Cannabis Manganese Deficiency: Symptoms, Causes & How to Fix It

Manganese (Mn) is a micronutrient that plays a direct role in photosynthesis: it is required to split water molecules, the first step in turning light into energy. It also activates enzymes involved in growth and nitrogen use. Even a mild shortage reduces photosynthesis efficiency, which slows growth and limits yield. 
Cannabis manganese deficiency image

How to recognize manganese deficiency

Manganese has limited mobility, so symptoms usually appear on young and middle leaves. 

  • Yellowing between the veins with a mottled, patchy look.
  • Veins stay green, often with a band of green tissue alongside them.
  • Small brown or tan dead spots scattered across the yellow areas.
  • In severe cases, leaves turn brown and drop off, and growth slows.

Tip: iron deficiency yellows new leaves more evenly and appears at the very top of the plant. Manganese deficiency looks mottled, with brown spots, and often affects slightly older leaves too.

Common causes

Manganese becomes much less available as pH rises toward neutral and above. Aim for roughly 6.0–6.5 in soil and 5.5–6.2 in hydroponics and coco. 

How to fix manganese deficiency in cannabis

  1. Check and correct pH at input and runoff (or in the reservoir).
  2. Review your iron supplementation: lower it if it is excessive.
  3. Use a complete micronutrient mix or a chelated manganese supplement at label rates.
  4. Improve drainage and avoid overwatering.
  5. Watch new growth: damaged leaves won't recover, but new leaves should come in healthy within about a week.

Don't overcorrect: watch for toxicity

Manganese toxicity is common when pH runs too low, below roughly 5.5. Signs include brown spots on older leaves and induced iron deficiency in new growth. Keep pH stable rather than chasing symptoms with supplements. 

Deficiency at a glance

 

Manganese deficiency 

Mobility 

Limited — young and middle leaves first 

Key signs 

Mottled yellowing between green veins, scattered brown spots 

Main causes 

High pH, excess iron 

Ideal pH 

Soil 6.0–6.5, hydro/coco 5.5–6.2 

Common mix-up 

Iron deficiency, magnesium deficiency, low-pH toxicity 

 

How Dosatron helps

Manganese sits in a narrow window: too high a pH locks it out, too low a pH makes it toxic. Dosatron proportional pumps can inject both pH adjusters and micronutrient solutions into the irrigation line at a fixed ratio, keeping pH and micronutrient levels stable across the whole grow. Water-powered and non-electric, they hold their dosing rate regardless of flow or pressure changes. 
Need advice about stable pH and micronutrient dosing.

FAQ

Young and middle leaves, because manganese have limited mobility. 

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