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Yellow leaves on cannabis. Why it happens & how to fix it!

Lucy Starley
May 10, 2024
11 min read
Yellow leaves on a cannabis plant.
Yellow leaves on a cannabis plant.
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Yellow leaves on your cannabis plants aren’t just an eyesore; they're a warning sign that your grow needs immediate attention. 

If you don’t take action, you could risk stunted growth, reduced product quality and yields and even plant death. 

In this post, we delve into the common reasons behind yellow cannabis leaves when growing indoors - from nutrient deficiencies to improper lighting. We’ll also offer proven solutions to restore your plants to perfect health. 

Whatever growth stages your plants’ are in, we’ve got the answers you seek. Equip yourself with the proper knowledge and ensure your cannabis thrives.

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

Stop yellow leaves on cannabis by learning to Grow the Best cannabis, join the newsletter now.

What causes yellow leaves on cannabis plants?

When you spot leaves turning yellow on cannabis plants, identifying the cause is the first step towards solving the problem. 

Several factors can lead to the yellowing of cannabis leaves, and each requires a different approach to remedy. Here’s a breakdown of the most frequent culprits:

Nutrient deficiencies

The most common issue is a lack of certain nutrients. Nitrogen deficiency, iron deficiency, potassium deficiencies and Magnesium deficiency are particularly notorious for turning cannabis leaves yellow. 

Nitrogen is vital for healthy leaf growth, iron is crucial for chlorophyll production, potassium helps with water regulation and photosynthesis, and magnesium plays a crucial role in photosynthesis, enzyme activation, and nutrient uptake.

Yellow leaves on cannabis due to a lack of magnesium.

Watering issues

Both overwatering and underwatering can stress your plants, causing their leaves to turn yellow. 

Too much moisture can cause root rot, which limits the plant's ability to absorb nutrients, while underwatering, especially in hot conditions, can quickly dehydrate your plant, making leaves dry and yellow.

Yellow leaves on cannabis due to a lack of water.

Light and heat stress

Cannabis plants need the right balance of light and heat to thrive. Grow lights that are too intense or an indoor setup that provides too much heat can bleach leaves and cause leaves to turn yellow. Cold shock can also turn your plants yellow or purple.

Monitoring the intensity and duration of light exposure, particularly in indoor setups, is crucial to prevent plant stress.

Yellow leaves on cannabis due to to much heat.

pH imbalances

The pH level of your soil or hydroponic setup greatly influences nutrient uptake and cannabis growth. 

An incorrect pH can lock out necessary nutrients, causing the leaves to turn yellow. Ensuring your growing medium has a pH between 6.0 and 7.0 is critical for optimal nutrient absorption. If you’re growing hydroponically, aim for a pH of 5.5 to 6.3 with 5.9 being perfect for coco.

By pinpointing the specific issue affecting your cannabis plants, you can take targeted action to correct it. 

Effective solutions and prevention of yellow cannabis leaves

Once you've identified why your cannabis leaves are turning yellow, the next step is to implement solutions that not only correct the current issues but also prevent future occurrences. 

Here’s how you can tackle each problem effectively:

Correcting nutrient deficiency

Nitrogen

Increase nitrogen levels using a balanced nutrient solution. Gradually introduce nitrogen-rich fertilisers to avoid nutrient burn.

An illustration showing the different stages of yellow leaves on cannabis due to a nitrogen deficiency.

Iron

Enhance iron availability by adjusting the pH level or using chelated iron supplements. This is especially beneficial in hydroponic setups to combat iron deficiency.

An illustration showing the different stages of yellow leaves on cannabis due to a iron deficiency.

Potassium

Apply a potassium-rich supplement if deficiency signs persist, ensuring not to overdose as it can lead to other nutrient imbalances.

An illustration showing the different stages of yellow leaves on cannabis due to a potassium deficiency.

Magnesium

Supplement with Epsom salts (magnesium sulfate) dissolved in water. Apply directly to the soil or as a foliar spray for rapid absorption.

An illustration showing the different stages of yellow leaves on cannabis due to a magnesium deficiency.

