Manganese deficiency in cannabis plants

How to Spot and Correct a Manganese Deficiency in Cannabis Plants


When I first started growing cannabis, Manganese was the furthest thing from my mind. Heck, I probably thought that Manganese was a type of pasta dish…

In time I learned what Manganese was and I learned the hard way. In my very early grows, I regularly struggled to maintain good pH in my soil and it consistently resulted in different deficiencies. I only had a cannabis Manganese deficiency once and I was left scratching my head as I misdiagnosed it time and time again.

So to save you the pain, I will detail how to spot and correct a Manganese deficiency in cannabis plants and how to prevent it from happening in the first place.

Manganese deficiency in cannabis plants

(Mn) Manganese: A catalyst in the growth process and formation of oxygen in photosynthesis.

Deficiency: Manganese deficiency causes yellowing of leaves between the veins and failed blooms.

Toxicity: Excessive Manganese can reduce the availability of Iron that the roots can take in.

Micronutrient: Absorbed in small to minute quantities. They are generally less well known than the macronutrients since most plant foods don’t contain them.

What does Manganese do for Cannabis Plants?

Manganese is one of several micronutrients that are necessary for growing healthy cannabis plants that produce high and tasty yields. It plays a key role in photosynthesis where it helps in the formation of oxygen in photosynthesis.

Manganese is also involved in the activation of a few complex enzymes that enable plant growth and metabolism.

A deficiency in Manganese is quite uncommon but when it happens it can quickly send your plant spiraling into a state of malnutrition, often marked by the conspicuous symptom of yellow leaves, brown spots, and dead patches that are very difficult to diagnose.

Recognizing a Manganese Deficiency

Detecting a Manganese deficiency can be very tricky because the symptoms are subtle and easy to misdiagnose. The main visible symptom is yellowing leaves and brown spots later on as the condition progresses.

Yellowing and brown spots are common to most cannabis nutrient deficiencies so at first sight, you will likely suspect another nutrient to be the culprit.

Manganese deficiencies are not very common so don’t jump to any conclusions before properly diagnosing the symptoms using the list below.

Early Stages of Manganese Deficiency

In the early stages, a Manganese deficiency presents itself in the form of slight discoloration, usually manifesting as yellow leaves due to stunted photosynthesis and decreased chlorophyll production.

Unlike a Nitrogen deficiency, for example, where the entire leaf yellows uniformly, Manganese deficiency typically causes a mottled yellowing pattern of interveinal chlorosis (yellowing between the veins), affecting primarily young leaves towards the top of the plant.

The Progression of Manganese Deficiency

As the deficiency progresses, the symptoms become a bit more evident but still very difficult to confidently diagnose.

The yellowing of the leaves intensifies, with more prominent signs of interveinal chlorosis. The leaf veins themselves remain green which is unique and a good start-off point for making a diagnosis.

Late Stages of Manganese Deficiency

In the later stages, the yellow areas turn into brown necrotic spots (dead spots), and you will notice severely stunted growth. Finally, the leaves start to curl, wilt, and eventually fall off.

At that point, there is usually no saving the plant no matter which corrective actions you take. It’s especially sad if this happens during the flowering stage because you may lose your whole crop.

Manganese deficiency in cannabis plants

What Causes Manganese Deficiency and What are Common Misdiagnoses?

Manganese deficiency in cannabis can result from a variety of factors but the most common reason is improper pH balance hindering nutrient uptake, and producing nutrient lockout.

pH imbalances in the growing medium prevent the plants from absorbing one or more essential nutrients which can lead to lockouts. Marijuana plants prefer a pH of 6.0-7.0 in soil and 5.5-6.5 in hydroponic systems so keep a pH meter around in your grow.

How to Fix a Manganese Deficiency in Cannabis Plants

Now that you know the symptoms of a Manganese deficiency, you should be able to diagnose it with a little more ease than I did in my early years as a grower.

Hopefully, you have made the diagnosis before necrosis starts setting in because it will speed up the recovery time significantly. If you perform the steps below, your plants should start producing new healthy growth in 7-15 days.

A multifaceted approach usually works best in treating an Mn deficiency. We will look at soil amendments, adjustments in pH, and improving irrigation practices for prevention.

First, ensure the pH is within the appropriate range for cannabis growth (between 6.0 and 7.0 for soil-grown plants). This will promote optimal nutrient uptake and prevent further deficiencies. This is most likely the only correction you will need to perform but if the pH is too off or if you are unsure of your diagnosis, I recommend flushing the system and reapplying a balanced cannabis nutrient mix.

Next, avoid overwatering and ensure proper drainage for your plants. Waterlogged soil can promote Manganese deficiency by making it harder for roots to up nutrients.

Lastly, closely monitor your plants. It may take a few days or weeks before visible signs of recovery.


Learn how to spot and fix cannabis nutrient deficiencies

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