Symptoms of Manganese Deficiency in Cannabis Plants

Manganese is one of the essential nutrients needed for proper cannabis growth, involved in photosynthesis, pollen production, nutrient metabolism, and more. Additionally, this crucial nutrient is necessary to ensure healthy root development to enable optimal growth for larger harvest potential. Therefore, when your strains, like  Agent Orange Auto-flowering cannabis plants, are suffering from a deficiency, it can result in chlorosis and the plants’ death.

Cannabis manganese deficiency can be mistaken for other weed plant deficiencies, so you need to know for sure that this is the issue. Once you notice there’s a problem, there are remedies readily available. Getting your farm soil analyzed should come before any treatment, as the analysis results will dictate your treatment choice.

So, how much manganese should your marijuana seedlings get, and how do you manage manganese deficiency? Today’s blog is a step-by-step guide to all you need to know about manganese and its role in your cannabis seed growth. We will also walk you through the symptoms of manganese deficiency in plants and how to fix manganese deficiency in weed plants. Let’s dive right in!

Close-up photograph of a cannabis bud nearing harvest time.
Everything growers need to know about critical nutrients for healthy growth.
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Why is manganese essential?

Manganese is a micronutrient needed for all plants to grow effectively. Generally, the nutrients plants need are classified either as macro or micronutrients, and you must have heard of how essential elements like nitrogen, phosphorus, and potassium are in maintaining plant growth. They are termed macronutrients because plants need them in large amounts for growth.

On the other hand, micronutrients are only needed in small quantities, typically milligrams, and that’s where manganese falls. The nutrient plays a significant role in the following ways:

  1. Photosynthesis

Manganese has a significant role in photosynthesis, where it acts as a cofactor for many enzymes involved in the process. It is also needed for the formation of chlorophyll, the substance that enables plants to trap sunlight and carry out photosynthesis.

  1. Nutrient metabolism

While manganese is only needed in trace amounts, it plays a key role in the metabolism of certain macronutrients like nitrogen and sulfur. Its involvement in enzymatic processes helps in utilizing these essential nutrients, aiding their uptake, utilization, and storage within the plant.

  1. Energy production

The sugars formed during photosynthesis are converted into energy components via the TCA (or Kreb’s) cycle. Manganese is also involved as a cofactor for enzymes in this reaction, making energy available for plant growth and metabolism.

  1. Root tip development

It promotes cell division at the root tips, enhancing root growth and overall plant nutrient uptake.

Understanding Manganese Deficiency

Cannabis growers must understand how critical a manganese deficiency can be since the lack of this key nutrient can lead to plant death. However, many growers often confuse this deficiency with others like a potassium deficiency.

Manganese deficiency in cannabis plants could be mistaken for any of the following cannabis nutrient deficiencies due to overlapping symptoms:

  • Calcium deficiency, which could appear as brown spots on the leaf surface like advanced manganese deficiency.
  • Magnesium deficiency also exhibits chlorotic leaves.
  • Fluctuating soil pH can cause brown spots on the leaves.

Since other weed plant deficiencies can show similar signs as manganese deficiency, you have to carefully observe your plants to evaluate the kind of nutrient deficiency they are showing. Specifically, with manganese, you’ll notice brown spots, which you won’t in something like an iron deficiency. When there’s a lack of manganese, the edges of the leaves stay green, but with other deficiencies, the leaves may turn yellow. Also, growers will notice that the veins don’t remain green when there’s not enough manganese.

Causes of Manganese Deficiency

The various causes of manganese deficiency in weed plants are tied to soil factors, and it is quite possible to be a doting farmer and still see your plants suffer from insufficient manganese. The risk factors range from low levels of manganese in the soil to elevated levels of other minerals, which prevent the plants from taking them up.

