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What to do with Cannabis Iron Deficiency

Problem: A cannabis iron deficiency is usually seen first on bright yellow new leaves, and the symptoms of a cannabis iron deficiency can sometimes appear alongside other cannabis nutrient problems or deficiencies. An iron deficiency is usually caused by problems with pH, though sometimes a cannabis iron deficiency can be triggered by a stressful environment and may clear up on its own after the period of stress is over.

The main symptoms of a cannabis iron deficiency are:

  • The newest leaves are completely yellow when they first grow in

  • The bright yellow (almost white looking) color on new growth is the signature sign of an iron deficiency.

  • Sometimes the affected yellow leaves are so damaged they’re beyond recovery. Other times the yellow parts of the leaves may begin to turn green as the plant continues to grow, starting from the tips and moving in toward the base of each leaf

  • Eventually, an entire leaf can become green and relatively healthy-looking, even though it started out completely yellow from an iron deficiency. The ability of yellow leaves to eventually turn green is another sign of an iron deficiency because for most other nutrient deficiencies any yellow leaves can’t truly turn green again.

A cannabis iron nutrient deficiency can look similar to a magnesium deficiency, but an iron deficiency will affect newer/upper/inner leaves, whereas a magnesium deficiency affects older/lower leaves.

Solution For Cannabis Iron Deficiency Note: Sometimes a cannabis iron deficiency (like all nutrient deficiencies) can be triggered by stressful conditions, and the plant may recover on its own after the period of stress is over.

1.) Adjust pH to Correct Range Easily the most common reason growers will see an iron deficiency is if the pH at the roots is too high. Iron tends to get locked at higher pH levels, especially when the pH is above 7.0, and iron deficiencies are more commonly seen in soil or coco coir than in hydro.

If you suspect your growing cannabis plant has an 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 – 6.5 pH range (although it’s generally recommended for soil growers to keep pH in the 6.0-7.0 range, iron tends to get locked out when the pH is higher, especially above 7.0)

  • In coco coir or hydro, iron is best absorbed by the roots in the 5.5 – 6.5 pH range

2.) Give the Right Nutrients The truth is, most cannabis growers don’t need to add more iron in response to an iron deficiency!

In fact, most growers have actually already given plenty of iron to their cannabis plants since it is found abundantly in most tap water. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to worry about adding more iron.

Iron deficiency symptoms caused by a true lack of iron are more likely to appear when a grower is using heavily filtered or reverse osmosis (RO) water to feed plants since any iron has been removed. There are other nutrient problems that can trigger the symptoms of an iron deficiency, for example, problems with calcium and magnesium, or an excess of copper can all lead to symptoms of a cannabis iron deficiency.

If you suspect you have an iron deficiency even though the pH is correct, or if you believe your system is truly lacking in iron, you may want to consider flushing your system with clean, pH’d water and add a supplement that contains Iron, Calcium, and Magnesium.

Cannabis loves Calcium and Magnesium, and they work for hand and hand with Iron. A Calcium-Magnesium supplement (often called “Cal-Mag” even though it also includes iron) can help prevent all of these deficiencies from appearing.

Cal-Mag products are suitable for Hydro, Coco Coir, and Soil (not organic, though). This may be a great choice because it also contains extra calcium and magnesium, which are deficiencies that are relatively common for cannabis, and often happen alongside an iron deficiency.

CaliMagic by General Hydroponics is the calcium, magnesium, and iron plant nutrient supplement that we use, though pretty much all other Cal-Mag products will work just as well for growing cannabis. 3.) Take Good Care of the Roots Iron deficiencies can show up with the plant having root problems or if the plant is overwatered, even if the pH is right and the iron is there. Proper watering practices help plants grow healthy and avoid a host of problems! 4.) Watch for Recovery After going through all the above steps, watch to make sure that the iron deficiency starts to clear up within a week or so (try to be patient since iron moves relatively slowly through the plant). The yellow leaves from before may not recover completely, especially if there was a lot of damage, but when new growth is coming in green, you know you’re good to go! Sometimes called “yellow leaf spot” or “leaf septoria,” this condition is caused by a fungus (or sometimes a bacteria) that attacks cannabis plants and usually appears in warm, wet weather. The symptoms first appear on the bottom leaves of the plant.

The spots may have darkened borders and may have a hard growth in the middle like a little pimple, but the thing that makes the spots the most unique is they are often very uniform, like little circles. Each spot is the receptacle of a spore which looks like tiny dark specks in the center of each spot.

Although the spots often appear yellow like in the picture below, they will start turning brown over time. So if you see round brown spots on your cannabis leaves it could also be caused by leaf septoria. The solution to Leaf Septoria

These fungus spores may stay in the soil over the winter, and attack your plants in the summer. Spores are also easily spread by wind and rain.

  • Immediately (and carefully) remove all affected leaves to get rid of as many spores as possible.

  • Prune any leafy parts of the plant to improve circulation through the plant

  • Avoid getting water on the leaves or laying on top of each other – you want to avoid moisture

  • Make sure to keep the ground under your plant clean. Rake away all leaves and vegetation. Adding mulch can also help prevent spores from spreading.

  • Keep plants healthy, sicks plants are much more susceptible to leaf septoria than healthy plants

  • One way to help prevent this fungus from attacking your plants is to rotate crop sites or move to a new location every year.

  • A copper based fungicide or Biofungicide may be effective at stopping the fungus from spreading though they are best used as a preventative.

  • Depending on exactly what’s causing your leaf spot, Neem Oil may be used to help combat the problem. Neem Oil will leave an unpleasant taste/smell on buds when used to treat flowering plants, so don’t let this stuff get near your buds! You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly, since neem oil and water can separate easily. Try spraying just a small part of the plant and see how it reacts first before spraying the whole thing.

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