Cannabis Leaves Warn You About The Health Of The Plant

Philip Ghezelbash June 15, 2019 0 comments

These are all the things to watch for on your cannabis leaves.

The color, texture, and appearance of cannabis leaves can tell growers a lot about the health of a cannabis plant. Experienced growers carefully monitor cannabis plant leaves to determine what a plant needs.  The appearance of leaves can tell us whether a plant has issues with fungus, pests, and nutrient deficiencies.

We’ve outlined a few of the main issues that can be found in cannabis plants. If you’re starting your own home grow, knowing the issues to look out for is crucial to getting the most out of your limited plant allowance.

Varieties of Nutrients for Cannabis Plants

All plants require a range of nutrients for sustainable growth. Nutrients are classified as either mobile or immobile. A mobile nutrient can move freely from one place to another within the plant. Mobile nutrients translocate throughout the plant to compensate for a nutrient deficiency in another area of the plant.

The type of soil you use is crucial for your plant. Many of these deficiencies can be solved with mineral-rich soils and additions of mineral additives. Here are a few crucial nutrients and the way to recognize their deficiencies.

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Mobile nutrients:

Nitrogen deficiency is the most common nutrient deficiency. A lack of nitrogen causes lightening and yellowing of leaves. 

Magnesium deficiency doesn’t show itself for 3-6 weeks. A lack of magnesium causes veins of older leaves to turn yellow. Over time, larger spots will develop before the leaves begin to curl and die.

Potassium is vital for the transport of glucose (sugar), as well as for cell mitosis, root growth, and water uptake. A potassium deficiency will turn leaves dull green, cause brown discoloration on leaf tips, and dehydrate the plant.

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Phosphorous is vital for photosynthesis and for releasing energy stored in glucose. A lack of phosphorus results in black-purple spots on leaves.

Molybdenum is essential for the function of two enzymes converting nitrate to ammonium. A molybdenum deficiency will cause older leaves to turn yellow and discolor at leaf edges before dying.


Iron helps leaves produce chlorophyll (the backbone of photosynthesis). Excessively high mineral concentrations of zinc or copper and imbalanced PH levels lead to iron deficiency. Iron deficiency will cause yellowing between leaf veins and a loss of normal chlorosis (green color) at the base of new leaves.

Copper is only required in small amounts but it’s essential for glucose metabolism, and for converting nitrogen in the air into ammonia. Copper deficiency will cause the slow wilting and twisting of leaves.

Sulfur is essential for plant respiration. This nutrient is also crucial for producing oils and terpenes with medicinal value. Sulfur deficiency causes leaves to turn light green and eventually become dry and fragile.

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Zinc is essential for sugar and protein production. A zinc deficiency will cause new leaves to wrinkle, abnormal growth patterns, and leaf tip discoloration.

Manganese helps plants utilize nitrogen and iron for the production of chlorophyll. Manganese deficiency results in chlorosis between veins and then the death of leaf cells.

Calcium is essential for the growth and strength of cells. Calcium deficiency causes leaves to curl and form yellow-brown spots.

Fungal Infections in Cannabis Leaves

Fungal outbreaks in grow rooms are commonly caused by a range of factors such as poor air circulation, humidity alterations, overcrowding of cannabis plants, temperature changes, and infected seedlings or clones. Pests can also proliferate fungal diseases, as well as other contaminates spread by equipment and grower’s clothing. Here are a few fungal infections to look out for.

Fusarium is a fungus that comes from soil. This fungus blocks nutrient delivery to the cannabis plant. Fusarium causes dark spots to appear on lower leaves, which quickly turn yellow or brown as the leaves die.

Verticillium is a wilting pattern that is caused by a fungus with similar traits to fusarium. Chlorosis appears at the bottom of the plant, causing yellowing of leaves. Chlorosis occurs in the veins and leaf margins first. These leaves will darken and wilt.

Bud rot causes the internal rotting of cannabis flowers, but it frequently starts in the leaves. This fungal infection will appear as a white fuzz at the bottom of leaves and eventually turn yellow.

Powdery mildew appears as a white or grey powder-like substance on cannabis leaves. Powdery mildew starts at the base of cannabis plants and moves up over time.

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Pest Infestations in Cannabis Leaves

Pests make leaves their humble home. Leaves serve as a form of environmental protection and as a source of sustenance for pests. But they’re hardly what you want in your home grow. There are many different types of cannabis pests. Below are three of the most common ones found on cannabis leaves.

Spider mites are a small oval bug with six to eight legs. Spider mites damage leaves by eating away at the chlorophyll, leaving behind white or yellow spots.

Fungus gnats are small black bugs about three to five millimeters in size. Fungus gnats don’t eat leaves or flowers; instead, fungus gnats damage roots. Females lay eggs within the soil surrounding the cannabis plant, causing damage to roots. This causes the cannabis plant to become more susceptible to infestations.

Aphids are small yellow bugs with wings that live under cannabis leaves. These bugs reproduce rapidly, and so infestation growth tends to be exponential. Aphids extract nutrients from leaves, causing the leaves to develop a yellow color.

Vulnerable to Pests, Fungus, and Nutrient Deficiencies?

Both indoor and outdoor crops leave cannabis plants susceptible to pests, fungus, and nutrient deficiencies. Indoor plants in a greenhouse tend to be a better option for pest management as the environment is easily controlled. At the same time, however, an infestation indoors can be more conducive to widespread crop failure due to the proximity of plants to one another. The first thing you want to do upon finding a pest or fungus infestation is to remove the infected plant to prevent spread. 

As a grower, looking out for the discoloration of leaves is one of the best ways to spot signs of fungus, pests, and nutrient deficiencies. The tricky part is to pinpoint precisely what’s causing these discolorations and abnormalities. Once you have, you can easily rectify the issue.

Author avatar

Philip Ghezelbash
Philip Ghezelbash is an ex-personal trainer with a science background who currently operates New Zealand's only health specialized writing studio. He is passionate about presenting complex science in an easy to digest manner and is a firm believer that cannabis has substantial potential to be used as a medicine for degenerative disease.