How-to Tell if Your Medical Marijuana Plants Are Nutrient Deficient

I remember sitting there debating for hours, “… Should I?”

A monologue performed for an audience of dancing cannabis plants, moving to the restless beat of fans.

I posted the picture up on Instagram anyway: a magnesium-deficient fan leaf that should have been overshadowed by the voluptuous bud in the frame but instead was all I could focus on in the foreground. “I hope no one notices.”

There weren’t traces of negligence; the deficiency was no cry for help. I wasn’t expecting the Canna-services to barge in, break down tents, and remove our girls for improper cultivation abuse. No, the issue was this particular strain was Cal-Mag thirsty and despite attempted efforts she was never satiated.

From Boron, Calcium, and the constantly re-appearing Nitrogen, to Potassium, Sulfur, and even right down to Zinc–we’ve all had to scavenger hunt through the nutrient-deficiency-alphabet at some fear stricken moment or another, usually skipping straight to N.

To help navigate the alphabet, let’s take a look at some of the most prominent tell-tale signs that your medical marijuana plants are nutrient deficient. The best way to nip deficiency issues early on is to give these girls the attention they not only yearn for, but also deserve. Listen to your ladies, they’re constantly chattering away at you.

Note: Nutrients get locked out at certain pH levels. The best range for nutrients to be absorbed is between a pH of 5-7 and a (TDS) range of 800 to 3000 PPM. I’ve read so many sources that state 6.8 is ideal. Following every nutrient in the following list are the ideal pH ranges for optimum nutrient uptake in soil, hydro, and soilless media.

(B)oron (soil: 5-7; hydro-soilless: 5-6)

Boron is an immobile micronutrient involved in seed production, pollen germination, cell division and protein formation. Needless to say it’s pretty important.

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Younger leaves get targeted by yellowing first. As the deficiency progresses leaves look bronzed or scorched, have hollow stems with yellow-brown leaves, necrotic spots between veins, and thickening of leaves occurs. First signs can also include abnormal growth tips. Boron deficiency resembles Calcium deficiency in that plant growth is stunted, discoloration and yellowing of leaves occurs, and bud formation is disrupted.  Too much Boron and you will recreate fall with the amount of leaves falling off and eventually leading to the death of your plant. 

(Ca)lcium (soil: 6.5-7; hydro-soilless: 5-6)

Marijuana Calcium Deficiency
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Calcium is an immobile macronutrient that tends to concentrate in the roots and older growth since it moves slowly within the plant. Ca enhances the uptake of Potassium in the roots and also contributes to root growth and cell division.

If you begin to notice traces of yellow/brown spots with distinct brown outlined edges and new growth then you have a girl on your hands that is in need of some Calcium. Too much Calcium at a young age in this case does not build healthy bones, but instead stunts a young seedling’s growth. So remember moderation is the best rule of thumb.

(Cu) Copper (soil: 5-7; hydro-soilless: 5-6)

Copper helps in carbohydrate (sugar) metabolism and oxygen reduction.

Copper deficiency can be seen in plants that are struggling to mature during veg. Other red flags to keep an eye out for is stunted growth, new growth that is wilted and irregular, and leaves with either a bluish hue or with bleached veins. Too much Copper acts as poison and kills the plant completely.


Copper Deficiency Marijuana Plant
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(Fe) Iron (soil: 4-6.5; hydro-soilless: 5-6)

Iron is responsible for electron transportation during photosynthesis and is an immobile micronutrient.

Dark green veins with yellowing leaves or pale/white tissue between the veins begin to occur when a plant is deficient in Iron. Yes, it does sound similar to magnesium deficiency except where there is yellowing in magnesium deficiency, there is white in Iron deficiency. Too much Iron and it will starts to a resemble pH imbalance with brown spotting on fan leaves.

(K) Potassium (soil: 6-7; hydro-soilless: 5-6)

Potassium is a macro mobile element involved in water transportation and is necessary during all stages of your girls’ growth. Keep in mind that it has an important role in the development of flowers, which means that during bloom I may be guilty of “accidently” throwing in an extra splash of a fertilizer containing higher K values. When levels of potassium are ideal your plants will have higher resistance to diseases and have thicker stems. Sources also say healthy plants have less chances of getting infested by pests.

Signs of Potassium deficiency are leaves with the tips curled and the edges burned off, weak branches, stunted growth, and red color on older leaves with yellowing between the veins. Low relative humidity can lead to potassium deficiency, which also affects the growth of buds when in flower.

Potassium toxicity can lead to salt damage and acid fixation of the root system. Too much K can also cause a reduced uptake of Magnesium and Calcium in an attempt to restore molecular balance.

Marijuana Nutrient Deficiency and Abundance Chart
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(Mg) Magnesium (soil: 6.5-7; hydro-soilless: 5-6)

This mobile micronutrient breaks down enzymes, fosters healthy leaf production and, like Nitrogen, also produces chlorophyll.

