Why & How to Fix Leaves Turning Yellow During Flowering

Causes & Solutions of Cannabis Leaves Turning Yellow During Flowering

Yellowing leaves, often referred to as “chlorosis,” in cannabis plants during the flowering stage can be concerning for growers. Understanding the various causes behind this issue is essential for effectively addressing and preventing it. Here are the primary factors that can lead to yellow leaves during the flowering phase:

1. Nutrient Deficiency

Nutrient deficiency, such as Cal-Mag deficiency,  is the most likely cause of yellowing leaves in cannabis plants. During the flowering stage, the demand for nutrients, particularly nitrogen (N), phosphorus (P), and potassium (K), increases significantly. If the plant does not receive an adequate supply of these essential nutrients, it can result in chlorosis.

image source: growlightinfo.com

Solution: To prevent nutrient deficiency, use a well-balanced fertilizer specifically formulated for cannabis during flowering. Regularly monitor nutrient levels and adjust the feeding regimen as needed.

2. pH Imbalance

The pH level of the growing medium is crucial for nutrient uptake. When the pH is too high or too low, it can lead to nutrient imbalances, preventing the plant from absorbing the necessary elements properly.

Solution: Regularly test and adjust the pH of your growing medium to maintain an optimal range (typically between 6.0 and 7.0) for nutrient uptake.

3. Overwatering or Underwatering

Inconsistent watering practices can stress cannabis plants, leading to yellowing leaves. Overwatering can suffocate the roots and reduce their ability to absorb nutrients, while underwatering can cause drought stress.

Solution: Water your cannabis plants according to their specific needs, allowing the soil to dry slightly between waterings. Using well-draining soil and pots with proper drainage can help prevent overwatering.

4. Light Stress

Cannabis plants are sensitive to light intensity and spectrum. Excessive heat, intense light, or prolonged exposure to ultraviolet (UV) rays can lead to stress and leaf discoloration.

Solution: Maintain appropriate light levels, ensuring that your grow lights are positioned at the correct distance from the plants and that the temperature in the growing environment is within the optimal range.

5. Pests and Diseases

Insects, fungi, and other pathogens can damage cannabis foliage, causing leaves to turn yellow. Pests like spider mites and diseases like powdery mildew are common culprits.

Solution: Implement a robust pest management strategy, which may include regular inspections, using beneficial insects, and maintaining a clean and well-ventilated growing area. If a disease is detected, treat it promptly with appropriate remedies.

6. Genetic Factors

Some cannabis strains are inherently more prone to developing yellow leaves during flowering due to their genetic makeup. This can be influenced by factors such as strain lineage and breeding.

Solution: If you’re experiencing consistent yellowing in a particular strain, consider switching to a different strain with more suitable genetics for your growing conditions.

7. Environmental Stressors

Environmental factors such as extreme temperatures, humidity fluctuations, and poor air circulation can stress cannabis plants, leading to leaf discoloration.

Solution: Create a stable and controlled growing environment, maintaining suitable temperature and humidity levels, and ensuring adequate air circulation and ventilation.

By identifying the specific cause of yellowing leaves in your cannabis plants during flowering and implementing the appropriate solutions, you can promote healthy growth and vibrant buds, ultimately maximizing your harvest.

How to Prevent Leaves from Turning Yellow During Flowering

Although nutrient deficiency is the biggest culprit for cannabis leaves turning yellow, it’s, unfortunately, the most difficult one to trace. Therefore, in addition to providing proper nutrients to your cannabis, there are other measures you can take to prevent leaves from turning yellow during flowering. 

Balanced Nutrient Management

• Microelement Awareness: Besides the primary nutrients (N-P-K), pay attention to microelements like magnesium (Mg), calcium (Ca), and iron (Fe). These micronutrients play essential roles in plant health and can help prevent yellowing leaves.
• Leaf Analysis: Conduct regular leaf analysis to assess nutrient levels. It provides a precise snapshot of your plant’s nutrient status and helps fine-tune your feeding regimen.
• Organic Amendments: Consider incorporating organic soil amendments like compost, worm castings, or bat guano. These can provide a slow release of nutrients and improve soil health over time.

pH Monitoring and Adjustment

• Buffer Solutions: Use pH buffer solutions to stabilize pH levels in your growing medium. These solutions can help maintain a consistent pH environment, reducing the risk of nutrient lockout.
• Reservoir Management: If you’re using hydroponics or soilless mediums, monitor and adjust the pH of your nutrient reservoir regularly. Fluctuations in pH can affect nutrient availability.

Proper Watering Practices

• Drip Irrigation: Consider using drip irrigation systems with adjustable flow rates. This allows you to control the amount of water each plant receives, reducing the risk of overwatering or underwatering.
• Watering Techniques: Water the base of the plants directly rather than overhead to minimize moisture on leaves. Wet foliage can increase the likelihood of fungal issues.
• Root Health: Maintain healthy root systems by providing adequate oxygen to the roots. Oxygenation methods like air stones in hydroponics or well-aerated soil can prevent root rot and subsequent yellowing leaves.

Light and Temperature Control

• Light Spectrum: Be aware of light spectrum requirements during flowering. Cannabis plants benefit from a spectrum that includes red and blue wavelengths. Adjust your grow lights accordingly.
• Temperature Differential: Consider creating a slight temperature differential between day and night. This temperature drop can encourage resin production and reduce the risk of stress-related yellowing.

Pest and Disease Prevention

• Companion Plants: Experiment with companion planting by incorporating pest-repelling plants like marigolds or basil among your cannabis. This natural approach can deter common pests.
• Neem Oil: Neem oil is a natural and effective pesticide. Dilute it and apply it preventively to your plants, especially during the vegetative stage.
• Quarantine New Plants: If introducing new plants into your growing space, quarantine them for a period to ensure they are pest and disease-free before introducing them to your main crop.

Environmental Optimization

• CO2 Enrichment: Consider CO2 enrichment techniques if growing indoors. Elevated CO2 levels can boost plant growth and resilience, reducing stress-related issues. If you are not sure, check this post for help: When to Stop CO2 During Flowering
• Lighting Timing: Maintain a consistent light cycle during flowering. Any interruptions or irregularities in the light schedule can stress the plants and lead to leaf issues. For optimal lighting conditions, opt for an LED grow light for plants. 

Conclusion

Leaves turning yellow during flowering is a common challenge for cannabis growers. However, armed with knowledge and the right strategies, you can ensure your garden flourishes with vibrant blooms. Remember to address nutrient deficiencies, practice proper watering, and stay vigilant against pests and diseases. With these expert tips and solutions, your garden will be a testament to your green thumb.

FAQs about Leaves Turning Yellow During Flowering

1. Why do my plant’s leaves turn yellow during flowering?

Leaves turning yellow during flowering can result from nutrient deficiencies, watering problems, pests, or natural aging of the plant.

2. How can I determine if my plant lacks nutrients?

Perform a soil test to assess nutrient levels. Yellowing leaves, especially if accompanied by other symptoms like stunted growth, can indicate a deficiency.

3. Is it normal for some leaves to turn yellow?

Yes, it’s natural for older leaves to yellow and fall off as the plant allocates resources to new growth. However, widespread yellowing may indicate an issue.