CO₂ enrichment is a highly effective method for enhancing plant growth and maximizing yield, particularly in cannabis cultivation. By optimizing CO₂ levels at each stage of growth, growers can significantly improve plant size, potency, and quality. However, CO₂ enrichment is not a stand-alone solution, it must be integrated with proper lighting, temperature, humidity, and ventilation controls for maximum benefit.

Understanding the interplay between these environmental factors allows growers to create the perfect environment for cannabis cultivation. Elevated CO₂ levels combined with high-intensity lighting, temperature control, humidity management, and effective HVAC systems create an environment where plants can thrive.

When all of these systems work together in harmony, growers can achieve higher yields, better quality, and more efficient and repeatable operations, leading to greater profitability and success.

Lighting

• Photosynthetically Active Radiation (PAR): CO₂ enrichment is only effective if plants are exposed to sufficient light. Photosynthetically active radiation (PAR) refers to the spectrum of light that plants use for photosynthesis, which includes light from 400 to 700 nanometers. To maximize the benefits of CO₂, growers must ensure they provide high-intensity lighting with adequate PAR levels, typically using LED or HPS (high-pressure sodium) grow lights.
• PPFD stands for Photosynthetic Photon Flux Density, which refers to the amount of PAR falling in a given area per second.
• Lighting Duration: During the vegetative stage, cannabis plants require 18–24 hours of light per day. In the flowering stage, lighting should be reduced to 12 hours to encourage bud development. CO₂ enrichment can significantly enhance growth when paired with high light intensities, but light intensity must be balanced to prevent plant stress.

Temperature

• Optimal Temperature Range: Cannabis plants grow best in a temperature range of 70–85°F (21–29°C) during the vegetative stage and 65–80°F (18–27°C) during flowering. CO₂ enrichment allows plants to tolerate slightly higher temperatures because it accelerates their metabolic processes.
• Temperature and CO2: When CO₂ levels are elevated, the plant’s stomata tend to stay open longer, leading to increased transpiration. This allows the plant to tolerate higher temperatures, making CO₂ enrichment particularly useful in warmer environments. However, temperatures that are too high (above 90°F/32°C) can stress the plant and reduce its ability to photosynthesize effectively, even with CO₂ enrichment.

Humidity

• Ideal Humidity Levels: Humidity plays a significant role in CO₂ absorption and overall plant health. The ideal humidity levels for cannabis plants are:
  • Vegetative stage: 50–70% relative humidity (RH)
  • Flowering stage: 40–50% RH
• CO₂ and Humidity: Elevated CO₂ levels can increase transpiration rates, which affects humidity. Proper humidity control ensures that plants do not suffer from moisture stress, mold, or mildew, particularly during flowering when lower humidity is necessary to avoid bud rot.

Ventilation and HVAC Systems

• Air Circulation: Effective air circulation is essential to ensure even distribution of CO₂ throughout the grow space. Poor air circulation can lead to CO₂ pockets, where some plants receive too much CO₂ and others too little, resulting in uneven growth.
• CO₂ and HVAC Integration: Heating, ventilation, and air conditioning (HVAC) systems must be designed to work in harmony with CO₂ enrichment. HVAC systems should include CO₂ sensors and be capable of adjusting airflow to maintain ideal CO₂ levels, temperature, and humidity. Proper ventilation also helps prevent excess CO₂ buildup, which can pose risks to workers.
• Exhaust Systems: Growers must have exhaust systems in place to vent excess CO₂ and prevent levels from becoming dangerous. Automated systems that monitor CO₂ levels and adjust ventilation accordingly ensure that the growing environment remains safe and productive.

Stages of Cannabis Cultivation and Optimal CO₂ Levels

Cannabis, like other plants, responds strongly to controlled CO₂ enrichment. However, different stages of cannabis growth require different CO2 levels to maximize growth and quality.

1. Clone/Seedling Stage:

• CO₂ Levels: 400-500 ppm.
• Lighting: 200-400 PPFD (low light intensity)
  • Light Type: T5 fluorescents or low-power LEDs.
  • Duration: 18-24 hours light cycle.
• Water & Soil: Proper drainage, pH-balanced water (5.5-6.5), and seedling-specific nutrients.
• Ventilation: Light airflow to avoid over-drying, using small inline fans.

2. Vegetative Stage:

• CO₂ Levels: 800-1200 ppm.
• Lighting: 400-600 PPFD (medium intensity)
  • Light Type: Metal Halide (MH) or high-power LEDs.
  • Duration: 18-24 hours light cycle.
• Water/Nutrients: Nitrogen-rich nutrients with ample water; maintaining proper soil oxygenation.
• Ventilation: Inline and oscillating fans for air circulation, humidity control at 60-70%.

3. Flowering Stage:

• CO₂ Levels: 1200-1500 ppm.
• Lighting: 600-1000 PPFD (high intensity)
  • Light Type: High-Pressure Sodium (HPS) or high-power LEDs.
  • Duration: 12 hours light cycle.
• Watering: Adjust pH for nutrient absorption, ensure phosphorus and potassium-rich nutrients.
• Ventilation: Maintain humidity below 50%, with high air exchange using exhaust fans, carbon filters for odor, and CO₂ dosing systems.

4. Pre-Harvest Stage:

• CO₂ Levels: Taper down to 400-600 ppm.
• Lighting: Reduced light exposure for ripening.
  • Light Type: Same lights, but intensity reduced.
• Watering: Flush plants with pH-neutral water, no nutrients.
• Ventilation: Ensure optimal airflow, prevent mold buildup.