Will medical cannabis flower with LED lighting?

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 Almeida de Carvalho is carrying out several trials with research partners. In this blog, she answers the question based on research in collaboration with Wageningen University & Research: Will medical cannabis flower with LED lighting?

The simple answer to the question above is: ‘Yes, medical cannabis will flower when grown with LED lighting’. How much and how fast is a bit more complex. Medical cannabis plants are triggered to flower according to their photoperiod, which simply means the number of hours of light they receive. In general terms, plants like medical cannabis need to be in full darkness for at least 12 hours and sometimes longer, every day.

For plants like chrysanthemums and medical cannabis, we even talk about the ‘critical night’. They must go through a dark cycle to guarantee flowering. We’ve known this about medical marijuana since the 1910’s, thanks to studies carried out by Julien Tournois1 and B. Thomas2 on the light-darkness effect with hop and cannabis plants. In the 1970’s, Salisbury and Roos3 also documented their results with growing cannabis plants. It doesn’t matter what kind of light – sunlight, high pressure sodium (HPS) or LED lighting – the medical marijuana plant receives during the day, where the plant is in the growth cycle or, what light intensity medical marijuana plants are exposed to during the daytime, they will flower if they receive at least 12 hours of full darkness.

Flowering occurs with both HPS and LED, if the plants get at least 12 hours of full darkness