Manganese Deficiency

Manganese deficiency is a shortage of a trace element the plant uses in photosynthesis itself, specifically in splitting water inside the leaf. It is uncommon and it is almost always a side effect of something else you did.

What you are seeing#

New and recently mature leaves in the upper half of the plant. Manganese is only slightly mobile, so the damage skews toward the top.

The tissue between the veins turns pale yellow while the veins hold a clear green. So far this is the same picture as iron. What separates manganese is what comes next: small dead flecks, tan to dark brown, appear scattered through the yellowed areas, usually starting near the base of the leaf and spreading outward.

Those flecks stay small and speckled rather than merging into large patches. The leaf keeps its normal size and shape, and node spacing is normal.

Lower leaves generally stay green. In a severe case leaves go pale overall and drop early.

Why it happens#

Manganese availability falls off above roughly pH 6.5. It is also directly antagonized by iron, so people who dose a chelated iron product to chase a yellow top frequently produce this instead.

Beginner causes:

• pH above 6.5 in soil or 6.2 in coco and hydro.
• Over-supplementing iron in response to a misdiagnosed yellow top.
• Overly wet, low oxygen root zones.
• Heavily limed or naturally alkaline soil.
• Reverse osmosis water with no trace element package in the feed.

How to fix it#

1. Test runoff pH before anything else. Target 5.8 to 6.3 in soil and 5.6 to 6.0 in coco and hydro. Manganese availability improves as pH drops within the safe range.
2. Stop any standalone iron supplement you have been adding. If you started dosing iron in the last two weeks and this appeared, that is your cause.
3. Flush with 2 pot volumes of pH 6.0 water if runoff reads above 6.8, then resume a normal complete feed at half strength.
4. Improve root zone oxygen. Water to runoff, then wait until the pot is light before the next watering.
5. Over the next week, rely on a complete base nutrient with a full micronutrient package rather than individual trace products. Manganese is needed in tiny amounts and the base feed almost certainly contains enough.

How to tell it apart#

Versus iron deficiency. These are the closest pair in the whole set and they often occur together. Iron deficiency yellows new growth cleanly and brightly, with sharp green veins and no marks. Manganese deficiency yellows more dully and stipples the yellowed tissue with small dead tan flecks fairly early. Speckles present means manganese. Clean bright yellow means iron.

Versus zinc deficiency. Zinc deforms the plant. Leaves come in narrow, twisted and bunched on short internodes. Manganese leaves shape and spacing alone and only affects color and speckling. If the top of the plant is compressed and deformed, it is zinc.

Versus magnesium deficiency. Position again. Magnesium is fully mobile and starts on the oldest bottom leaves, and its spots are larger, rustier and merge into patches. Manganese sits in the upper half of the plant and its marks stay as fine flecks. Bottom means magnesium, top means manganese.

Versus pH lockout. Effectively the same event in most grows. Manganese is rarely actually absent from a complete feed.

How long until it looks better#

The flecked tissue is dead and will not clear. Those leaves keep their speckles for good, and the yellowed areas mostly stay yellow.

After a pH correction, new growth should come in evenly green and unmarked within five to eight days. That is your only real signal. If new leaves are still flecking after ten days at verified correct pH, check whether you are still adding iron or any other single element product, because antagonism is the more likely cause than an actual shortage.