Many people have no idea what the molybdenum nutrient (Mo) is. While it’s not commonly known, it plays a vital role in many aspects of life. Plants, animals, and even humans are dependent on it to stay healthy.

A lack of Mo stops organisms from functioning properly and is called molybdenum deficiency. Plants with a shortage thereof display damaged foliage and may die if left untreated. To help you keep your cannabis healthy and strong, we’re exploring everything you need to know about molybdenum deficiency in plants.


What is molybdenum?

If you’re a newbie grower, there’s a very likely chance you’ve never heard of molybdenum deficiency in cannabis. Many experienced cultivators know what it is, but few have had much trouble with it. Most times, the victims are inexperienced gardeners with a little too much enthusiasm.

So what exactly is the molybdenum nutrient? It’s an important trace mineral that’s essential for all life on earth. Humans and animals get it from grains, milk, or leafy greens. In turn, plants receive it directly from the soil. Its natural abundance is one of the main reasons a molybdenum deficiency is so uncommon.

Successful intake of molybdenum in plants is dependant on it appearing as molybdate in the ground. Research shows it appears less in sandy or acidic soils. Keeping a balanced pH is one way to prevent molybdenum deficiency in cannabis plants.

Depending on whether it’s a plant, animal, or person, molybdenum has varying uses. In humans and animals, it helps break down various compounds and proteins. Plants need it to convert nitrogen and other elements


What does molybdenum do for plants?

If you’re curious like us, you’re probably asking yourself, “what does molybdenum do?” While it might seem unimportant, you’d be surprised at the significance it plays.

The molybdenum nutrient plays a vital role in converting nitrogen into nitrates and nitrites. It then converts these to ammonia before synthesizing them into amino acids. These amino acids carry different functions from cell repair, growth, and nutrient distribution.

Many plants use nitrogen-fixing bacteria by giving them molybdenum to enter a symbiotic relationship. These bacteria ingest the mineral and use it to fix nitrogen in the air around the plant. Other vegetation types use it to make inorganic phosphorus into organic substitutes.

Molybdenum ensures healthy nitrogen, oxygen, and sulfur cycles, allowing plants to regulate water and nutrient flow. Each plant is different, as not all need the same amount of molybdenum. Unless your soil is particularly acidic, it’s rare to see molybdenum deficiency symptoms.


Molybdenum Deficiency in Cannabis


How to recognize molybdenum deficiency in cannabis

You can generally identify what’s wrong with your weed by looking at the leaves and branches. With molybdenum deficiency, however, it can be a bit harder to pinpoint. Cultivators often misdiagnose it as other ailments, which can be detrimental to your weed plants’ health.

When it comes to molybdenum deficiency, cannabis is affected in various ways. Symptoms vary depending on the medium used, and so does treatment. As with many other deficiencies, early detection is essential to the survival of your plants.


In soil

It’s often quite difficult to notice molybdenum deficiency in plants when you use soil. As a naturally occurring mineral, it’s very rare for plants to suffer from a lack of molybdenum. More often than not, a moly plant is the consequence of an imbalanced pH level.

Unlike a nitrogen deficiency which generally starts in the roots, molybdenum deficiency predominantly shows in the foliage. It can take some time for symptoms to appear, which is why it’s a bit tricky to notice. If you ignore them, they spread, and your cannabis plant slowly dies.

At first, you’ll notice it affecting a couple of leaves. Discolored brown leaves with crispy edges and orange-pink shaded centers are a tell-tale sign that you’re dealing with a molybdenum deficiency in cannabis. If you don’t remedy the situation, new leaves start curly and wither quickly.

The best way to determine whether it’s molybdenum deficiency is by testing the soil pH. Get a sample of about 2–3 spoons, and put it in a clean glass. Add distilled water to the same level and stir the mixture.

After 30 minutes or so, drain the mixture through a coffee filter to remove all the solids. Use litmus fluid or strips to test the water, and match the colors as indicated. If the results are lower than six or higher than eight pH, your plants are most likely suffering from molybdenum deficiency.



Molybdenum deficiency in cannabis grown in hydroponic systems is easier to detect and resolve. The direct interaction between roots, water, and nutrients means your marijuana plants show symptoms in hours instead of days. It also means when you fix the problem, your crops heal faster.

Like in soil, hydroponic plants’ leaves curl up and dry out when the marijuana plant has a molybdenum deficiency. The key difference is the time it takes to appear. The low pH threshold of hydroponic cannabis means you notice it faster.

Most cultivators use litmus paper because it’s affordable and easy to find. Electronic pH meters are a bit more pricey, but they’re more straightforward. Alternatively, you can use a pH solution. While not as popular as the others, it gets the job done.

If it’s your current water supply, you need to test the acidity. Collect a sample and test it with your preferred method. If the pH is wrong, you can fix it with the corresponding pH correction fluid.

Alternatively, mix your water and nutrient solution, then test it before feeding your plants. Ideally, your hydro setup should have a pH range of 5.5–6.5. Outside these ranges, they can’t absorb nutrients and therefore suffer from molybdenum deficiency.


Coco coir

Coco coir and palm peat are very interesting and sometimes tricky mediums to use in cannabis cultivation. Unlike soil, they’re very acid neutral, and unlike hydroponic setups, they don’t require a constant water flow. Molybdenum deficiency in cannabis grown in coco coir is rare because its food has enough of it.

The most common reason that cannabis in coco coir suffers from molybdenum deficiency is quite avoidable. Like soil and hydro systems, it happens when there’s a pH imbalance. Fortunately, you can identify it quickly, and therefore stop it from progressing.

