Why Are My Cannabis Leaves Turning Yellow and How to Solve the Problem?

Ah, the eternal question that has perplexed cannabis growers for generations: Why do my marijuana leaves turn yellow? It’s a query I receive countless times, and the answer is never straightforward. A multitude of factors, such as nutrient deficiencies and lighting problems, can contribute to this issue. But worry not, fellow grower! Today, I will delve into the most common causes of yellow cannabis leaves, guiding you on how to diagnose, treat, and prevent this predicament. And as a bonus, I’ll share a secret trick that will revolutionize your plant health!

Understanding the Causes of Yellow Cannabis Leaves

Yellowing cannabis leaves are an indicator of an underlying problem, urging us to pay attention to our plants’ needs. However, it’s crucial to remember that yellow leaves are merely a symptom, requiring a deeper understanding to uncover the true issue at hand. Here are eight common reasons why your weed leaves may be turning yellow:

1. pH Imbalance

pH imbalances are prevalent among both novice and experienced growers and often manifest as yellowing leaves. This imbalance can affect even new growth, resulting in yellow or brown spots. Left untreated, it can lead to nutrient lockouts, depriving the plant of key nutrients and causing further complications. Testing for a pH imbalance is simple, using a pH meter or test strips. Cannabis plants thrive within a range of 6.0 to 7.0 for soil and 5.5 to 6.5 for hydroponics.

How to Treat pH Imbalance

Addressing a pH imbalance involves treating the growing medium to restore it to the optimal range. If the pH is too high, you can use a “pH down” product, gradually adding it to the water and growing medium until the desired pH is achieved. Conversely, if the pH is too low, a “pH up” product can be used likewise. Additionally, limestone is a common method for reducing soil acidity. To prevent future imbalances, regularly monitor pH levels and make adjustments as needed.

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Remember to use high-quality cannabis nutrients specifically designed for your plants.

Cannabis Leaves Turning Yellow

2. Temperature Issues

Temperature fluctuations can lead to curled and yellow cannabis leaves or, in some cases, leaves that turn purple. To ensure optimal growth, monitor the temperature within your grow room. Ideally, temperatures should range between 70-85°F (21-29°C) during the day and 60-70°F (15-21°C) at night.

Treating Temperature Issues

Treating temperature issues involves adjusting your heating, cooling, or ventilation system to maintain the desired temperature range. Additionally, consider the humidity levels within your grow room, as they can impact temperature. Use a dehumidifier or humidifier, if necessary, to maintain humidity levels between 40-60% during the vegetative stage and 40-50% during the flowering phase.

Temperature checking cannabis plants

3. Light Burns and Leaf Bleaching

Light burn is a common cause of yellowing cannabis leaves, often visible on leaves closest to the light source. If the upper leaves are turning yellow while the rest of the plant appears healthy, light burn is likely the culprit.

How to Treat Light Burn

Treating light burn is relatively simple. Adjust the distance between the light source and your plants or reduce the light intensity. If you have adjustable LED grow lights, lower the power output to prevent further damage. As a general rule, the more powerful the light, the greater the distance it should be from your plants. Use a light meter to measure light intensity in various areas of your grow space and adjust accordingly.

Cannabis light burn

4. Under and Overwatering

Both under and overwatering can lead to yellow leaves, a common mistake among beginner growers. Pay close attention to your plants’ water needs to prevent this issue.

How to Treat Under/Overwatering

Adjust your watering schedule to strike a balance in the amount of water your plants receive. If you consistently underwater, increase the frequency or volume of water. On the other hand, if you overwater, reduce the amount of water you provide. Take notes during the watering cycle, learning the perfect balance to avoid unnecessary stress on your plants.

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How to Prevent Under/Overwatering

Ensure your pots have good drainage and are appropriately sized for your plant’s growth stage. Avoid using pots that are either too large or too small, leading to watering issues. Transplanting your plants into suitable containers is crucial for their well-being.