Regularly check plant health and adjust treatments as necessary to promote balanced nutrient levels and healthy cannabis growth.

A grower watering a cannabis plant.

Managing watering issues

Overwatering

Allow the top inch of soil to dry out before watering again, and ensure your pots have adequate drainage to prevent water accumulation. Fabric pots come in handy here by providing free drainage and additional aeration.

Underwatering

Establish a consistent watering schedule that keeps the soil slightly moist but not waterlogged. 

Use soil moisture meters to accurately gauge the need for watering and consider adding beneficial microbes to your soil.

An under watered cannabis plant with yellow leaves.

Adjusting light and heat

Light stress

If your plants show signs of light burn, consider raising your lights or reducing the intensity. Use timers to regulate exposure during critical growth phases.

Heat stress 

Maintain a stable environment with temperatures between 20°C and 28°C (or 30°C if supplementing with CO2). If temperatures rise above optimal levels, use fans or air conditioning to keep the air moving and cool.

Balancing pH levels

Regularly test the pH of your soil or nutrient solution and adjust accordingly using pH up or down solutions. This ensures nutrients remain available to your plants and reduces the risk of leaf yellowing due to pH imbalance.

Implementing these solutions will not only address leaves that have turned yellow but also enhance the overall health and productivity of your cannabis plants. 

By maintaining the right nutrient balance, watering regime, lighting setup, and pH levels, you’ll keep your cannabis looking green and vigorous.

Diagnosing yellowing leaves during different growth stages

The stage of growth your cannabis plant is in can significantly influence why the yellowing of the leaves is happening. Each stage has unique needs and potential issues. 

Here's how to diagnose and address yellowing leaves across different growth stages:

Yellow leaves on a cannabis seedling.

Seedling cannabis leaves turning yellow 

Common causes of yellowing leaves on cannabis seedlings and young plants include overwatering and nutrient burn. These are prevalent in seedlings due to their delicate nature.

To combat this, ensure seedlings are in a light, well-draining medium to avoid water retention. Start with a significantly diluted nutrient solution to prevent overwhelming the young roots.

Yellow leaves on cannabis on a large canna bis plant.

Cannabis leaves turning yellow during the vegetative phase

Yellowing leaves on cannabis plants during veg stage are often a product of a nutrient deficiency that becomes more apparent as plants grow. Nitrogen deficiency is typical, along with pH imbalances affecting nutrient uptake.

If this is the case, you’ll need to increase the nutrient supply carefully, focusing on nitrogen for leaf development. You should also regularly check and adjust pH to ensure nutrient availability.

A grower inspecting the yellow leaves on his cannabis plant.

Cannabis leaves turning yellow during the flowering stage:

Yellowing leaves on cannabis plants during flowering can be caused by light burn and nutrient lockout that can occur as plants focus energy on bud production. Potassium deficiency is also more common, impacting flower health and vigour.

To address yellowing leaves on cannabis during flowering, adjust lighting to prevent burn and ensure a balanced nutrient regimen that includes increased potassium. Monitor for signs of excess, as too much of one nutrient can lock out others.

It’s also worth noting that cannabis plants tend to naturally yellow towards the end of flowering. It’s a process called fading.

A flowering cannabis with yellow leaves plant fading.

General tips across all stages:

Regular monitoring

Keep a close eye on the overall health of your plants, checking for early signs of yellowing.

Adjust practices based on observation

Tailor your watering, feeding, and lighting based on your plants’ specific needs and responses at each stage.

By understanding each growth stage's unique requirements and common pitfalls, you can more effectively prevent and remedy yellowing leaves, ensuring your cannabis plants remain healthy and productive throughout their lifecycle.

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Identifying and addressing specific yellowing patterns on cannabis leaves

While general yellowing of cannabis leaves can indicate broad issues, particular patterns such as yellow spots, dots and tips provide more precise clues about your plants' health challenges. 

Recognising and treating these symptoms promptly can prevent further damage and ensure your plants recover more quickly.

A calcium deficiency on a cannabis plant.

Yellow spots on cannabis leaves

Yellow spots often arise from nutrient deficiency, particularly magnesium and calcium, or from fungal infections like leaf septoria.

