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Diagnosing Cannabis Nutrient Deficiencies in Sick Plants

September 23, 2016

The secret to growing great cannabis isn’t really a secret at all; provide your plants with adequate light, a suitable climate, the right amount of water, and proper nutrients, and you will have healthy plants capable of fighting off most pests and diseases.

When plants do not receive the correct level of nutrients, they become stressed and more susceptible to bugs, mold, and other pathogens. Their growth may also be stunted, resulting in reduced yields. Knowing the signs of nutrient deficiency is a vital skill for budding cannabis growers, so let’s take a look at all the essential nutrients, the symptoms associated with their absence, as well as other factors in potential deficiencies.

Getting the Right pH for Your Cannabis Plants

Use a pH Soil Test Meter for cannabis plants

Plants can only absorb nutrients through their roots if the growth medium or hydroponic solution is at the correct pH. If conditions are too acidic or too alkaline, certain nutrients become unavailable to the root system. Over-fertilizing your plants can quickly lead to pH problems and nutrient lockout, showing symptoms that are easily mistaken for a nutrient deficiency to the untrained eye.

Before attempting to diagnose any nutrient deficiency, be sure that the pH of your soil, medium, or hydroponic solution is within the acceptable range. For soil and soil-like media, the range is 5.8 to 6.8, with 6.3 considered optimum. The proper range for hydroponic solutions is 5.5 to 6.5, and most brands of hydroponic nutrients will indicate an ideal level for their product. Testing the pH of your water is also recommended, as it can vary widely depending on the source.

“Mobile” and “Immobile” Nutrients

Man hold a soil in his hands.

Nutrients are classified as mobile or immobile depending on whether they can be translocated once they have been fully assimilated by the plant. A mobile nutrient stored in the older leaves of the plant can be moved to solve a deficiency in another part of the plant. Immobile nutrients will remain very close to where they were initially deposited.

Mobile nutrient deficiencies will show symptoms in the older leaves at the base of the plant, while immobile nutrients will show the first signs of deficiency in the newer growth at the top and outer branches of the plant. Knowing which nutrients are mobile and which are immobile will help you diagnose potential deficiencies.

Essential Cannabis Nutrients and Symptoms of Deficiency

Essential nutrients for Marijuana plants and symptoms of deficiency
Your plant needs several essential nutrients, so be sure to keep an eye on these signs and visual cues that could indicate a potential deficiency.

Nitrogen (Mobile)

The most common nutrient deficiency in cannabis, nitrogen is essential throughout the lifecycle of the plant, but especially during vegetative growth.

Nitrogen Deficiency Symptoms:

  • An overall lightening and then yellowing in older, mature leaves, especially near the base of the plant
  • Severe deficiency will see continued yellowing, progressing up the plant, with possible discoloration and brown spots at leaf margins; eventually leaves curl and drop
  • Decreased bud sites and earlier flowering with substantially reduced yields
Related

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Phosphorous (Mobile)

Phosphorous is essential for photosynthesis and the release of stored energy in carbohydrates. While deficiency is uncommon (usually developing due to pH being above 7.0), the result can be catastrophic for young plants, and lead to stunted growth, delayed flowering, low yields, and poor resin production in mature plants.

Phosphorus Deficiency Symptoms: 

  • Purpling of the petioles (leaf stems) on older leaves, followed by leaves taking on a dark blue-green hue
  • As deficiency progresses, both upward and outward growth slows drastically, blackish-purple or dark copper colored spots appear on leaves, and dead spots develop on petioles while leaves curl and drop
  • Sometimes leaves turn metallic purple or dark bronze in color
Related

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Potassium (Mobile)

Crucial to the production and movement of sugars and carbohydrates, potassium is also indispensable to the process of cell division as well as transpiration, root growth, and water uptake. Simply put, without it plants can’t grow. Deficiency leads to increased internal temperatures in the foliage of the plant, which causes the plant to evaporate more moisture through its leaves to cool down.

