By RQS Editorial Team

Browse Deficiencies
Browse Deficiencies
Browse Deficiencies


Yellow leaves that rapidly degenerate and turn brown is the nasty calling card of manganese deficiency. Immobile and confined to new, fresh growth, this particular malady is relatively uncommon. However, when cannabis plants have manganese deficiency, it is almost always misdiagnosed as something else. Anything but manganese deficiency.

It usually costs a grower a couple weeks of trial and error before corrective action is applied to treat the manganese deficiency. By this time, growth has all but stopped completely. Much of the upper growth will be a discoloured, wilting patchwork of light fading green, yellow and brown.

Manganese deficiency


High pH in any medium and/or excessive iron is the number one root cause of manganese deficiency. Of course, we mean that literally. Moreover, pH above 6.0 across all substrates will render manganese unavailable to the roots. This is bad news. Manganese is essential to chlorophyll production and photosynthesis.

Even if the grower accurately diagnoses manganese deficiency early, increasing micronutrient supplementation without getting the pH into the 5.5-6.0 range is futile. It may worsen the situation and lead to an iron build-up that will lockout manganese.


Should you catch the manganese deficiency in its early onset, a flush with pure 6.0pH water is a great start. Followed up by a carefully adjusted 6.0pH light nutrient solution, your plants should get back on track. Watering and feeding will need to be closely monitored to prevent recurrence.

Manganese deficiency table graphic


On the other hand, if you have lost time troubleshooting and increased micronutrient doses in the process, we can help. Again, start by flushing plants as above. Stick to the program and apply a light nutrient follow-up feed. Odds are, iron could well be locking-out manganese at this point. Plus the damage (brown crispy leaves in particular) will not recover. If your marijuana is still in vegetative growth, top the plants - why not?

However, if manganese deficiency has hit the crop during bloom, you still must prune away the affected growth. Leaving necrotic growth is a huge risk. Don’t invite diseases and pathogens. Look at it as an opportunity to experiment with defoliation. Remember to prune in stages as stripping plants suddenly bare is highly stressful.


The best way to avoid manganese deficiency is to ensure every watering is pH-adjusted to the optimal level for your specific growing medium. Take note that 6.0pH is the upper threshold for manganese. Check to confirm. Invest in a pH pen.

Alternatively, high-quality cannabis-specific nutrients and cultivation substrates are the best insurance policy against common and obscure marijuana maladies. Nutrient lines that can self-correct to the perfect pH level for the substrate are very convenient and diminish the need for pH pens and meters.


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