Key Considerations For Indoor Cannabis Cultivation

LED Lighting: Plant-specific Spectral Composition

LEDs have an inherent advantage as a light source for plant cultivaiton solutions, since its color and spectrum could be customizable. LED grow lights are designed for different horticultural applications to provide proper light intensity, spectrum, and uniformity to increase plant yield and quality in Controlled Environmental Agriculture.

Different plants favor different types of spectrum of light for photosynthesis as well as different amount of PPFD.

When discussing lighting requirements for photosynthesis, we use horticulture lighting terminologies such as PAR, PPF, PPFD, and DLI.

✅ PAR:  Photosynthetically Active Radiation

✅ PPF: Photosynthetic Photon Flux (unit: μmol/s)

✅ PPFD: Photosynthetic Photon Flux Density (unit: μmol/m2/s)

✅ DLI: Daily Light Integral (unit: mol/m2/d)

Temperature: DIF Consideration

As the second most critical environmental factor influencing indoor plant growth, it must be understood that it is leaf temperature but not air temperature that controls the developmental rate of plants. Air temperature influences leaf temperature, but leaf temperature fluctuates more than air temperature because plants cool off by transpiration and warm up through irradiance.

For cannabis plants, the recommended growing temperature range is between 20°C (68°F) and 30°C (86°F). The night temperature should be lower than day temperature for a positive day/night temperature (+DIF) to promote stem elongation.

Temperature and light interact through photosynthesis. Therefore, testing for the best combination of light intensity and temperature for maximum photosynthesis is the key to optimize your cannabis growth and development.

CO2: Supplementing CO2 In Proper Way

In photosynthesis, while light is providing energy to drive this process, CO2 and water are digested by plants and

converted into assimilates (sugars) and oxygen. Assimilates and oxygen can then be converted back to CO2 and

water via respiration to release more energy to support the other biochemical processes needed for growth and

maintenance in plants. The surplus assimilates can be translocated to flowers.

CO2 is one of the limiting factors for photosynthesis. According to scientific data reported by Chandra et al. (2008), the photosynthetic rate of Cannabis sativa decreased 50% when CO2 levels dropped from 350 ppm to 250 ppm and increased 50% when CO2 levels increased from 350 ppm to 750 ppm.

Ralative Humidity: VPD Has To Be Monitored

Plant transpiration generally increases as humidity in the air decreases at the same temperature. Relative humidity (RH) measures the amount of water in the air at a given temperature, expressed as a percentage.

Air saturated with moisture has RH at 100%. RH is a very important factor but is easily overlooked. The lower the RH, the more water is evaporated from a leaf through transpiration. For example, at the same temperature of 21°C (70°F) a leaf loses more water at 10% RH than a leaf at 50% RH. Higher temperature causes more water loss from a leaf. At the same RH of 50%, a plant grown in 90°F loses more water than the one grown in 21°C (70°F).

A good indicator to monitor plant transpiration is called Vapor Pressure Deficit (VPD). During cannabis rooting or seedling stage, VPD is suggested to be lower to reduce transpiration for a better/fast establishment.