As medical cannabis or medical marijuana becomes legalized in more regions around the world, this represents an exciting new market for growers. But how do you get the best results when growing this crop in a greenhouse under LED lighting? Signify Plant Specialist Sabrina Carvalho has carried out several trials with research partners. In this blog, she answers the question based on research in collaboration with Wageningen University & Research: Can you increase yields for medical cannabis with LED lighting?

There were several significant results from the trials I carried out over a number of months. First, the results show that if you grow medical marijuana crops in a greenhouse under LED lighting it’s possible to achieve higher yields and faster growth cycles for the plants. Second, the results show that growing medical cannabis in a greenhouse optimized for LED grow lights enables you to shorten the overall growth phases considerably as well. But how?

Achieve up to 1 more cycle per year with LED

As shown above, results from the trials show that the vegetative phase, for example, can be shortened by 5 days to a total of 9 days with LED lighting, because during this phase the most intense and vigorous growth occurs. The flowering phase was shown to be even 13 days shorter with LED lighting compared to HPS (high pressure sodium) lighting. This means that with LED grow lights you can complete the total crop cycle in just 72 days, compared to 85 days with HPS lighting, allowing you to harvest an average of one more crop per year with LED lighting. Besides being able to harvest an extra crop per year, the trials show that crops grown under LED lighting also produced a 40% higher yield*.

A shorter growth cycle, yet 40% higher yield with LED

It is important to mention that it’s crucial to adapt the climate of the greenhouse specifically for LED grow lights and to steer the climate in a different way, meaning that you will have to make some adjustments compared to growing with HPS lighting. With HPS for example, you can’t reach the same light intensity as with LED without causing temperature problems. With LED you get much more PAR (Photosynthetically Active Radiation) light for the same amount of energy compared to HPS. LED lighting also produces much less radiant heat, so your temperature set-point could be several degrees Celsius higher, for example. All in all, when growing medical marijuana with LED you must steer the climate in a different way. It really is a different way of growing.

The trials compared results of medical cannabis crops grown under HPS and LED lighting in a greenhouse. First, a crop was grown under HPS lighting. After this crop was harvested, another crop was grown under LED lighting under the same conditions and in the same trial area. This set-up was repeated several times under HPS and the LED set-up was run a total of 3 times in that same compartment. Afterwards, the two cycles and crops were compared.

In our long-term research collaboration with Wageningen University & Research (WUR), we are investigating how LED grow lights can influence compound production, quality and plant characteristics of cannabis crops grown for medical purposes. The research results will support growers in creating the ideal growing conditions for medical cannabis. Read more about the scope of the research in our press release and follow the Horti blogs from Signify to read results as they become available.

*These results are based on the specific characteristics of these trials. We can estimate yields of 50-100 grams per plant, depending on the variety, planted at a density of 9-10 plants per square meter. The LED light intensity used was a medium intensity of 800 µmols/m2/s.