Potassium Deficiency Symptoms:

  • Dull, overly green leaves, followed by “burnt” rusty-brown leaf tips, chlorosis (yellowing), and brown spots, particularly on older leaves
  • Further deficiency shows in leaf burn, dehydration, and curling of younger growth
  • Left unchecked, potassium deficiency will result in weak plants, high susceptibility to pests and disease, and drastically reduced flowering
Related

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Calcium (Immobile)

Essential to cell integrity and growth, calcium aids the flow of nitrogen and sugars through the plant. Deficiency is usually found in hydroponic gardens or outdoors in very wet, cool climates with acidic soil.

Calcium Deficiency Symptoms:

  • Lower leaves curl and distort, followed by irregular brownish-yellow spots with brown borders that grow over time
  • Root tips will start to wither and die, and the plant will become stunted with decreased yields

Related

How to Grow Hydroponic Cannabis

Magnesium (Mobile)

Magnesium is the central atom in every molecule of chlorophyll, meaning that plants use it in very high amounts. It is crucial for absorbing energy from light, as well as helping enzymes create the carbohydrates and sugars that produce flowers.

Magnesium Deficiency Symptoms:

  • Plants will not show signs of a magnesium deficiency until 3 to 6 weeks after it has begun, at which point you’ll see the areas between the veins of older leaves turn yellow (interveinal chlorosis) and the formation of rust colored spots
  • These symptoms will progress through the whole plant, with more and larger spots developing in the interveinal areas as well as tips and margins of leaves
  • Some leaves will curl, die, and drop, while the whole plant looks sickly and droopy
  • Symptoms of magnesium deficiency will quickly escalate during flowering, leading to a reduced harvest
Related

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Sulfur (Semi-Mobile)

Essential to plant respiration and the synthesis and breakdown of fatty acids, sulfur plays a huge part in the production of oils and terpenes. It is uncommon to see a sulfur deficiency in cannabis, but these deficiencies are usually the result of a loss of phosphorous due to a high pH level in the root zone.

Sulfur Deficiency Symptoms:

  • Look for young leaves to turn lime green then yellow with stunted growth, followed by the yellowing of leaf veins accompanied with drying and brittleness
  • Continued deficiency results in slow, weak flower production with lowered potency

Related

What are cannabis terpenes and what do they do?

Copper (Semi-Mobile)

Needed only in trace amounts, copper aids in nitrogen fixation, carbohydrate metabolism, and oxygen reduction.

Copper Deficiency Symptoms:

  • Deficiency is very rare, and first symptoms are seen in the slow wilting, twisting, and turning of new growth
  • Dead spots appear on leaf tips and margins, and sometimes the whole plant wilts
Related

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Iron (Semi-Mobile)

Iron is essential for nitrate and sulfate reduction and assimilation, and a catalyst for chlorophyll production. Deficiencies are usually the result of improper pH levels or excess levels of manganese, zinc, or copper.

Iron Deficiency Symptoms:

  • Initial symptoms appear in younger growth, with interveinal chlorosis showing at the base of new leaves
  • Symptoms then progress through the leaves and into older growth, with overall yellowing between leaf veins
Related

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Manganese (Immobile)

Manganese helps utilize nitrogen and iron in chlorophyll production as well as aiding in oxygen reduction. Deficiency is rare and usually caused by high pH or an excess of iron.

Manganese Deficiency Symptoms:

  • As with other immobile nutrients, symptoms start in the new growth, initially showing interveinal chlorosis followed by necrotic spots, gradually spreading to older leaves
  • The most obvious sign is when leaf margins and veins remain green around the yellowing of the interveinal areas
Related

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Molybdenum (Mobile)

A player in two major enzyme systems that convert nitrate to ammonium, molybdenum is used by cannabis in very small amounts. Deficiencies are rare and can occur as the result of cold weather.

Molybdenum Deficiency Symptoms:

  • Older leaves yellow, sometimes developing interveinal chlorosis and discoloration at leaf edges
  • Eventually leaves cup and curl up before twisting, dying, and dropping
Related

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Zinc (Immobile)

Zinc is crucial for sugar and protein production, as well as in the formation and retention of chlorophyll and for healthy stem growth. Deficiency is quite common, especially in alkaline soils and dry climates, and is usually the result of high pH levels.

