5 Common Cannabis Leaf Symptoms and Solutions

Cannabis plants, like all living things, communicate their needs in various ways. One of the most visual is through their leaves. Regular checks on your plants are crucial to catch early signs of cannabis leaf problems, which can indicate several deeper issues or deficiencies.  

When growers notice strange colors or patterns on their leaves, it signals that the plant might be lacking something essential or is under stress. This article dives into common cannabis leaf problems, focusing on the story told by the color changes we can observe. For a deeper understanding of plant nutrition, check out our comprehensive guide on 18 cannabis nutrients.

Different types of leaves

Before we dive into the color symptoms, let’s clarify the two main types of leaves we’ll discuss: fan and sugar leaves. Fan leaves are the large, iconic leaves that act as the plant’s solar panels, capturing sunlight for photosynthesis. Sugar leaves are smaller, often found closer to the buds, and have a sugary appearance due to the trichomes covering them. Understanding these leaves’ roles is key when identifying deficiencies impacting your cannabis plant.

Yellow leaves are a sign of several possible issues

There are many reasons why your plant’s leaves could be turning yellow. If you pay attention in the garden, you can determine whether the color change is being caused by you, pests, or the natural fading of the plant as it nears the end of its life.

Nutrient deficiency

One of the most common nutrient deficiencies that cause yellowing of the leaves is nitrogen deficiency. Nitrogen is needed in large amounts during vegetative growth; if your fan leaves are turning yellow during veg, there’s a good chance your plants need more Nitrogen. 

This mineral is needed in abundance and is very mobile in the plant, soil, and water, which means it can wash out of your medium easily. This also means it’s easy to replace in your plant and can be fixed with a simple fertilizer application such as fish powder. You can use a simple NPK strip test to determine if your plant is deficient in Nitrogen, Phosphorus, or Potassium.

Watering issues

Watering issues are the home gardener’s biggest problem and cause a cascade of other cannabis plant problems. Not watering enough can cause a deficiency in nutrients since water is the primary way plants take up nutrient solutions. 

Overwatered soil can cause root rot, a fungal pathogen that causes the yellowing of the leaves and even plant death. Using a moisture meter, like a tensiometer, that monitors the pressure within the soil can help maintain optimal moisture levels. Alternatively, you can squeeze a handful of soil—if water comes out, the soil is oversaturated.

Pest problems

Several pests, such as mites, can cause physical damage to your leaves, which may result in yellowing. You can prevent this from happening by regularly monitoring your plants for pests and spraying them preventatively with essential oils, such as peppermint, oregano, and thyme. If you do get pests, a simple foliar spray of soapy water, alcohol, horticultural oil, and essential oils can help knock back pest pressure.

Light burn

Sometimes, leaves turn yellow when growing too close to artificial grow lights; leaves may droop and burn if this happens. This type of yellowing can be prevented by raising your lights or growing smaller plants by flipping them into flower when they are smaller. You can also train your plants to grow under netting using the SCROG (screen of green) method to keep them from growing too close to your lights.

Brown leaves can indicate a few issues

Mitigating the range of browning issues involves adjusting nutrient concentrations, pest management strategies, and creating an optimal growing environment.

Nutrient burn

Also called “nute burn,” this cannabis leaf problem comes from excessive feeding or nutrient deficiency and can cause browning of the leaves beginning at the tips. Provide your plant with an all-purpose fertilizer like Earth Juice Rainbow mix, which contains a wide variety of minerals. Remember, soil testing before adding nutrients is always a good idea.

Pests or disease

Pathogens and pests can cause leaf damage and cause leaves to turn brown. Heavy infestations of mites or fungal pathogens such as botrytis, also known as bud rot, can also cause browning or septoria, which causes brown spots on weed leaves.

You must determine the type of pest before treating any symptoms. Once you have figured that out, you can utilize an integrated pest management plan to treat and prevent any further infestations.

Environmental stress

Harsh conditions, such as too much cold or heat stress, can lead to problems. If temperature extremes cause severe wilting in your plant leaf tips may end up turning brown and dying. You can solve this issue by controlling your indoor environment with air conditioning and ensuring there is enough water. 

If the temperature gets too high, water evaporates quickly, which may result in your plant wilting and browning. If you’re growing outdoors and temperatures are dropping below freezing, consider throwing a frost tent over your weed plant or chopping it down early.

Orange/Rust leaves are often associated with

Nutrient deficiencies

Lack of required inputs, particularly phosphorus, may result in an orangish color on parts of the plant. Although rare, this can happen and can be prevented by using micronized rock phosphate.

