Understanding the Last Two Weeks of Cannabis Flowering: Fertilization and Watering Strategies

Cannabis growers often question the best practices for the final stages of their plants' life, especially when it comes to watering and nutrient management. This article aims to clarify these often debated topics, providing insights based on scientific research and practical experience.

Introduction to the Final Weeks of Cannabis Growth

The last few weeks of a cannabis plant's flowering phase are critical in determining the plant's final yield and quality. During this stage, growers may consider flushing their plants, which involves the cessation of fertilization and leaching of nutrients from the growing medium. This practice is often accompanied by questions about the necessity of using pure water for the last two weeks of a plant's life.

Flushing: A Controversial Practice

The concept of flushing is widely recognized in the cannabis industry, but its effectiveness is often debated. Flushing is the process of watering plants with plain water instead of nutrient-rich solutions during the final weeks of flowering. The theory behind flushing is that it may lead to improved smoke quality by reducing nutrient levels in the buds. However, this idea lacks scientific backing.

Scientific Evidence on Flushing

A study conducted by the University of Guelph found that flushing for as little as two weeks before harvest had no significant impact on the elemental or cannabinoid concentration of dried flower buds. This indicates that flushing does not remove nutrients from the bud, contrary to popular belief.

Impact of Flushing on Yield and Quality

While flushing may not remove essential nutrients, it can have detrimental effects on yield and quality. Research has shown that increasing the duration of flushing can lead to a decrease in dried bud weight. For instance, a study found that as flushing duration increased from 2 weeks to 4 weeks, the dried bud weight decreased by 8-12%. Additionally, sulfur concentration increased in buds flushed for 1 week or more, which can result in off-flavors and odors.

Optimizing Cannabis Growth with Proper Fertilization

A new school of thought in cannabis cultivation suggests that properly fertilized plants may not require flushing. This perspective is based on the idea that plants that are well-nourished throughout their growth cycle may not need to purge stored nutrients.

Monitoring Nutrient Levels

Proper nutrient management involves closely monitoring the concentration of nutrients in the system (PPM levels). By adjusting nutrient strength based on daily readings and the plant's needs, growers can ensure optimal growth and yield. As the plant approaches its final weeks, nutrient levels may naturally increase, signaling that the plant is ready to focus on producing buds rather than foliage.

Watering Strategies

For hydroponic growers, avoiding water-only irrigation in the final weeks is advisable, as the plant needs the essential nutrients to achieve its best potential during this critical period. Throughout the flowering phase, it is recommended to use nutrient solutions rather than just plain water to support plant health and maximize yield.

Best Practices for Watering and Fertilization

To ensure optimal nutrient levels and avoid fluctuations, growers should:

Monitor PPMs regularly and adjust nutrient strength accordingly. Use a closed-loop system to prevent nutrient loss. Flush with water-molasses solutions in the last few weeks if nutrients were overdone. Check and adjust pH levels during every irrigation cycle. Use calcium-magnesium supplements for well water or RO-filtered water to maintain stable pH levels.

Conclusion

The last two weeks of a cannabis plant's flowering phase are crucial for maximizing yield and quality. While flushing may not be necessary for properly fertilized plants, regular monitoring of nutrient levels and using the appropriate watering strategies is essential. By following these best practices, growers can produce healthier, more flavorful buds for improved overall quality.