Here are a few factors to consider if you see manganese deficiency in your weed plants:

  • Elevated levels of magnesium and iron could prevent weed plants from taking up manganese in the soil.
  • Alkaline soils hinder manganese absorption. pH values between 5.5 and 6.0 are optimal for manganese absorption and healthy growth.
  • Calcareous soil–soil that is rich in limestone–or excessive use of lime fertilizer could cause weed plant deficiencies.
  • Swamps with alkaline pH and poorly drained soils could also lead to MN-deficient plants. If the soil drains too quickly, the manganese nutrients leach, while waterlogged soil limits oxygen penetration, creating an anaerobic environment that suffocates the roots.

Root pathogens and pests could also damage the roots of your plants, causing various weed deficiencies to occur at once.

Diagnosing Manganese Deficiency in Plants

There are several visual signs to look out for in MN-deficient plants. Like most plant diseases, some of the signs are general while others are more specific to deficiencies in manganese.

At the leaf level, the deficiency symptoms could manifest in a variety of ways.

Symptoms of cannabis leaf deficiency

  • Chlorosis

Chlorosis is one of the first visual cues of manganese deficiency and simply refers to the loss of pigmentation in plants. Chlorotic leaves start to lose their characteristic dark green color and become pale. The paleness starts at the base of the leaves before gradually spreading towards the apex.

Manganese deficiency in cannabis exhibits interveinal chlorosis, which is a common symptom where the loss of pigmentation occurs in areas between the leaf veins. This results in newer leavers suffering from yellowing in the areas between the veins. 

  • Wrinkled leaf tips and edges

When manganese deficiency progresses, the tips and edges of the affected leaves start to wrinkle, first becoming wavy–instead of sharp-edged–then curling and crinkling. As the leaf edges curl up, the ability to photosynthesize reduces and the leaf eventually dies.

  • Necrosis

Necrosis is a typical sign of advanced manganese deficiency in cannabis plants, where brown necrotic spots begin to appear on the leaf surface. This indicates that the leaf is dying and can harbor pathogens that would cause stunted growth.

Plant Level Indicators

The signs of manganese deficiency at the root level might not be visible from above the soil, but you would see the effects manifest in the shoot, leaves, and, most importantly, flowers of the weed plant. Some of the deficiency symptoms include:

  • Short, weak stems and branches that look unimpressive when compared with healthy plants
  • Reduced internodal spacing
  • Scanty canopy of leaves due to their small sizes and insufficient mature leaves, especially young plants
  • Poor root growth leads to ineffective nutrient uptake by the plants, eventually affecting their growth
  • Decreased crop yield with lower-level bud quality
Leaf blade showing loss of pigmentation on the leaf margins.
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Treating Magnesium Deficiency in Weed Plants

Your preferred treatment schedule for MN-deficient plants should be based on the causes. Since most of the causes are soil-related, you can take samples of your farm soil for analysis to narrow down the risk factors.

Based on the previously mentioned causes, we have come up with the following solutions for manganese deficiency in your weed plants.

Use appropriate fertilizers

If the deficiency in your cannabis plants is due to an absence of manganese in the soil, you need to get fertilizers. These contain most of the nutrients that are key components for the growth of your weed plants.

But applying fertilizers to your cannabis plants goes beyond simply getting a starter pack. True, they contain the essentials, from macronutrients like nitrogen to micronutrients like manganese and iron, but the starter packs don’t last very long and you still have to be sure of the ratio of manganese to iron and other micronutrients in the soil before choosing your fertilizers.

Other micronutrients compete with manganese for plant absorption, so high amounts of magnesium, iron, and calcium could still cause manganese deficiencies in weed plants. Water-soluble peat fertilizers provide an adequate mix of nutrients that works well with cannabis plants.

Use manganese foliar sprays

To correct cannabis manganese deficiency, you can get foliar sprays that deliver manganese directly into the plant’s leaves via the stomata. Stomata are pores in the cannabis plant leaf that allow for the diffusion of gasses and excretion of metabolic products like water and other gases.

With foliar sprays, there is no need for root absorption and the deficiency gets resolved. Get a manganese foliar solution with a mister and apply it according to the instructions.

