Growing cannabis in a greenhouse is fairly new. Many growers build on their experience from either indoor facilities, or from growing other crops in a greenhouse. When growers started using artificial lighting, HPS fixtures were the common technology. Up until today HPS lamps are most commonly used in greenhouses. LED technology is in many ways a proven step forward. In comparison to HPS lamps, LED lighting has many advantages:
- Energy consumption
- Longer life span
- Heat radiation
- Used spectrum (wavelength)
What are the effects on the growth, development and relevant substance of medical cannabis in a greenhouse when you compare LED-lighting, measured at different light levels, with HPS-lighting?
In a 144 m2glass greenhouse growth area at Wageningen UR, 3 equal set-ups have been used to compare 3 dif ferent lighting regimes:
- 100% HPS at 250 μmol•s-1•m-2
- 100% LED at 250 μmol•s-1•m-2
- 100% LED at 400 μmol•s-1•m-2
The test has been executed during late spring (testing period from 06.04.2016 – 21.06.2016), therefore ‘autumn’ conditions have been artificially created with screens (LS 16 and blinds) to allow maximum 100 micromol sunlight to enter the greenhouse.
Two different varieties (cultivars) of cannabis have been tested. Both plants were THC (tetrahydrocannabinol) dominant varieties, but also CBD (cannabidiol) has been measured. In order to optimally test the influence of the different lighting recipes and levels, all other conditions like temperature, irrigation, humidity and nutrition were set equally.
Cannabis can grow perfectly under LED lighting. Compared with HPS the THC levels in plants grown under the Oreon Grow Light have been significantly higher. In 5 out of 6 treatments, the total weight (g) of THC and CBD were also highest under LED’s. In one treatment, that felt behind in total weight of THC and CBD, it was obvious that the plants grew too vegetative. The total fresh weight of the leave mass in that treatment was much higher compared to any other treatment. This evidently has been at the cost of the production of flowers. This treatment should have a more generative steering and the expectation is that the total weight of THC and CBD will be higher then as well.