‘Far red light boosts root formation’. Wannida Sae-Tang Of course, we all knew this long ago: cannabis plants need a lot of light. Growers often walk into the problem of a massive electricity usage. But now the link between light and yields has been demonstrated scientifically, as Wannida Sae-Tang (from Thailand) shows in her PhD thesis ‘Shining the spotlight on medicinal cannabis’.
In her doctoral thesis, Sae-Tang examines the cultivation of medicinal cannabis, but the results are equally relevant for home growers of cannabis. In fact, the thesis reads as a manual for growers of all kinds. She mainly focuses on the effect light has on the plant in the various stages of development, from the formation of roots through to flowering.
Never grown cannabis
Sae-Tang had never grown a cannabis plant before she came to Wageningen. ‘I wanted to do research on the growth of medicinal plants in a controlled environment,’ she explains. ‘My supervisor Leo Marcelis asked whether I would be interested in a project on cannabis that was just starting. Thailand was also working on the legalization of medicinal cannabis around that time, so it was a good fit.’
Sae-Tang learned about the cultivation from professional growers working for the German medicinal cannabis company Aphria, which is co-financing the cannabis project along with the Dutch lighting company Signify. Her start was not easy. Three months after Sae-Tang came to Wageningen, the Covid pandemic broke out in the Netherlands. So the cultivation lessons were online to begin with.
Ideal plant
Sae-Tang’s experiments made one thing clear as daylight: the cannabis plant likes light. The plant can cope with at least three times as much light as other plants. That makes it an ideal plant for studying photosynthetic capacity. That extra light has a beneficial effect too. One per cent more light in the flowering stage leads to one per cent more flowers and an equal increase in the useful substances that can be extracted.
According to Sae-Tang, that doesn’t mean you can expose the flowering plants to unlimited amounts of light. ‘I assume there is a limit, even if we didn’t reach that saturation point with our lighting. But I also think the light isn’t the main limiting factor in the end. If you apply more light, other variables need to change too. More CO₂ is needed, the plants need enough water and the temperature has to be right. That requires careful monitoring and alignment.’
If you apply more light, other variables need to change too
Wannida Sae-Tang, Horticulture and Product Physiology
In addition to the amount of light, Sae-Tang also studied the effects of the colour of the light. She found the colour doesn’t matter much when the plant is flowering. That is good news for growers. ‘It means you don’t need any special lighting treatment and so you can make do with cheaper lights. But more research is needed on this topic.’
Far red
However, colour does have an effect during root formation. ‘Cannabis plants are propagated by taking cuttings,’ explains Sae-Tang. ‘Root formation is usually encouraged by dipping the cutting in a solution containing the growth hormone auxin. I discovered that far red light (just beyond visible red light, RK) boosts root formation. The use of auxin for medicinal cannabis is not permitted everywhere, so far red light could be a good alternative.’
