Iron Deficiency In Cannabis Plants

Published :
Categories : Cannabis cultivation

Iron Deficiency In Cannabis Plants

Have you ever gotten, or currently have, yellow leaves in your cannabis plant? It could be an iron deficiency - a problem that is too often overlooked and can kill your crop.

Just like you and I, all living things need a very specific set of conditions to survive. But survival is not the only factor to take into account when growing cannabis. If you want good quality buds don’t expect to only water your plant every day and collect the yield when it’s done. This is so important that we’re writing an article on just one minuscule problem in the marijuana growing process: Iron Deficiency.


Nutrition is an extremely important step that should not be overlooked. Within the plant’s nutrients are the essential minerals that keep your plant healthy. Iron plays an important role during photosynthesis, contributing for both pigmentation and leaf respiration of your plant. It is also a key element in triggering the formation of chlorophyll, as enzymes require it to function properly. It’s particularly vital for younger, still growing tissues in marijuana.

Iron deficiency is a consequence of not enough supply of iron to the plant. Iron excess is also a problem, but we’ll be focusing on the one mentioned in the title. These two conditions are visually expressed in different ways. The major thing to look out for is the change in colour to yellow of your plant’s leaves. This will happen mostly with younger, inner leaves. Iron nutrient deficiency can appear very similar to a magnesium shortage. The key difference is that while iron deficiency will affect new leaves, the magnesium shortage affects older and lower ones. These leaves might even turn white. Most often you will see symptoms toward the top of the newer foliage. With this specific deficiency, affected parts of the plant have the ability to eventually return to their healthy colour. In most nutrient deficiencies, yellow leaves won’t really turn green every again.


An iron deficiency is usually caused by problems with pH, though sometimes it can be triggered by a stressful environment. If it’s the latter, it may clear up on its own after the period of stress is over. Make sure you’re doing everything correctly and that you’re not giving your plant too much of anything.

Iron is always available in the soil as long as it’s well-cared-for. Most of the times, the problem is that the plant can’t access the essential nutrients due to lock-out conditions.

One way you might stimulate lock-out conditions is by over watering your plant and/or not draining it properly. This will keep the roots under a lot of stress and prevent them from collecting the iron you want. Younger roots absorb the iron much better than older ones. Having a clear and cared root system is necessary to get an effective uptake.

There are other reasons a plant may not be able to absorb iron efficiently. High levels of carbonates, low temperatures or excess of phosphorus may cause a nutrient lockout.

This deficiency spreads slowly through the plant. Iron’s mobility is slow and this will give you a chance for recovery - if you act quickly. Remember that plants with strong genetics have, consequently, stronger immunities against adverse conditions. Make sure to buy your seeds from a trusted source.


It's possible that an iron deficiency may just be the result of overwatering. If you're growing in soil, let the medium dry out, then flush it with slightly acidic water with a pH of 6.0–7.0. Iron tends to get locked out with more alkaline water (pH over 7.0). If you’re growing hydroponically, you should flush your system with water that is even more acidic, shooting for a pH of 5.5–6.5. This should be your first step when spotting those yellow leaves.


If you still witness the same condition happening, try out an iron, calcium and magnesium supplement. Cannabis loves calcium and magnesium as these work beautifully with iron. A supplement of this kind can also help prevent such a deficiency. Even if your plant is not showing symptoms, you can never be too careful. Just make sure you’re not stressing it with nutrients as it might work in the opposite way.

If everything goes well, after a week or so, you’ll start to see a difference. Old leaves might not fully recover. These might keep their yellowish or already white colour; they’ll eventually fall out as they’re probably dead. Watch for the newly born ones. If these appear to be growing healthy, you’ve solved the problem.

We hope this helped you solve a current problem or prevent a future one. Prevention is always better than treatment and keeping yourself informed is half the battle. Be sure to keep up with the latest news in cannabis growth and to follow current literature and research on your favourite plant. There is still a lot to discover about it and there will always be problems to overcome. At least now, you can cross iron deficiency from your worries list because. Good luck with your crop and most importantly, have a good harvest.