Magnesium deficiency screams at you from a mile away, reaching out with its green veins drowning in yellow leaves. New growth exhibits lime green tips as the deficiency progresses. In extreme cases if the deficiency isn’t attended to brown/yellow leaves will begin to fall off your plant without withering.

Do not excessively add Mg to try and fix the deficiency. Doing this will only lock out other nutrients like Calcium and increase toxic salt build ups, resulting in either white or yellow colors on the outer parts of your plant.

(Mn) Manganese (soil: 5.5-6.5; hydro-soilless: 5-6)

This immobile micronutrient participates in the production of chlorophyll and photosynthesis by aiding in enzyme break down.

Yellow or brown spotting on young leaves indicates manganese deficiency. Older leaves may have gray spotting. Too much Mn could lead to Iron lock out and lead to an iron deficiency.

(Mo) Molybdenum (soil: 7; hydro-soilless: 5-6)

 Molybdenum helps plants access Nitrogen from the air.

Marijuana Plant Molybdenum Deficiency
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Pale, scorched, yellowing middle leaves and twisted younger leaves are indicative of a Molybdenum deficiency.  Older leaves are affected first. While it may resemble a Nitrogen deficiency the difference is in color; red tips that move inwards toward the middle illustrates a lack in Molybdenum levels.

Too much Molybdenum doesn’t harm the plant too much; instead it becomes more of a health hazard to humans if consumed, which is a good thing to keep in mind if you farm and harvest your own medicine.

(N)itrogen (soil: 6-7; hydro-soilless: 5-7)

This macro mobile element is responsible for the production of chlorophyll, amino acids, proteins and most growers’ headaches.

Visual symptoms of Nitrogen deficiency include poor growth rate and pale green or yellowing leaves (chlorotic leaves) due to insufficient production of chlorophyll. Chlorotic leaves will begin to appear in older (lower) leaves first as the plant attempts to compensate for low Nitrogen levels by moving N from older tissue to newer, more important tissue.

Magnesium and Nitrogen deficiencies most often get confused with one another. The best way to differentiate between the two is to pay attention to the discoloration of your leaves. If yellowing starts off at the tips and works its way into the leaf, N will be your culprit. Magnesium deficient leaves yellow in their entirety, leaving only the veins to remain green.

When levels of Nitrogen get offset the girls suffer greatly. We’ve seen what happens when we have too little N, but what about when there is too much? If your plant has an overall darker green appearance, delayed maturity, and in extreme cases leaves that resemble a downward facing claw, then your plant has had too much N to eat, and then some! Good thing these girls bounce back quickly. A good rinse should fix the problem: if your plants sit in a 5gal container then a 10gal rinse would suffice—double the H2O as compared to container size.

(P)hosphorus (soil: 6-7; hydro-soilless: 5-6)

Phosphorus is a macro mobile element that is responsible for root growth and is essential during reproductive stages (absolutely crucial during bloom).

Low levels of Phosphorus results in dwarfed and stunted plants. Cold weather (below 50°F/10°C) makes absorbing Phosphorus extremely difficult for the plant. Visual representations of P deficiencies are an overall dark green color with hints of purple, red, or blue on the fan leaves, and a dwarfed size.

Too much P suppresses the uptake of Iron, Potassium, and Zinc.

Symptom Elemental Chart
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(S)ulfur (soil: 6-7; hydro-soilless: 5-6)

Sulfur is an immobile micronutrient that aids with vegetative growth, contributes to root growth, and supplies chlorophyll and plant proteins.

Stiff, brittle leaves and hard, thin stems are indicative of Sulfur deficiency. Sulfur deficiency also results in yellowing that starts from the back of the leaf and works its way toward the middle. Some plants may show red/orange hues instead of yellow.

(Zn) Zinc (soil: 5-7; hydro-soilless: 5-6)

Zinc is a versatile immobile micro nutrient. It is involved in the production of leaves, stems, and branches. Zinc also plays a role in plant size and maturity since it is a component of enzymes such as auxin, a plant growth hormone.

Appearing on older leaves first, Zinc deficiency can be seen in bleached spots between veins. More distinct tell-tale signs are clusters of small distorted leaves near the tips of new growth. Zinc deficiency will result in a dramatic reduction in yield. Excess Zinc, although rare, leads to wilting and death.

So, how do you go about solving these issues?

Think of it like adding and subtracting. Plants like us have an intricate internal system that is constantly striving to achieve balance, and if any imbalance should occur it will begin to compensate for lower or excessive levels in attempts to reestablish equilibrium.

Reading both organic and nonorganic nutrient labels is essential. If you are having issues with too little Nitrogen for instance, find your choice of food that has a high number in N levels when looking at N-P-K values. When having trouble with deficiencies add the nutrient that is scarce. If your issue is with too much and your toxicity levels are high then flushing is the best solution. Remember to flush double the amount of water that your container can hold: 10 gals of water for a 5 gal container.

I hope you found this information to be useful, thanks for reading and as always… happy growing!