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How to Fix Cannabis Iron Deficiency

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Are your weed crops losing their vibrant color? If your foliage looks pale and limp, it might be due to a cannabis iron deficiency. Fortunately, you can treat this condition, and your plants can still produce a decent harvest if you act swiftly

Below, we explain why iron is essential to the development of your weed. We highlight the dangers of a deficiency and what symptoms to look out for. We also look at some of the causes so you can eliminate any future issues. 

Let's kick things off by looking at what exactly an iron deficiency in cannabis is.

Discolored cannabis leaves
Discolored cannabis leaves

What does iron do for plants?

Cannabis crops only require trace amounts of iron, but the nutrient's roles are vital. These include:

  • Produces chlorophyll 
  • Regulates the plant’s metabolism 
  • Aids the respiration process
  • Helps essential nutrients through the plant’s circulatory system
  • Enhances nutrient absorption during the vegetative stage

If there’s a cannabis iron deficiency, it's a catalyst for problems on a larger scale. The plant can't perform photosynthesis properly, and it develops poorly. Any buds from these crops will lack potency and maybe even flavor. 

What is iron deficiency?

Iron is a micronutrient and plays an essential role in cannabis plant health. When there’s a lack of the nute, and you suffer a marijuana iron deficiency, the young leaves start losing color first. It then spreads to the rest of the foliage, making it look pale and sickly.

If the issue is left unattended, the crops get weak, and they grow slower. The malnourished weed plant then produces poor quality buds, and the yield is typically low too. There’s a variety of causes and measures you can put into place to prevent this problem.

Iron deficiency symptoms
Iron deficiency symptoms

What causes cannabis iron deficiency?

Cannabis iron deficiency is a common occurrence as there are multiple causes. Some include

  • Grow medium
  • Imbalance pH
  • Other minerals
  • Bad drainage
  • Overwatering
  • Plant stress

Grow medium 

The optimal conditions for iron are more apparent in soil than in other mediums. Growers who favor coco coir need to be cautious as it lacks this nutrient and contains lots of salt. The excess salt increases the risk of iron deficiency in cannabis. 

Imbalance pH

If your crop’s pH levels are off, it can lead to various nutrient problems. Marijuana plants flourish at a pH range of 6.5-6.7 in soil. When the medium is too alkaline, a cannabis iron deficiency occurs. 

Growers who use too much fertilizer often have this problem. You can check your levels with a pH meter and take swift action to remedy an imbalance.

Other minerals

Nutrients exist in a delicate balance. Too much of one causes the reduction of another. When there’s an excess of calcium, zinc, copper, phosphorus, or manganese, a marijuana iron deficiency occurs. 

Bad drainage

If you opt to grow in soil, bad drainage might cause issues with nutrient absorption. Clay-based substrates typically hold more water and cause it to pool. The accumulation of liquid makes the soil compact and chokes the roots.

Poor drainage can lead to an iron deficiency in your cannabis. Potting mixes with organic elements don’t usually cause this problem. 


Too much of anything can be damaging to your crops. Water is no exception. As with bad drainage, when you add too much moisture to the soil, you block the roots from absorbing nutrients properly.

Develop a healthy watering schedule to prevent a cannabis iron deficiency. 

Watering weed
Watering weed

Plant stress

When weed plants suffer stress from transplanting, pruning, or temperature fluctuations, it triggers problems. Allowing your crops too many hours in the dark also stresses them. One of the consequences is a marijuana iron deficiency. 

Signs of iron deficiency in weed plants

Like with most nutrient problems, a cannabis iron deficiency isn’t always easy to detect. Fortunately, your plants will exhibit several signs indicating an issue.

Chlorosis in new leaves

Chlorosis is one of the earliest symptoms of nutrient deficiency. Starting at the base, the color of young leaves starts fading. New growth is a pale yellow due to the lack of chlorophyll. 

While these signs are associated with other plant problems, the issue occurs in the youngest leaves in crops with a marijuana iron deficiency. 

If another nutrient is responsible for the loss of color, the changes happen in the middle and lower foliage. This condition spreads throughout the leaves as it progresses.


The color change gets accompanied by weak, damaged shoots that grow rather slowly. The speed of an iron deficiency in cannabis is fortunately staggered, allowing you time to repair your crops. 

Should the condition continue unchecked, necrosis spots develop, and the leaves can die. In some cases, these damaged patches occur on foliage with green tips. 

