How to Fix Cannabis Iron Deficiency

Cannabis iron deficiency
October 22, 2021

Cough cough. Oh no! Your cannabis plants are turning yellow, and leaves are falling, but you have no clue what’s wrong. Could it be a cannabis iron deficiency? This issue is fairly common, especially with certain grow mediums. 

The good news is an iron deficiency in cannabis is easy to spot and simple to treat if you act fast. We’ve got all the answers you need, from how to spot the signs, ways to treat them, and what causes this deficiency dilemma. Let’s get started. 

What is iron deficiency?

An iron deficiency cannabis problem is the result of a lack of this crucial nutrient. It’s one of the most common nute deficiencies. Iron is essential for plants to grow strong, and a lack of it can severely stunt the height and appearance of your crop. 

Typically a cannabis iron deficiency is visible in the upper parts because it’s an immobile deficiency, showing on new growth. Iron isn’t one of the primary nutrients that cannabis plants need (nitrogen, phosphorus, potassium), but it’s vital for healthy functioning.

What does iron do for plants?

Iron plays several vital roles in nurturing weed plants. Some of its functions include: 

  • Forming chlorophyll, which converts light and carbon dioxide to plant food and adds green pigment to crops.
  • Increases the absorption of nitrogen—an essential cannabis nutrient. 
  • Regulates the plants’ metabolism. 
  • Essential for nutrient uptake during the vegetative phase. 
  • Helps carry essential cannabis nutrients through the circulatory system. 

This nute has some major functions, so it can severely stunt your greenery when there’s an iron deficiency in cannabis. Iron is a micronutrient with a big job—aiding the respiration process

Having substantial iron levels ensures that your plants get enough food, water, and air, plus it creates their beautiful green tone. 

What causes cannabis iron deficiency?

It’s important to know what causes a cannabis iron deficiency to treat it effectively. The signs may show in the yellowing leaves, but an iron deficiency is a root zone issue. Getting to the bottom of the problem helps to prevent nutrient loss and keeps plants feeding well. 

Here are some common causes of iron deficiency in weed plants:

Poor soil drainage 

Soil is an excellent growing medium— it’s inexpensive, organic, and works for most herbs. The downside is earth on its own can cause a buildup of water, which can choke the cannabis roots. Clogged roots find it difficult to absorb nutrients, causing a marijuana iron deficiency. 

Naturally, the soil has some iron content—but relying on that alone isn’t enough. To prevent iron deficiency cannabis issues, use a potting mix for soil to help drain excess water and avoid clay-based soil materials. 

Excess of other minerals

You can have too much of a good thing— that saying also applies to vitamins and minerals. An excess of nutes like manganese, phosphorus, copper, calcium, or zinc causes a cannabis iron deficiency. When these nutrients build up, they block the soil from absorbing iron

Imbalance in the pH level

An imbalanced pH level is the most common reason for an iron deficiency in cannabis. Ironically, too much fertilizer causes a neutral or alkaline pH, which stops the soil from absorbing iron.   

Keep the pH between 6.5–6.7 to boost the absorption of iron. Maintaining this value also makes nutrients easily available to the plants, which prevents a marijuana iron deficiency.


Many novice growers make the mistake of over-watering their flora, which leads to excess moisture at the roots preventing iron absorption. When the roots get blocked, it causes a cannabis iron deficiency. 

Of course, water is crucial as it acts as a carrier for nutrients and keeps plants cool. Knowing how much to use depends on plant size, temperature, soil type, strain, and other factors. Make sure you research the cultivar well before coming up with a watering schedule.

Using coco coir

All growing mediums can become plagued with iron deficiency cannabis problems, but it’s more common with coco coir. This medium is an excellent choice for many cannabis strains like Bubba Kush autoflower seeds. Coco coir doesn’t have organic iron, however, and the high salt content inhibits its absorption. 


If your plant has suffered stress, this could trigger a cannabis iron deficiency. It’s essential to follow a schedule for lighting, feeding, and watering. Potential stressors include:

  • Transplants
  • Excessive pruning
  • Extreme temperatures
  • Too many dark hours

Iron deficiency cannabis complications that are triggered by stress usually clear up on their own if you take good care of your plants. 

Marijuana iron deficiency symptoms 

A cannabis iron deficiency can be tricky to spot, and many growers confuse it for other problems. Let’s discuss the symptoms to look out for so you can spot iron deficiency problems.

Early warning signs

Typically the first sign of iron deficiency in cannabis is chlorosis, which turns the upper leaves a pale yellow. Other mineral deficiencies tend to affect the middle or base of the plant. When left untreated, the pale yellow travels downward, affecting the older leaves too. 

