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Iron Deficiency

by Nebula Haze & Sirius Fourside

Problem:  An iron deficiency in cannabis is relatively rare, and the symtpoms of a cannabis iron deficiency appear most often alongside other nutrient problems or deficiencies.

The main symptoms of an iron deficiency are:

  • Yellowing of upper fan leaves

  • Yellowing of smaller inner leaves

  • Veins of leaves stay green

Sometimes affected leaves will even appear white. Often the symptoms appear near the top of the plant on newer leaves.

Cannabis Iron deficiency - top leaves are bright yellow

With an iron deficiency, the veins of the leaves sometimes tend to stay green even while the rest of the leaf is completely yellow. Other times there's just yellow, with no signs of green.

This nutrient deficiency can look similar to a magnesium deficiency, but an iron deficiency will affect younger/upper/inner leaves (where a magnesium deficiency affects older/lower leaves).

This info-graphic has more information about iron and your marijuana plantThis young marijuana plant appears to have an iron deficiency

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 causes 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.

This cannabis iron deficiency is actually caused by too much nutrients (the grower added too much chicken manure as fertilizer)

Immediately after adding chicken manure and watering, the plant started producing bright yellow, almost white leaves that immediately dried up and died. 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

Iron tends to get locked at at higher pH levels, especially when the pH at the roots is above 7.0, and more commonly in soil than in hydro.

Iron can also react with other nutrients, causing other nutrient lock-outs at the same time. If you are supplementing with iron, make sure you read the label to minimize any problems or interactions with your current nutrient system.

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 - 7.0 pH range (iron tends to get locked out when the pH is above 7.0, and if you suspect an iron deficieny, you may wan to consider lowering your root pH to ~6.5 just to be safe)
  • In hydro, iron is best absorbed by the roots in the 5.5 - 6.5 pH range

Watch to make sure that the problem starts to clear up within a couple of days to a week, since iron moves relatively slowly through the plant.

After correcting the cause of an iron deficiency (usually too-high pH), you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy, without the yellowing of new leaves as you were seeing with the iron deficiency..

If you suspect you have a iron deficiency even though the pH is correct, flush 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.

Iron deficiencies often appear alongside deficiencies with calcium and magnesium, or an excess of copper. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case one these deficiencies appear.

If you think you need to supplement with extra iron, a product known as Cal-Mag is suited for Hydro, Coco Coir, or Soil (not organic, though). This is a great choice because it also contains extra calcium and magnesium, which are deficiencies that often happen alongside an iron deficiency.

Botanicare Cal-Mag Plus is a calcium, magnesium, and iron plant nutrient supplement. General application is to mix 1 tsp (5ml) of Cal-Mag into each gallon of water.

Guaranteed Analysis: Nitrogen (N) 2.0%, Calcium (Ca) 3.2%, Magnesium (Mg) 1.2%, Iron (Fe) 0.1%

Derived from: Calcium Nitrate, Magnesium Nitrate, Iron EDTA

Watch to make sure that the problem starts to clear up within a couple of days to a week, since iron moves relatively slowly through the plant. Old growth may not recover, but new growth should be healthy.


If you cannot get rid of a cannabis iron deficiency, please consult our 6-Step Cure to 99% of Cannabis Growing Problems

Cannabis Iron Deficiency -
Big Symptom Picture: 
Leaf Color: 
Pale Color Leaves
Yellow Leaves - New Growth
Yellowing Between Veins
Veins of Leaves Stay Green
Leaf Symptoms: 
Upper Leaves / Newer Growth Affected
Small Inner Leaves Affected
Leaf Tips Die
Yellowing Between Veins
Veins of Leaves Stay Green
Slow Growth
Twisted Growth
Abnormal Growth
Plant Symptoms: 
Slow Growth
Twisted Growth
Other Symptoms: 
Buds Not Fattening