26/09/2022

UV light and cannabis plants

In this article we look at the importance of UV radiation in the cultivation of cannabis plants. What effect does this light have on plant development? and especially the production of cannabinoids and other compounds.

UV light and cannabis

It should be said at the outset that the vast majority of lighting for indoor growing does not emit any UV radiation. Unlike the sun, which is the biggest source of complex radiation.

From the grower’s point of view, the most important compounds in cannabis are undoubtedly cannabinoids such as THC and CBD, as well as terpenes, which give our favourite plants their characteristic aroma and taste. Now for the important news: exposure to short wavelengths such as UVA and blue light triggers stress reactions in the plant and it starts to protect itself. How does it do this? Increased stress levels result in increased production of secondary metabolites, and therefore higher accumulation of THC, other cannabinoids and terpenes.

Effect of spectrum on the structure of cannabis plants

Effect of UV light on the structure of cannabis plants
Structure of cannabis.

Plants read signals about their surroundings from temperature, light spectrum, soil moisture, etc. Irradiation with short wavelengths -UVA light gives the plant a signal that it is under clear skies and without the shade of neighbouring plants. This environment tells the plant that it does not need to rush to reproduce (flower production) or reach for light just yet. Plants grown under the rich blue and UVA spectrum usually have small leaf spacing, small leaf area and thick leaves. In short, they grow vigorously. This changes with the red spectrum, which stimulates stem elongation, increases leaf area and encourages cannabis to flower.

It is probably no surprise that in nature the strongest cannabis plants are usually found at high altitudes in mountainous areas. In such areas, the plants get plenty of bright sunlight, the spectrum of which has higher UV wavelengths than at lower altitudes. A higher proportion of the blue and UV spectrum is present during long summer days when the sun spends a lot of time high in the sky. The lower it is above the horizon, the more red spectrum there is (sunset, autumn and winter).

Pathogen protection

Protection of cannabis against pathogens.
Pathogen protection

As already mentioned, UVA radiation increases the production of metabolites ( THC or terpenes in the flowers ), but the grower can also benefit from the increased activity of secondary metabolites in other ways. A plant that is slightly stressed by UVA radiation also produces other metabolites – antioxidants and phenolic compounds – that protect it from stress down to the cellular level. These substances protect the plant not only from radiation but also from pathogens and pests. The result is a compact plant with an increased concentration of THC, which is also stronger against fungal pathogens. These include botrytis, a grey mould that destroys the ripening buds.

You can also read Symptoms and types of mould.

How to add a UV spectrum?

It is possible to add UV spectrum in a grow room using special bulbs, Adding a UVA or UVB bulb to a grow room is potentially dangerous as UV radiation is strong and can damage cannabis plants, your eyes and even the plastic it shines on. Excessive UV radiation can stunt a plant’s development and eventually kill it. That’s why it’s important to buy UV lights designed specifically for growing cannabis plants!

Tube with UV spectrum
Tube with UV spectrum
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Published by Jan Horák

26/09/2022
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