Under watered cannabis plant

5. Root Rot

Consistent overwatering can result in root rot, causing cannabis leaves to turn yellow, wilt, and eventually die. Checking your plant’s roots is essential to identify this issue. Healthy roots should appear white or light tan in color. Unhealthy roots suffering from root rot, however, will be dark brown or black with a mushy texture and possibly an unpleasant odor.

How to Treat Root Rot

Early detection is key when it comes to root rot. Once identified, you must remove the affected roots entirely. Carefully lift the plant from its container and wash off the soil. Use clean scissors or a pruning tool to cut away dark and mushy roots. Transplant your cannabis plant into a clean pot with well-drained soil, ensuring only healthy roots remain. Consider using beneficial microbes, such as Amplify, to promote root health and ward off future root rot.

Root rot in cannabis plants

6. Pest Invasion

Pests are notorious troublemakers, causing yellow leaves by sucking the sap out of cannabis plants. Spider mites, aphids, and whiteflies are the most common culprits.

How to Treat a Pest Invasion

Dealing with pests requires prompt action, as they can devastate entire crops. Begin by removing heavily infested plants from your grow room. Next, eliminate damaged leaves and apply an organic pesticide or insecticidal soap to the plant, following the instructions carefully. After removing the pests, maintain a clean grow space and monitor your plants closely for any signs of a new infestation. Regularly inspect the undersides of leaves and the growing medium for eggs or larvae.

Pests on cannabis plant

7. Leaf Septoria

Leaf septoria, also known as yellow leaf spot, is a fungal disease responsible for yellowing cannabis leaves. It typically begins as small, circular yellow spots on lower leaves, eventually turning brown with a yellow halo. If left untreated, leaf septoria can spread throughout the entire plant, leading to irreversible damage.

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How to Treat Leaf Septoria

To combat leaf septoria, remove all affected leaves to prevent the fungus from spreading. Then, apply a fungicide, typically a copper-based product, to control the infection.

How to Prevent Leaf Septoria

Maintaining good airflow and proper humidity in your grow room is crucial, as fungus thrives in moist environments. Avoid wetting the leaves while watering and regularly sanitize your tools and hands to minimize the chances of infection.

Leaf Septoria

8. Over/Under Fertilization

Over and under-fertilization are common mistakes, particularly among beginner growers. As you gain experience, you’ll become more adept at identifying nutrient imbalances. However, less experienced growers may encounter this issue during their initial grow cycles.

How to Treat Fertilization Issues

First, determine whether you’ve over or underfed your plants and which essential nutrient is imbalanced. Adjust your nutrient regimen accordingly to rectify the issue. For more information on identifying and addressing nutrient deficiencies, refer to our detailed guide.

Potassium Deficiency in cannabis plants

When Should You Not Worry About Yellow Cannabis Leaves?

Yellow leaves are a natural part of a plant’s lifecycle, so don’t fret at the first sight of yellowing. During the vegetative phase, fan leaves often turn yellow. Additionally, leaves may yellow during the flowering phase as the plant reallocates energy toward bud and seed production instead of photosynthesis. If the yellowing is limited to lower, older leaves, and the rest of the plant appears healthy, there is no cause for concern. This natural process occurs in every plant’s life cycle.

Your Secret Weapon

Amplify is your secret weapon for thriving as a grower. Enriched with highly concentrated and naturally occurring plant growth-promoting rhizobacteria, Amplify enhances nutrient and water uptake while safeguarding your plants’ rhizosphere from harmful pathogens. Our full-spectrum microbial inoculant is up to 3X more effective than competing brands, significantly improving nutrient absorption, increasing yields, and maximizing your plants’ genetic potential.

Buy Amplify here

Ready to tackle nutrient deficiencies? Check out our comprehensive guide.

With these insights and solutions, you can say goodbye to yellow cannabis leaves and cultivate healthy, thriving plants. Happy growing!