Zinc Deficiency Symptoms:

  • Young leaves and new growth exhibit interveinal chlorosis, with small, thin leaf blades that wrinkle and distort
  • Leaf tips will discolor and burn, followed by leaf margins and then brown spots
  • The most obvious sign is leaves that turn 90 degrees sideways

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  • potmaster

    The only thing is that most soil is deficient in Calcium. 50% of Plant’s needs are fulfilled by Calcium. For every inch in diameter a plant one needs one pound of Calcium. (bone meal). Remember when one harvests and removes the plant one has removed nutrients from the soil. When adding nutrients to the soil, if the percentage of that ingredient is 0.05% disregard. Some suppliers will put anything they can find to put on their label. If you want to grow strong healthy plants understand the demands of the plant and the soil in which you are planting.

  • $parkle Puss

    So what happens if there’s a severe, uncorrected nitrogen deficiency early in flower? Will the buds themselves eventually turn yellow & die like the leaves? They seem to fight really hard to stay green, as do the bud sites around them. I can’t find a single picture of what I’m looking for online.

    I know N deficiency is normal in LATE flowering, but I keep having my whole plant turn yellow overnight in Week 1 of bloom. Just wondering what the end result would be if this wasn’t corrected at all. Would you have to harvest early or could the plant continue growing even if all the leaves fell off & there was nowhere else to pull nitrogen from?

    • Thomas kelly

      There are too many factors we do not know about your grow by your description to be of any help. What is your medium, feeding, temperatures, watering schedual, humidity, light, ect? Without these perimeters all we can do is guess. I have seen similar symptoms to what you describe when a person doesn’t increase the amount of water during flowering as plants are doubling in size. A plant that doubles in size would obviously need twice as much water. Under watering them can dry out the roots and cause them to die back resulting in nutrient deficiencies.

    • makenzie

      Leaves will die off buds may not be a good as healthy plant as a lot of energy for budding comes from leaves. Buds will be smaller as nitrogen is a main part in plant stem growth and lower nitrogen is weaker stems weaker stems means smaller buds a main part of the light is converted into energy from the leaves themselfs. The leaves should be non papery feeling smooth soft feeling with a dark forest green color to them.

  • Cain Kent

    Your nutrient concentration is probably a little to high, the plants are drinking the water and nutrients but there is leftover nutrients in your drain solution so the ppm would be higher

  • Cain Kent

    When is a good time to start adding nutrients to my dwc setup? Plants are about 3 weeks old

  • Cwhizard

    Have yellowing on the leaf edge, no interveinal chlorosis. Plant is growing in a food safe plastic bucket, 100% miracle grow potting soil, and is cocropped with ladino white clover, which is also starting to yellow. There are a few earthworms in the soil, I put 2 in there. Seems like a butrient deficiency rather than toxicity because of the clover also yellowing. But coudl be toxicity of some kind.

    • Lorraine Smith

      I’ve got the same issue. Northern lights autos in coco. Thought it might be zinc deficiency, but could be lockout. Did you get yours sorted?

  • makenzie

    It could be mineral build up in soil from using tap water or undistilled water or to much nutrient and it’s building up in soil watch for black leaves as a sign of nutrient burning usually started at bottom when I ran into problem but may start from top and look like light burning. I usually give a good water with lot of runoff for 1 to 2 weeks and go back to feeding scheduale. Make sure you have good air movement in space to prevent molding or bacterial growth on soil wile doing the flush as soil may take longer to dry through.

  • wilfredo ocasio

    I need help with my babe 😫😞😭

  • wilfredo ocasio
  • Karen Stafford

    I have 10 Triple Threat plants in 5 gallon containers what are approximately three and a half months old. They are loaded with buds that look very green and healthy. They were oing fantastic until about a week ago when the older leaves begin to turn yellow get brown spots and then curl up and fall off. Is it an iron deficiency?