Temperature drops 

Overly cold conditions can also cause this color change. Cold temperatures can affect a plant’s ability to produce chlorophyll, which is what produces the green pigment. When chlorophyll stops being produced, leaves may change a variety of colors, including orange. You cannot do anything about this if you are growing outdoors, and this rarely occurs indoors.

Rust Fungi 

This fungus can cause orange spots on cannabis leaves. Check your humidity levels and use sulfur spray during vegetative growth to reduce fungal infections.

White cannabis leaves can mean

Powdery Mildew

This is a fungal pathogen that manifests in white powdery spots on your leaves. This can be treated with citric acid in a water solution and sprayed on your plant.

Genetic variegation

This is less common but naturally occurs in some strains. It simply means the discoloration is genetic and not necessarily a sign of illness. However, all other issues should be assumed before this.

Viral Infections 

Illness can prevent chlorophyll from being produced. Remove infected plants after harvesting and do not use clones from that plant. Make sure to sterilize all tools used on a marijuana plant and remove the soil it was growing in.

Black leaves may be a serious sign of trouble

Necrosis

When plant leaves turn black, it indicates necrosis, meaning the affected tissue is dead and can no longer support growth. Promptly remove the damaged leaves.

Bud rot or fungal infections 

To save the plant, the affected leaves must be removed immediately, and environmental factors, such as humidity, must be adjusted to ensure ideal conditions for the plant’s life stage.

Severe nutrient burn

If this occurs, flushing with water can help remove some of the excessive nutrients.

Additional Considerations for Plant Health

Beyond the color changes in leaves, other signs and preventive measures can significantly impact the success of your cannabis grow. From the pH of your soil and water to the plant’s natural tendencies, from genetics to pests, there are always things you can learn more about to improve your garden and the overall health of your plants.

Soil Health and pH Levels

Soil health is fundamental to nutrient availability. A balanced soil pH ensures that nutrients are readily available to the plant. Cannabis prefers a slightly acidic pH range of 6.0 to 7.0 in soil and 5.7 to 6.2 in hydroponic setups. Regularly testing your soil or medium’s pH can prevent a nutrient lockout, a condition where plants cannot absorb nutrients efficiently, often leading to various symptoms, including the yellowing or browning of leaves.

Understanding Plant Genetics

Different cannabis strains have varying resilience to stress, nutrient requirements, and susceptibility to pests and diseases. Selecting strains that are well-suited to your growing environment can greatly reduce the risk of common problems. Some strains naturally exhibit colors other than green, especially near harvest time. Understanding the genetic predisposition of your plants can help you distinguish between normal and concerning symptoms.

Integrated Pest Management (IPM)

An Integrated Pest Management (IPM) plan combines biological, cultural, physical, and chemical tools to manage pest populations. This may include introducing beneficial insects to control pest populations and applying organic pesticides, like neem oil, as a last resort. Regularly inspecting your plants will allow for the early detection and management of pests before they become a significant problem.

Educating Yourself Continuously

The world of cannabis cultivation is ever-evolving, with continuous research and advancements in growing techniques. Staying informed through reputable sources, forums, and cultivation communities can provide you with the latest insights and innovations in cannabis care. Education is a powerful tool in preventing and solving cultivation challenges.

Cannabis Leaf Problem FAQs

What causes brown spots on cannabis leaves?

Brown spots are typically caused by nutrient deficiencies, particularly calcium and magnesium, or by pH imbalances hindering nutrient uptake. Brown spots can also be a sign of fungal infections like septoria.

Will cannabis leaves get you high?

Cannabis fan leaves contain minimal THC compared to the flowers. While they have some cannabinoids, they are not potent enough to produce significant psychoactive effects. Sugar leaves, on the other hand, are covered in trichomes that contain cannabinoids and may get you high.

Can cannabis plants catch a virus?

Yes, cannabis plants can be affected by viruses, which can lead to stunted growth, discoloration, and leaf curling. Good hygiene practices are essential to prevent viral infections. Buying from reputable breeders and starting from seed reduces your chances of growing an infected plant.

What’s the most common symptom of a cannabis leaf problem?

Yellowing leaves are among the most common symptoms, often indicating issues with watering, nutrition, or lighting.

By understanding these common cannabis leaf problems and solutions, growers can better care for their plants, ensuring a healthy and productive grow. Remember, the key to success lies in regular observation and timely intervention to prevent problems.