Balance the soil pH

As we stated earlier, MN-deficient plants could result from an alkaline pH in the soil. In such cases, the solution is to reduce the soil pH to about 5.5 or 6.0 to promote manganese uptake from the soil. You can get pH up or pH down products to regulate your farm soil pH.

While treating manganese deficiency in cannabis plants, you should prune the dead leaves so that they don’t harbor pathogens. Leaves that are already affected by the deficiency cannot recover and they are best removed through pruning. Pruning should be done in stages, not all at once, to avoid stressing the plants.

You should take soil samples from your farm for analysis before you start the treatment of any weed plant deficiencies. This will inform you of existing parameters like the levels of other micronutrients, which could affect your choice of fertilizer or pH regulatory product.

How to prevent manganese deficiency in cannabis plants

Treating manganese deficiency in marijuana could be expensive, not to mention challenging. Prevention is best in such cases and here are a few tips to note to prevent cannabis manganese deficiency:

  • Check the soil pH regularly for any changes that might affect nutrient absorption, and keep in mind that pH levels between 5.5 and 6.0 are best for cannabis plants and manganese uptake.
  • Use balanced fertilizers if you ever have to use any. Make sure to dilute them before application on the soil.
  • Choose high-quality cannabis seeds to reduce the risk of issues like MN-deficient plants. These seed strains like Acapulco Gold Feminized seeds are resistant to common pests and diseases, yielding better flowers, and our seed collection at Growers Choice offers you a wide range of your preferred strains to choose from.

Since growing cannabis in the US–or at least in some states–became legal, we have seen different cannabis seed strains hit the shelves. Auto-flowering varieties like Deep Purple are getting more popular by the day, as they don’t require any light adjustments before they start to flower, although experienced farmers might still prefer the other photoperiod feminized strains such as Alien OG Feminized seeds. While flowering and harvesting can take longer, look out for a cannabis manganese deficiency during the growth phase!

Healthy cannabis seedlings two days after germinating.
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Cannabis manganese deficiency is a crucial issue to solve among weed farmers, even though it doesn’t occur commonly. As always, prevention is better than a cure, and you should understand your garden soil’s profile before you start planting. That way, you know which nutrients might be deficient and which nutrient boosters you may need.

If you already have cases of manganese deficiency in your weed plants, you can use any of the methods listed to tackle it. But won’t it be nice to get your weed farming started with the best seed strains available? After all, high-grade seed strains grow to be resistant to common pests and diseases, reducing the occurrence of issues like deficiencies.

Our collection at Growers Choice is a one-stop shopping experience for high-grade cannabis seeds. Need Afgoo Feminized or Do-Si-Dos Auto-Flowering Feminized seeds? Check out our online store and place your order today.


1. Will my plants recover from manganese deficiencies?

Yes, your plants can recover from manganese deficiency; only affected leaves cannot recover from the deficiency.

2. How can I fix manganese deficiency in my cannabis plants?

You can treat cannabis manganese deficiency by:

  • Using foliar sprays to deliver manganese directly to the leaves.
  • Supplementing the soil with the appropriate fertilizers to supply manganese via root absorption.
  • Balancing soil pH makes the manganese in the soil more available for uptake by the plants.

3. What are the symptoms of iron deficiency in weed plants?

Iron deficiency is very similar to manganese deficiency in that there is a loss of green pigment in the leaves (chlorosis). You can observe young leaves and flowers falling from the plant. The chlorosis hinders photosynthesis and affected leaves die along their leaves.

4. How can I distinguish between manganese deficiency and magnesium deficiency?

Both manganese and magnesium deficiencies are characterized by chlorosis of the leaves, but manganese deficiency exhibits interveinal chlorosis–that is around the veins–while the chlorosis in magnesium deficiency presents as spots in the center of the leaf.

5. How do I treat magnesium deficiency in my weed plants?

You can get magnesium salts, like sulfates or nitrates, to add to your farm soil to correct the signs of magnesium deficiency. Magnesium sulfate is the easiest remedy, but if your soil profile already contains enough sulfates, you can go for magnesium nitrate to treat magnesium deficiency in your weed plants.

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