Using UV and Far Red Light in Cannabis Cultivation: How and When to Apply for Maximum Benefits

Harnessing UV and Far Red Light in Cannabis Cultivation: Optimizing Quality, Yield, and Plant Health

Ultraviolet (UV) and Far Red light have become powerful tools in cannabis cultivation, offering benefits for pest management, disease prevention, cannabinoid enhancement, and plant morphology. However, improper use can damage plant DNA, reduce yields, or impact plant structure. To harness their full potential while minimizing risks, it’s essential to apply UV and Far Red at the right time and with the right dosage.

Why Use UV on Cannabis Plants?

Integrated Pest Management (IPM):
UV light helps reduce powdery mildew (PM), fungus gnats, spider mites, and other pests. Research indicates that UV exposure can enhance plant resistance mechanisms, effectively disrupting pest and disease cycles. For instance, a study by Robson et al. (2019) demonstrated UV’s ability to improve plant defense responses against common pathogens.

Enhanced Cannabinoid and Terpene Production:
UV exposure triggers a stress response in plants, leading to increased THC, CBD, and terpene levels. However, findings are mixed. A study by Rodriguez-Morrison et al. (2021) observed minimal changes in cannabinoid and terpene output from UVB exposure alone, highlighting the importance of specific wavelength, dosage, and timing. Conversely, research by Huebner et al. (2024) found that UV treatment significantly boosted terpene levels like linalool, limonene, and myrcene—contributing to richer aroma and therapeutic potential—without disrupting cannabinoid balance.

Cleaner and Stronger Plants:
UV light can help reduce microbial contamination, supporting healthier plant growth and passing strict microbial testing standards. 

When to Use UV Light on Cannabis Plants

1. Quality: During the Last 2–3 Weeks of Flowering
The best time to introduce UV light is at the end of the flowering cycle. Here's why:

• Avoid Yield Reduction:
  Early UV exposure can damage plant DNA and reduce biomass. Applying UV only during the last few weeks allows plants to bulk up fully before introducing stress. Use UV for the full 12/12 cycle at up to 100% strength—but ramp up slowly while monitoring plant response.

• Trigger Protective Resin Responses:
  Controlled late-stage UV exposure activates the plant’s natural defense mechanisms, stimulating increased resin production and boosting oil, cannabinoid, and terpene levels without harming yield.

2. IPM: Apply UV at Night—Carefully
Cannabis plants are sensitive to light schedules, so applying UV at night must be done cautiously to avoid photoperiod disruption.

• Best Timing:
  Use UV for 10–30 minutes before lights turn on, and/or 30 minutes immediately after lights turn off. Studies, including work from Cornell University, indicate that PM defense mechanisms shut down at night—making UV more effective during these transitional periods.

How to Apply UV Safely and Effectively

1. Proper Intensity and Duration
Many low-wattage UV solutions (10W–30W) are too weak for meaningful results. For impactful use, high-output solutions like Mammoth’s 100W–180W UV systems are recommended.

• UVB (around 310 nm): Boosts THC production with minimal plant stress.

• UVA (around 400 nm): Enhances growth and supports resin development through PAR/blue spectrum overlap.

Always start with low exposure durations and build up gradually.

2. Pest and Disease Control with UV

• Powdery Mildew (PM): Apply UV 30 minutes after lights go off and again 30 minutes before lights come on to target vulnerable pathogen windows.

• Spider Mites & Thrips: Ensure UV light reaches all parts of the canopy—direct exposure is key for effectiveness.

3. Safety Considerations

• Human Protection: UV light is harmful to eyes and skin. Wear proper protection and avoid direct exposure.

• Environmental Control: Use UV on timers to avoid disrupting the light cycle and plant development.

The Role of Far Red Light in Cannabis Cultivation

What is Far Red Light?
Far Red light (700–750 nm) is a spectrum just beyond visible red light. It influences plant morphology by affecting stretch, canopy structure, and flowering.

The Emerson Effect: Far Red’s Role in Enhancing Growth
The Emerson Effect occurs when Far Red light is combined with other light wavelengths (like red and blue), increasing photosynthesis efficiency. This allows plants to use energy more effectively, leading to faster growth and higher yields.

How and When to Use Far Red Light

1. Full-Time Use for Increased Growth Efficiency
Using Far Red continuously helps enhance plant growth, improves light absorption, and increases overall yield.

2. Morphology Control: Stretch vs. Compact Growth

• To Promote Stretch: Use Far Red with reduced intensity on other channels.

• To Keep Plants Compact: Turn off the Far Red channel or reduce its intensity. This limits excessive elongation, creating a shorter, more robust plant structure.

3. Strategic Use During Flowering Stretch

• First 5–15 Days of Flowering: If you need plants to stretch less, use Far Red strategically (low to off) in this early phase.

• After Stretching Phase: Once desired height is achieved, increasing Far Red can help maintain plant structure.

The Future of UV and Far Red in Cannabis Cultivation

UV and Far Red technology are revolutionizing indoor and greenhouse cannabis farming. While they’re not silver bullets, they are powerful tools when integrated correctly. Combining UV and Far Red with proper environmental controls, high-quality grow lights, and strategic management plans will result in higher yields, better quality, and healthier plants.

For growers looking to test UV and Far Red technology, we offer high-power, precision-engineered solutions designed specifically for cannabis cultivation.

Got Mammoth? Patented + Engineered in Upstate NY... Inspired by Nature, Perfected by Science.

Further Reading & Research

• Cornell University Study on UV & Powdery Mildew – Read More

• Huebner et al. (2024) – UV Boosts Terpene Profiles in Cannabis

• Rodriguez-Morrison et al. (2021) – UVB and Cannabinoid Response in Cannabis

• Study: UV Light Intensity and Spectrum Influence Cannabis Growth and Terpene Profiles – Read More

• The Impact of Light Quality on Cannabinoid and Terpene Production – Read More