Address nutrient gaps with a balanced supplement to combat yellow dots on cannabis leaves and ensure adequate calcium and magnesium levels. 

For fungal issues, improve air circulation and consider fungicidal treatments if necessary. Remember to remove and safely dispose of all infected foliage.

Besides nutrient issues and fungal pathogens, pests such as spider mites also cause small yellow spots on cannabis leaves due to their feeding.

Spider mides on a cannabis leaf.

Regularly inspect plants for pests and use organic pest control measures like neem oil or insecticidal soap to manage infestations.

Yellow leaves on a flowering cannabis plant.

Yellow tips on cannabis leaves

This is often a sign of nutrient burn, mainly when too much fertiliser has been applied.

To remedy this, flush the soil with plain water to reduce nutrient concentration and adjust future feeding to prevent over-fertilization.

Yellow leaves with brown spots on cannabis

This pattern can indicate a potassium deficiency, often coupled with overwatering.

Adjust watering practices to allow the soil to dry out more between waterings and supplement with a potassium-rich nutrient formula.

By closely monitoring these specific yellowing patterns and implementing the correct solutions, you can effectively address the root causes and help your cannabis plants maintain optimal health. 

Regular checks and balanced care routines are key to avoiding these issues and ensuring your plants thrive throughout their lifecycle.

Advanced tips for healthy cannabis plants

Ensuring your cannabis plants stay healthy and vibrant requires more than just addressing visible problems like yellowing leaves. Here are some advanced tips to enhance the overall health and productivity of your cannabis:

A healthy cannabis plant.

Enhance soil health

Soil growers should consider using organic compost or worm castings to improve soil fertility and structure. This will help increase nutrient availability and enhance moisture retention, providing a healthier growing environment for your plants.

A grower holding some soil next to a cannabis plant.

Optimal nutrient practices

Implement a well-balanced feeding regimen to ensure your plants get sufficient nutrients needed at each stage of growth. Avoid the common mistake of overfeeding, which can lead to nutrient burn and lockout, complicating yellow leaf issues.

Consider foliar feeding with micronutrients to ensure adequate nutrients, especially when root uptake issues arise. This can be particularly effective for quick corrections of minor deficiencies.

Preventative pest and disease management

Regularly apply organic preventive treatments like neem oil foliar spray to ward off pests and fungal diseases before they become a significant problem. This helps maintain the integrity of the plant's foliage, reducing stress and preventing yellowing leaves.

A vpd chat showing how to grow the best cannabis.

Environment control

Maintain optimal humidity, temperature and VPD levels to mimic the natural conditions in which cannabis plants thrive. Use dehumidifiers, fans, and heaters as necessary to keep conditions stable.

Ensure adequate airflow around all parts of your plants to prevent moisture accumulation, which can lead to fungal diseases and nutrient issues.

Regular monitoring and adjustment

Keep a detailed grow diary to track changes and tweaks made to your growing conditions. This information can help you pinpoint what works best and identify early signs of potential problems.

Adjust your care routine based on the plant’s response, fine-tuning elements like light exposure, water frequency, and nutrient ratios to optimise health and productivity.

By following these advanced tips, you address the yellowing of the leaves while building a robust foundation for your cannabis plants to thrive long-term.

Grow the best plants with the Grow Sensor.

Combat yellow leaves with the Grow Sensor

The Grow Sensor is a revolutionary tool for indoor growers. It offers precise monitoring and control over the growing environment, effectively combating yellow leaves. 

With its real-time environmental tracking capabilities, the Grow Sensor ensures that conditions such as temperature, humidity, and light levels are optimised to prevent common issues like root rot, nutrient deficiencies, light burns and poor air circulation.

By placing the Grow Sensor at the canopy level, you can receive instant insights into your plants' health and take proactive measures to address any potential problems before they escalate. 

The Grow Sensor's advanced sensor technology provides accurate data on crucial factors such as CO2 levels, leaf temperature, and VPD, helping you make informed decisions to maintain plant health.

