By Steven Voser

Browse Deficiencies
Browse Deficiencies
Browse Deficiencies

Zinc is a mineral and one of many essential micronutrients necessary for a healthy plant diet. Despite cannabis requiring an astonishingly small quantity of it, it is nonetheless crucial for numerous physiological activities. Zinc is used by the cannabis plant to build proteins and macromolecular structures like membranes. It also fundamental to regulate enzyme function. Zinc is also co-factor of gene expression by stabilising both DNA and RNA structures. The growth hormone auxin requires zinc to operate.

Zinc deficiency cannabis plant

So if you have ever had a cannabis clone that for some unknown reason was not up to par with her sisters, it could have been a zinc imbalance. Most of the time you will notice a deficiency rather than excess. While excess zinc certainly does harm the plant, it is a much rarer occurrence, and the plant can deal with this situation better.

Excess zinc will primarily lockout iron which is easier to spot. On much rarer occasions, zinc levels may become so high it becomes toxic. If this occurs, the cannabis plant will quickly die off. This last scenario is almost implausible to think of!

So we will focus on zinc deficiency. A direct zinc deficiency is not a common occurrence and usually a side effect from tertiary causes. More often than not, it is pretty straightforward to fix.


Zinc is an immobile element. This means that once deposited it can no longer be relocated to other parts where it is needed the most. When a deficiency happens, older parts of the plant cannot distribute zinc reserves from one place to another, as it can with nitrogen or phosphorous. Therefore, early signs of zinc deficiency occur at the newest growth zones, generally at the top.

You may start noticing a plant is not growing as vigorously as it should. Internodal distance is progressively shortening. New growth shoots look a little different than earlier ones, like if they were shy to open up. Shoot tips will congregate, wrinkling up close together. Once they finally do open and start to stretch out, leaves will begin to yellow from the veins out.

From here on, if the issue is not quickly addressed the results could be very damaging. The yellowing will lead to some rust-like spotting. The tips and outer margins of the leaves will start shrivelling. Clear signs of irreversible chlorosis will be present.

By this point, the leaf is completely yellow, reddish and brown - becoming crumbly and crisp. Buds will contort, start drying up and will eventually die off. This is a doomsday scenario when no corrective measures are taken. With a little knowledge and care, it is something relatively simple to deal with.


Zinc deficiency cannabis leaves

Unless you are growing in an entirely new or unknown type of soil, the most common cause of zinc deficiency in marijuana is water pH imbalance. As pH becomes too alkaline, the roots become incapable of absorbing this mineral trace element. Other micronutrients like manganese and copper quickly become unavailable. Nitrogen and calcium start getting affected too.

If growing organically, your pH range is much more permissible than when using chemical fertilisers. Nevertheless it very important to control - something organic growers tend to disregard.

The main disadvantage of organic growing is that correcting deficiencies can take a lot more time. So the best solution is prevention. Keep monitoring your pH! Since organic growing is so permissive regarding pH, growers tend to stop checking their primary water source. In some regions, be it municipal or well water, pH can fluctuate up to 3 to 4 points within the same year.

A sudden influx of phosphorus can also cause a zinc lockout in weed. Are you a hydroponic expert grower that cannot explain why you are getting this deficiency all of a sudden? pH meters routinely calibrated, everything seems dialled in as always? It could be as simple as you having run out of nitric acid and switched over to phosphoric acid as pH-down. In excessively hard water regions, a high limestone and chalk content is calcium and magnesium rich, making for a strong pH buffer. Your once nitric acid stable system now uses significant amounts of phosphoric acid to deal with that strong alkaline water. This type of Phosphorous is readily available for intake by the plant, potentially pushing it into a zinc deficiency.


As a very last resort, adding any of these zinc sources can help out: zinc sulphate, chelated zinc or zinc oxides. There are numerous sources for these, depending if you want to stay completely organic or use chemical fertilisers. Keep in mind the golden rule of cannabis growing; less is more.

Tap water contains around 50% of all cannabis zinc requirements. If you know your soil is of good quality, then that rules out the most critical potential issues.

If you have just started using reverse osmosis water, beware you should be adding back what you remove. Start by adding a Cal-Mag mix to buffer your water. Check the numerous options commercially available, and you will find it is not difficult to find a good Cal-Mag product that also contains trace elements.

Once that potential cause for zinc depletion has been ruled out, you should perform a good flush. A good flush cleans out the roots of any salt build-up and removes stale water-pockets. Reset the feed, only a little lighter. Check your pH meter is calibrated and functioning well.

Because zinc is immobile, do not expect the marijuana plant to start looking better any time soon, even in hydro. In fact, once a zinc deficiency sets in and becomes visible, those affected leaves or buds will not look much better ever again. You will have to wait for new shoots to open and flourish to evaluate. This is easier during the vegetative phase when growth is explosive rather than mid to late bloom.

The trick is to learn how to spot these things as early on as possible. Keep a habit of constant monitoring the leaves from top to bottom. Anything seems out of the ordinary? The very first sign of trouble is almost always discolouration of the lush green tone.

The best growers will maintain strict diaries and perform continuous and rigorous analises. From registering day and night temperatures, relative humidity, checking light timers, checking drip systems for clogs or efficiency of pumps, all the way to water pH – it is imperative to keep things in check regularly. Everything is of crucial importance and it all adds up in the end.

So when you encounter a growing problem, remember - it all boils down to finding the cause and not just dealing with the symptoms.

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