant to absorb iron which is naturally present in soil but only in minute amounts.

Thus, when choosing a soil, it is best to avoid clay-based materials since this tends to hold water. Most growers use a potting mix since it drains well and has high-quality organic elements.

Excess of other minerals

Excess of other minerals

Most of the time, the problem can be due to the excess amount of other nutrients such as manganese, phosphorous, zinc, calcium, or copper. Too much of these minerals can build up and block the uptake of iron in the soil.

Hence, we must find a way to balance the number of nutrients and work hard to maintain them.

Imbalance in the pH Level

A neutral or alkaline pH level is the most common cause of iron deficiency in marijuana plants. Interestingly, this happens when we use too much fertilizers.

How to measure soil's pH And PPM for your marijuana grow

To promote the absorption of iron, keep the soil’s pH between 6.5 to 6.7 by using a pH meter. The good news is, most nutrients also become more available for the plants when we maintain this pH value.



Like the effects of poor soil drainage, an overabundance of water limits the root from taking up iron. Therefore, it is best to know the correct watering practice to avoid this problem.

Using Coco Coir

While iron deficiency in cannabis can occur in all grow medium, it occurs most frequently in coco coir.

iron deficiency occurs most frequently in coco coir

This is mostly because this medium lacks organic iron and naturally contains a high amount of salt, making iron less available for the roots.


After confirming the problem and finding out what causes it, we can now confidently save the crop. This involves applying the three basic ways that ensure a quick and effective treatment.

Using the correct nutrients and plant protector will get you a long way and your plants will have less chance of getting sick, in addition of being less vulnerable for pests and diseases.

To make sure other growers don’t have the problems a lot of starters experience, I have created multiple grow sets which features all you need in order to grow healthy plants from seed to harvest!

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Flush and add nutrients

Essentially, we want the grow medium to have the right pH that will promote the absorption of iron. In effect, this method provides the fastest recovery to malnourished plants.

Flush and add nutrients

To start, we must flush the grow medium using water that has a pH of 6. This cleansing process makes sure that there are no excess minerals that locks out iron.

The next step is to follow it up in the next watering with an all-around nutrient solution designed for marijuana. Furthermore, to avoid the development of another nutrient problem, we must regularly check the pH of the grow medium.

Spray with iron chelate

Applying iron chelate on the affected leaves helps them regain chlorophyll so they can turn green again. But this is only a temporary remedy for iron deficiency.

Spray with iron chelate

As such, it helps only the leaves that are present during the spraying. Thus, we need to repeat the application every time a new growth appears.

Use soil additives

There are many products that are excellent sources of iron while also stabilizing the pH level of the soil. Hence, it’s up to the grower to select which one is the most convenient and suitable. But before starting any treatment, it is vital to flush the grow medium first so that it can facilitate iron absorption.


Adding compost decreases the pH value by 0.1 to 0.2. This helps stabilize the soil while also enriching it with iron. In addition, it also improves the drainage, helping the soil to readily take up trace minerals. To use, apply 3 to 4 inches of compost on the soil and work it up to 6 to 12 inches deep.

Elemental sulfur

It usually takes months to see the positive effects of elemental sulfur but it is worth it. As such, it provides the longest-lasting cure for the problem, lowering the pH and making iron more readily available to the plants.

Elemental Sulfur

To get the best results, work the sulfur 6 inches into the soil about a year before planting. This serves as the perfect prevention of iron deficiency in marijuana plants.


Another way to lower the pH level and make iron more accessible is to use nitrogen fertilizers. The ones that contain ammonium sulfate or urea work wonders in the soil. However, be careful to give only the amount that is recommended for the plant. For the sake of the plants, we want to avoid nutrient excess at all costs.

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Immediate treatment is key to fixing the problem

As with all other nutrient problems, the only way to save the plant is by acting fast. While iron deficiency tends to occur gradually, it can spread and wreak havoc on the plant’s health. Moreover, a quick recovery is crucial for a perfect harvest.

As growers, our role is to monitor the nutrient status of the crop and make sure that they are in their optimal condition. Thus, having the patience to do this as well as the skills to spot the first sign of trouble can be very useful. Equally important is knowing what to do when such problem arises.

By learning all the information on iron deficiency, we increase our ability to take care of the plants. As a result, our crop flourishes and we have the guarantee of harvesting enjoyable buds.

FAQs about iron deficiency in cannabis plants

What are some common signs of iron deficiency in marijuana plants?

The most common sign you will notice in your plant is the yellowing of leaves. Eventually, the leaves will drop and the plant will stop growing. You’ll see minimal bud sites as well.

How can you treat iron deficiency in cannabis?

Flushing and adding nutrients, spraying with iron chelate and using soil additives are some ways to treat iron deficiency in marijuana plants.

Practice and learning are all you need to become an expert marijuana grower. Get started with my blog.

Have you experienced iron deficiency in your marijuana plants? Please leave your comments below.

Happy growing!


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Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

16 comments on “Iron deficiency in marijuana plants”

  1. Hi my name is johnathan williams and i am having trouble iding the problem i have a female she is big one but but her some of her leaves even thouh they are new growth they are strarting to dry out and curl up .sime leaves are showing some brown spots on on them. Help dont want to lose her so if you have any idea what i need to do would send you pick if i could aany help would be greatly accepted thank you

  2. I’m trying to obtain a copy of your free download
    of “Marijuana Grow Bible,” but it’s not going through.

  3. EDDHA Iron Chelate versus EDTA Iron chelate…. what is the difference?
    EDTA Iron fails when the pH exceeds 6.8. EDDHA remains available from a pH of 4.8 to 10.5
    EDTA is often found in blends like 20-20-20 and remains availble for 3-10 days. EDDHA Iron remains available for 3-5 months. The EDDHA Iron molecule is significantly smaller than EDTA Iron… so it moves into the plant via mass flow.
    When growers move from the Veg Stage to the Bud production stage they often will stop using 20-20-20 and by default, the EDTA Iron is gone within 3-7 days. By the time they reach harvest the plant is very yellow. If you want to see dark green foliage all the way thru harvest without a flush of growth, consider EDDHA Iron.
    Consider the cosmetics too. I have strawberry growers who use EDDHA Iron for the purpose of making the calyx and stems dark green. Buyers get turned on to the way the berry is presented. Same goes for Cannabis Buds.
    Nabta manufactures water soluble fertilizer, chelates and humic acid. Nabta sol EDDHA 6% Iron chelate is ground down to a very fine powder and can be applied as a drip/drench or as a foliar application. The only cautions are not to apply with Calcium… and do not apply as a foliar during periods of bright sunlight.