As the marijuana iron deficiency progresses, larger leaves develop interveinal chlorosis—the yellowing of the tissue between the veins. As chlorophyll depletes, chlorosis spreads and becomes necrosis which causes some leaves to die and drop. 

Late warning signs

When a cannabis iron deficiency progresses, the pale yellow color becomes brighter and covers entire leaves. More yellow foliage means your plant is struggling to thrive. 

Plant growth becomes slow, and any potential harvest is diminished or very poor. The leaves then turn bronze with small dark patches as the chlorosis spreads to the lower levels. Buds (if any) are stunted, smaller, less potent, lacking aromatics, and fewer than usual. 

Once it spreads to the lower areas, it’s a severe nutrient deficiency, and you need to act fast to save what’s left. Don’t panic. The good news is a cannabis iron deficiency develops slowly, so you have adequate time to spot the problems and fix it. 

How to fix iron deficiency in cannabis plants

Unlike other marijuana growing pains, iron deficiencies can be simple to fix if you act quickly. Since you now know what causes iron deficiency cannabis complications and how to spot these issues, let’s talk about fixing them. 

Nourish the soil 

Using additive products can add vital nutrients to the soil and prevent an iron deficiency in cannabis. They can also help maintain the pH level. Remember to flush the soil before starting any treatment so that your plants can easily absorb nutrients like iron. 

A cheaper and more environmentally friendly option for nourishing the soil is composting. This method decreases pH values by 0.1–0.2, which stabilizes the soil and improves drainage. Composting is successful in preventing iron deficiency cannabis problems because it helps the soil absorb vitamins easier. 

Cleanse and replenish

If your plants are suffering from a marijuana iron deficiency, a do-over may be in order. Flushing out the grow medium completely and replenishing it with nutrients helps plants recover and grow stronger. Here are steps to cleanse and replenish: 

  1. Flush out the grow medium using water with a pH level of 6.
  2. Follow up the next watering with a comprehensive nutrient solution like our standard pack fertilizer to nourish marijuana plants thoroughly. 
  3. Ensure you regularly check the pH levels to maintain the health of your flora.
Standard HMG nutrient pack
Standard HMG nutrient pack

Use iron chelate 

Spraying iron chelate on the yellow leaves is a temporary solution to a cannabis iron deficiency. This supplemental blend helps leaves regain chlorophyll, turning them green again. It only helps foliage that’s present, so with each new growth, you’ll need to spray again. 


Since iron deficiency cannabis complications first show with the upper leaves, pruning the yellow leaves off during vegetative growth could help. This technique is just a temporary option that may buy you some time to solve the deficiency before it spreads. 

Try not to over-prune. Trim off just enough to control the height and encourage top growth. While doing this, check pH levels and restore nutrient balance. It’s best to get to the root of the cannabis iron deficiency.

Elemental sulfur

Elemental sulfur is a long-lasting cure for iron deficiency in cannabis. It takes months to see the results, but you can say goodbye to your nutrient absorption problems for years to come. By lowering the pH, elemental sulfur makes nutrients like iron more available to flora. 

For best results, use the sulfur as a preventative by working it 6 inches into the soil a year before planting. When paired with composting, this mixture prevents any iron deficiency cannabis problems and increases the absorption of nutrients.

The key to fixing a cannabis iron deficiency is diagnosing and treating it early on. Here’s a quick guide for spotting signs of a cannabis iron deficiency and how to treat them: 

Problem/ sign Treatment 
Chlorosis in upper leaves Prune yellow leaves or use iron chelate.
Poor soil drainage Use a potting mix and avoid clay-based materials.
Imbalanced pH levelsMaintain pH between 6.5–6.7 and try using elemental sulfur to prevent pH imbalance.
Excess of other mineralsFlush the grow medium out and replenish with the correct amount of nutrients.
Overwatered Make holes in containers or flush the soil and replant. Water slowly or follow a watering schedule. 
Coco coir problems Ensure proper drainage—use nutrients and keep pH between 5.5.–6.5.
Stressed plants Take care of the plants— feed, water, and ensure proper drainage. It’ll fix itself in a few days.
Necrosis and lower leaf damage The damage is traveling— act fast. Flush out the grow medium with pH 6 water, re-nourish the soil, and maintain pH levels to prevent further damage.

Don’t panic: a cannabis iron deficiency is treatable

If you suspect a cannabis iron deficiency, check for yellow upper leaves and other warning signs. Act fast using the appropriate solutions, such as flushing the medium or balancing the pH. Your plants should go back to green in a few weeks. Ensure that you maintain their health by checking the quality of the grow medium regularly.
Remember that healthy plants start with top-notch cannabis seeds. Shop our selection of the finest quality marijuana seeds and nutrients to help your flora flourish. Happy growing!