How to fix iron deficiency in marijuana plants

Fortunately, cannabis iron deficiency progresses slowly. The sooner you notice it and take action, the faster your plant will heal. Even if you take action later, you can save your plant but may compromise on bud quality. 

Some ways to remedy the situation include: 

  • Pruning
  • Iron Chelate 
  • Compost 
  • Elemental sulfur
  • Fertilizer 
  • Flushing


If the cannabis iron deficiency is still in the early stages, you might be able to get away with pruning affected foliage as a temporary measure. Trimming pale leaves can buy you some time while you decide how you're going to fix the cause. 

Be careful not to over-prune. Remove only the affected areas and foliage to encourage further growth. If the damaged parts are excessive, you'll have to skip this option and take more serious measures.

Pruning weed
Pruning weed

Iron Chelate 

If most of the foliage has started turning yellow, another quick fix is spraying them with iron chelate. It helps the leaves develop chlorophyll, but it won’t solve marijuana iron deficiency. If you use this option, you’ll need to spray any new leaves once they develop.

The best action is to apply iron chelate to your crops and remedy the root cause of the problem. 


Most growers opt to purchase soil additives in conjunction with fixing the pH levels of the substrate. Utilizing compost lowers the pH by 0.1–0.2. It improves drainage and encourages the soil to absorb minerals more rapidly.

To effectively treat an iron deficiency in cannabis using this method, add 3–4 inches of compost to the soil. 

Elemental sulfur

Elemental sulfur is known to lower soil pH. The main drawback is that results take a long time to show. It makes iron easy to absorb and gets rid of the deficiency for a long time. It typically takes a couple of months to see the difference. 

If you want to use elemental sulfur as a preventative measure, mix it in the soil a year before planting. For best results, work it 6 inches deep and pair it with compost. 


Nitrogen fertilizers with ammonium sulfate combat iron deficiency in cannabis rather swiftly. You can also choose a product with urea. 

They lower the pH level and make iron accessible. Be careful not to overfeed with these products as excess nutrients are problematic too.


Flushing is the best way to promote a healthy balance of nutrients in your soil. When you have a marijuana iron deficiency, there are two ways to flush. 

Flush with dialed in pH

This method requires you to flush your medium with 6.0 pH level water. It gets rid of any excess nutrients and gives you a new base to start from. The second watering needs to include a nutrient solution of 6.5 pH. Your soils levels will balance.

Flush and improve supplements

Buying affordable fertilizers and substrates may seem like the smart financial option, but it can be the cause of your issue. After flushing your iron deficiency cannabis with clean water, supplement with cannabis-specific nutrients.

Switching brands might seem expensive, but in the long run, your crops flourish.

                          Symptom                             Solution 
Pale spots on new growthsPrune the damaged sections
Spray with iron chelate
Apply compost
Elemental sulfur
Loss of leaf color in most of the foliageSpray with iron chelate
Apply fertilizer
Necrosis spotsFlush 
Apply elemental sulfur
Dying or drooping leavesFlush 
Apply elemental sulfurIron chelate

If you know the cause of your cannabis iron deficiency, finding the appropriate solution is easier. 

                            Cause                          Treatment
Overwatering Stick to a strict watering schedule
Add holes to the containers
Flush and replant
Imbalance pHFlush 
Use elemental sulfur
Poor drainageCombine your medium with potting mix
Transplant into high-quality soil
Excess mineralsFlush 
Inadequate nutrients in the grow medium Maintain pH levels of 5.5–6.5
Ensure adequate drainage
Stress Maintain a strict water schedule
Develop a feeding schedule
Apply elemental sulfur
Healthy cannabis flowering
Healthy cannabis flowering

Ironing out the details

Iron is vital to the healthy development of your marijuana crops. It facilitates the absorption of other nutrients and the production of chlorophyll. When you have a cannabis iron deficiency, the leaves lose color, growth slows down, and you get a poor bud quality. 
Fixing the issue is fortunately possible. The faster you act, the lower your chances of long-term damage. Not sure this is the root of your problem? Check out our blog for other deficiency issues to get your harvest back on track.

About the author: Parker Curtis

Parker Curtis has around a decade of cannabis-growing experience, specialising in soil-less and hydro grows. He’s mastering outdoor, greenhouse, and indoor grows.

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