Its inherent inability to retain nutrients and water makes molybdenum deficiency in plants grown in coco coir fairly easy to remedy. Unlike hydro and soil setups, you can’t exactly test the medium to check the pH. Instead, next time you feed them, keep the solution perfectly balanced, as all things should be.

When you mix your water and nutrients, test the pH level before feeding your cannabis plants. As with hydroponics, a pH between 5.5 and 6.5 is ideal for molybdenum uptake. After a few sessions, your plants will start recovering and growing healthy shoots.


What are the risks of molybdenum deficiency?

You might be uncertain as to what the damage can be or if it’s even worth taking into consideration. Trust us when we say it is. Not only will your plants create deformed leaves and flowers, but they’ll also eventually wither and die.

Molybdenum deficiency in cannabis turns leaves a pale white, which inhibits photosynthesis. Eventually, they crisp up, and the plant discards them. New growth suffers from a condition known as “whiptail,” leaving them deformed and inefficient.

While it might seem like the damage is purely aesthetic, Molybdenum deficiency is more sinister than merely affecting your weed plants’ looks. If you don’t treat your plants, they’ll stop producing flowers. Any expected yields can be written off, and whatever you recover is near unusable.

Left untreated, the vascular systems of your marijuana plant will stop functioning. Its health will start decaying, and segments begin dying. Eventually, necrosis sets in, and your ganja can become irreversibly damaged.


Treating molybdenum deficiency

Once you’ve established that your plants have a molybdenum deficiency, you’ll need to stop it from progressing as soon as possible. The longer you wait, the more damage your plants suffer. Please do yourself a favor, don’t wait until it’s too late.


Trim your weed

Firstly, cut off and trim all the dead parts of your cannabis plant. Do it as quickly as possible to avoid long-term damage. Don’t wait a few days to “see how it goes.” Plants with a molybdenum deficiency will see the necrosis spread if you wait too long.

Any leaves that are deformed, dried, or discolored should be taken off. Avoid leaving dead foliage behind, and pay close attention to their condition. If you leave any necrotic tissue, it can infect and kill the whole weed plant.


Molybdenum Deficiency in Cannabis


Flush the roots

If the coco coir or soil already started decaying, you need to flush the roots to stop the spread. Use lukewarm water to rinse the roots of any dead material. Make sure you wash all the necrotic tissue and excess salts out.

Roots of hydroponic weed plants affected by molybdenum deficiency are easier to clean. Drain your water supply, and flush the system. Rinse the roots, and make sure there aren’t rotting bits among them.


Fix the pH levels

Once you’ve rinsed the medium and the roots, you can replant them. Be careful that you don’t simply plant them into the same medium, only to have the issue arise again. If you’re using soil, test the pH before planting your weed. 

In hydroponic systems, mix your nutrient solution, and check the pH before introducing your plants. Similarly, make sure your mixture is balanced if you use coco coir. Nothing is as frustrating as going through all that effort, only to have to deal with a molybdenum deficiency again.


Similar nutrient deficiencies

Marijuana is a bit of a self-contradicting wildflower. Although it’s a very robust and resilient plant, it’s strangely fragile. The slightest imbalances in minerals and nutrients send alarm bells through the entire cultivar.

Inexperienced growers often find themselves perplexed by the different problems and how they present themselves. What confuses most people are the slight differences, as they’re so similar. Many other illnesses and nutrient shortcomings look like molybdenum deficiency symptoms.


Molybdenum Deficiency in Cannabis


Nitrogen deficiency

Nitrogen is a fundamental requirement for cannabis. A nitrogen deficiency in cannabis stops the weed plant from producing chlorophyll, which is the green pigment in leaves that allows plants to photosynthesize. 

While it looks similar to molybdenum deficiency, a lack of nitrogen turns the whole leaf yellow instead of only the outset edges. There’s no red on the leaves, and the blades don’t curl up the same way. It also doesn’t deform new leaves, and necrosis doesn’t occur as quickly.


Magnesium deficiency

Another condition that looks similar to a molybdenum deficiency is a magnesium deficiency in weed. The foliage also gets hurt and eventually dies. A significant difference is in how the damaged leaves look.

Unlike a moly plant, at first, it appears like nothing is wrong. Early symptoms include yellowed areas between the veins and a pale look. Blades appear to have burnt edges, and the tips are dead. If you ignore the symptoms, shoots become white, and the stems and petioles gain a purplish hue.


Calcium deficiency

Calcium deficiency in weed mostly appears in new growth. Darkened leaves and light brown necrotic spots are the first signs. Like with molybdenum deficiency in cannabis, leaf growth is stunted.

Calcium deficiencies are often part of a larger problem. Look for signs of magnesium or iron deficiencies to cover all your bases.


Iron deficiency

A cannabis iron deficiency in ganja is a nightmare. It’s easy to prevent but difficult to cure. Although symptoms may look like molybdenum deficiency in cannabis, the damage happens faster.

If your cultivar leaves go yellow while the veins stay dark green, you’ve got an iron deficiency. Symptoms start at the top of the marijuana plant, in the middle of the leaf, and gradually move downwards. As with a calcium and molybdenum deficiency, look for indications of other conditions that might be affecting your plant at the same time.


Preventing future incidents

You can buy the best cannabis seeds in the world and still fall victim to molybdenum deficiency. In truth, the seeds don’t influence the likelihood of deficiencies or diseases developing. The best thing you can do is to test your medium, nutrients, and water before every feed to stop it from happening again.

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