Using UV and Far Red Light in Cannabis Cultivation: How and When to Apply for Maximum Benefits
março 13 2025 – Danielle Daly
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?
UV light serves multiple functions in cannabis cultivation:
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Integrated Pest Management (IPM): UV light helps reduce powdery mildew (PM), fungus gnats, spider mites, and other pests.
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Enhanced Cannabinoid and Terpene Production: UV exposure triggers a stress response in plants, leading to increased THC, CBD, and terpene levels.
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Cleaner and Stronger Plants: UV 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:
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Avoid Yield Reduction: UV exposure can damage plant DNA, potentially reducing yield if applied too early. Using it only in the last 2-3 weeks allows plants to bulk up before stress is introduced.
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Trigger Protective Responses: During this period, controlled UV exposure activates stress-induced resin production, increasing oils, cannabinoids, and terpenes without negatively affecting yield.
2. IPM: At Night, BUT BE Careful to Prevent Photoperiod Disruption
Cannabis plants are sensitive to light schedules, and introducing UV during night hours can disrupt photoperiods, especially in flowering. The most effective approach is to apply UV at no more than 1 hour at night:
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Best Timing: Use UV 10 minutes to 30 minutes before lights turn on or 30 minutes immediately after lights turn off.
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Why? Research (including studies from Cornell University) shows PM defense mechanisms shut down at night, making UV more effective in eliminating it during this window.
How to Apply UV Safely and Effectively
1. Proper Intensity and Duration
UV intensity matters. Many manufacturers offer low-wattage solutions (10W-30W) that are too weak to make a real impact. To be effective, 100W-180W UV solutions are recommended.
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UVB (310nm): Enhances THC production while minimizing plant damage.
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UVA (400nm): Supports plant growth and resin development.
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Start Slow: Begin with short exposure times and gradually increase.
2. Pest and Disease Control with UV
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Powdery Mildew (PM): Use UV for 30 minutes immediately after lights out and again 30 minutes before lights on.
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Spider Mites & Thrips: UV needs direct exposure to kill pests, so ensure coverage across the canopy.
3. Safety Considerations
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Human Protection: UV light is harmful to skin and eyes. Always wear protective gear and avoid exposure.
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Environmental Control: Ensure UV use is timed properly and does not interfere with plant development.
The Role of Far Red Light in Cannabis Cultivation
What is Far Red Light?
Far Red light (700-750nm) 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
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Using Far Red continuously helps enhance plant growth, improves light absorption, and increases overall yield.
2. Morphology Control: Stretch vs. Compact Growth
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To Promote Stretch: Use Far Red with reduced intensity on other channels.
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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.
Strategic Use During Flowering Stretch
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First 5-15 Days of Flowering: If you need plants to stretch less, use Far Red strategically (low to off) in this early phase.
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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.
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