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Manganese Deficiency: Fixing Your Sick Marijuana Plant

When a manganese deficiency occurs in plants, their leaves will start to turn yellow. The marijuana leaves will then turn brown and eventually die. If left untreated, the deficiency could destroy the entire plant. A manganese deficiency can be difficult to spot, as it looks similar to other marijuana deficiencies. 

Why do marijuana plants need manganese?

late signs of manganese deficiencyManganese plays an important role in photosynthesis. Manganese also helps the plant to absorb nitrogen, which is essential for the health of the plant. It also helps the pollen tubes grow, which helps with pollen production. It also strengthens the roots during their development.

Although a micro nutrient, it’s clear that manganese is important to the healthy growth of any plant. Growers must be able to identify the signs and symptoms of a manganese deficiency in order to correct it.

What are the signs of a manganese deficiency in a marijuana plant?

Cannabis leaf problems are the first signs that a plant is suffering from a manganese deficiency.

  • The areas on the leaves between the veins will begin to yellow on new leaves.
  • Brown spots may start to appear on leaves.
  • The leaves may also begin to curl under.manganese deficiency marijuana diagram

Without healthy leaves, a plant cannot thrive. When a deficiency is occurring, the overall growth of the plant may be stunted. Therefore, it may mot provide the abundant yields most growers hope for.

This damage will start at the top of the plant, seen in the newer, younger leaves. It then will work its way down to the older leaves at the bottom of the plant. It's important growers identify the problem as quickly as possible, to avoid killing the plant.

Manganese deficiency or iron deficiency?

It can be easy to mistake a manganese deficiency for an iron deficiency. However, if the plant is mistake and treated for an iron deficiency, it can make the manganese deficiency worse. This is because the excess of iron in the grow medium will essentially lock manganese out. So the plant won’t be able to absorb it anyway.

A sign of this deficiency that separates it from an iron deficiency is that the leaf will turn more yellow. But the margins around the veins will remain a dark green.

iron deficiency cannabisThere are many possible reasons a plant may experience a manganese deficiency. Too few nutrients may have been given, or perhaps no nutrients were provided at all. Plants grown in soil may have been overwatered, essentially locking out the space for the plant to absorb the nutrients.

The most common cause of a deficiency however, is that the cannabis ph level is off. Plants need to be in an environment that has a neutral ph level. If that level is too high and the grow medium is acidic, the plant will experience manganese lockout.

How to fix manganese deficiency in a marijuana plant.

There are several ways to fix a manganese deficiency. The first step for those growing in soil is to flush the roots, if possible. This will wash away any nutrient salts and ensure there is no buildup of other minerals. After flushing the roots with ph-balanced water, they should be dried out as much as possible. But not entirely.

All growers then need to flush their entire system with ph-balanced water. This will bring the growing medium back to neutral, so the grower can start from scratch. Then the ph level in the soil or coco coir can then be adjusted to the proper levels.

PH Levels for grow mediums

For soil, the right ph level is 6.0 to 6.5. Those growing in hydro or coco coir setups, should keep a ph level in the growing medium between 5.5 and 5.9.

Once these steps have been taken, growers should see improvement in the new leaves. The leaves that have already been affected likely will not recover. These leaves should be removed so all nutrients can be directed to the new, healthy shoots. If no improvements are seen, a manganese chelate can be given to the plants. There are many brands on the market that also offer alternatives for those growing organic cannabis.

Those growing in soil should also ensure there is plenty of drainage in their pots, or in the ground. When too much water is left sitting around the roots, it is impossible for the plant to absorb the nutrients.


Manganese is an important nutrient and is responsible for many parts of the plant’s growth. The good news is that it is relatively easy to treat. Growers that follow these steps can sit back and watch the new, healthy growth forming on their recovered cannabis plant.

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MSNL Team MSNL Team / 4th October 2018

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