Additionally, the Grow Sensor's light-level insights allow you to monitor light intensity and spectrum, ensuring that plants don’t receive too much light or too little. 

The Grow Sensor helps you ensure that your plants also receive the right quality of light from your light source to prevent stress, stunted growth, leaf drop and other symptoms. 

With optional soil probes, growers can also monitor soil moisture and temperature, preventing overwatering and promoting healthy root development.

The Grow Sensor's versatile connectivity and alerts enable you to always stay connected and informed about your growing environment. 

With long-range Wi-Fi connectivity and customisable alerts, you can receive notifications about any deviations from optimal conditions, allowing you to take immediate action to prevent yellow leaves and other issues.

The Grow Sensor is an essential tool for cannabis growers looking to combat yellow leaves and grow healthy plants. 

Its advanced features and precise monitoring capabilities empower you to create the ideal environment in your growing space, ultimately leading to healthier plants and higher yields.

Takeaways

Dealing with yellow cannabis leaves can be frustrating, but with the right knowledge and approach, it's a manageable problem. 

Throughout this post, we've explored the common causes of yellow leaves, from nutrient deficiencies and watering issues to light stress and pH imbalances. 

We've also provided you with effective solutions and advanced tips to correct these issues and prevent them from recurring.

Cannabis cultivation is both an art and a science. Every plant will communicate its needs differently, and yellow leaves clearly signal that your attention is needed. 

By applying the insights and strategies discussed, you can ensure that your cannabis plants remain healthy, vibrant, and productive.

Happy growing!

FAQs

What deficiency causes yellowing of leaves?

Yellowing of leaves, known as chlorosis, can be caused by several deficiencies, most commonly nitrogen, iron, magnesium, and potassium. Each deficiency affects the plant in specific ways and appears on different parts of the plant.

How do you fix yellow leaves on plants?

To fix yellow leaves on plants, identify the cause first - like nutrient deficiency, watering issues, or light stress. Then, adjust accordingly: increase the nutrient supply if deficient, ensure proper watering by checking soil moisture, and adjust light exposure to optimal levels. 

Regular monitoring and adjusting these factors can help restore leaf health.

Do yellow leaves mean overwatering?

Yes, yellow cannabis leaves can often indicate overwatering, especially if the leaves also feel soft and the soil is excessively damp. This condition can lead to root rot, which hinders the plant's ability to absorb nutrients effectively.

Can yellowing leaves be saved?

Yellowing leaves can sometimes be saved if the underlying issue is addressed early. Correcting factors like nutrient deficiency, improper watering, or lighting issues can help restore the leaves' health. However, severely damaged leaves may not recover and should be removed to focus the plant's energy on healthy growth.

How to tell if yellow leaves are from overwatering or underwatering?

To distinguish whether yellow cannabis leaves are from overwatering or underwatering, check the soil and leaf texture. 

Overwatered plants typically have soggy, waterlogged soil, and leaves may feel soft and limp. Underwatered plants have dry, crumbly soil, and the leaves usually feel dry and brittle.

Can yellow leaves become green again?

It's possible for some yellow leaves to regain their green colour under certain circumstances, such as addressing nutrient deficiencies or providing proper care. Action as soon as leaves starting to change colour is essential as it's generally more difficult once the leaves have fully yellowed. Early intervention and addressing the underlying issue are key to promoting healthier foliage.

Do yellow leaves mean my plant is dying?

No, yellow cannabis leaves do not necessarily mean your plant is dying. They are often a sign of stress or a condition that needs correcting, such as a nutrient deficiency, improper watering, or light issues. Addressing the underlying problem can help restore the plant's health.

Why are the bottom leaves on a cannabis plant turning yellow

The green leaves at the bottom of the plant often turn yellow due to nitrogen deficiency, as the plant prioritises sending nutrients to newer, upper leaves. 

It can also be a natural part of ageing, where older leaves lose their usefulness and fade. Ensuring adequate nitrogen levels and regular feeding can help prevent this issue.

Join the Grow The Best newsletter and never get yellow leaves on your cannabis plants!

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Lucy Starley
May 10, 2024
11 min read

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