Cannabis Science

11 May 2021

How UVB Increases THC in Cannabis

The most potent cannabis in nature grows in high altitude mountain peaks and low latitudes near the equator. Interestingly, these two environments experience some of the highest levels of ultraviolet rays on earth. As a result, anyone growing marijuana outdoors in either one of these landscapes can expect overwhelmingly powerful plants rich in THC.

Scientific research into this phenomenon unveils a distinct correlation between ultraviolet rays, particularly UVB light, and increased THC production within cannabis plants. In addition, studies determined the stress from exposure to ultraviolet rays stimulates a plant’s defence system.

Furthermore, findings reveal that the plant’s natural reaction to the intense UVB rays directly affects the synthesis of cannabinoid and terpenoid compounds found in cannabis trichomes. Ultraviolet rays are radiation, and the fierce rays can be harmful to both humans and plants.

With this knowledge, though, marijuana growers can learn to manipulate UVB frequencies in a grow room under grow lights to increase THC content and cannabinoid production in cannabis plants.

What is Ultraviolet Radiation?

Ultraviolet radiation is electromagnetic energy that naturally comes from the sun. The light emitted from the ultraviolet spectrum isn’t visible to the naked eye; however, these rays are powerful. Human-made products such as mercury bulbs, tanning beds, and welding torches utilize ultraviolet energy in their applications. There are three different types of UV frequencies, categorized by their wavelengths.

UVA appears just below the visible light spectrum between 320 – 400 nanometers (nm). Their low energy, long wavelengths are 95% of the ultraviolet rays that reach the earth’s surface. UVA rays quickly sunburn human skin and can cause some skin cancers, especially when sunscreen isn’t used. In plants, UVA radiation sends photosynthesis into overdrive on a hot summer day.

On the other end of the UV spectrum, high energy, short-wavelength UVC rays don’t reach the earth’s surface as the ozone filters them out. These potent ultraviolet frequencies range between 100 – 290nm and are extremely dangerous. UVC frequencies are commonly used in sterilization processes.

The wavelengths that have the greatest influence on cannabis plant development are UVB rays. These intense rays fall between 290 – 320nm, but studies have shown that lower frequencies between 280 – 290nm make marijuana plants react more vigorously. This reaction occurs because UVB light rays ignite a plant’s defence system to kick in.

One of marijuana’s greatest attributes is the sticky, resinous coating of trichomes covering the plant in the flowering stage. Inside the mushroom-shaped structures is where the synthesis of valuable cannabinoids and terpenoids occurs. These magical structures are also a defence mechanism when the cannabis plant becomes stressed.

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How UVB Affects Cannabis Plants

Photomorphogenesis is the reaction from a plant exposed to particular light spectrums. Under strong UVB light, some plants wilt and die while others, such as cannabis, have a backup system for this stressful situation.

All systems are activated to begin trichome production as a means to thwart the sudden attack. The warning signal stimulates cellular activity to promote chemical synthesis, ultimately creating more cannabinoids to fill the newly manufactured defence trichomes.

Interestingly, cannabis plants have built-in protection from UV rays. A dimer protein, UVR8, is naturally activated to protect them from harmful UV rays. At this stage, the chemistry begins, and other enzymatic activity ultimately synthesizes acidic chemical compounds into active cannabinoid and terpene forms.

While the process is quite complex, cellular activity changes chemical compounds when the plant is stressed to bring out the best in a fine cannabis cultivar. Ionic charges, enzyme activation, and unique pathways transform the processes of cannabinoid and terpene manifestation. It is easy to visualize the chemical conversions as glandular trichomes change colours from clear to cloudy.

UVB increasing THC levels in marijuana plant

When to Apply UVB to Marijuana Plants to Increase THC

Outdoor cannabis plants naturally receive ample UV rays throughout their lifecycle. While most ultraviolet light coming from the sun is from the longer UVA wavelengths, roughly 5% comes from the UVB spectrum. Frequently, plants grown in outdoor gardens produce highly intoxicating THC -rich flowers.

Indoor growers can mimic the sun’s contribution by using ultraviolet light to increase cannabinoid and terpene production. However, it is generally recommended to only apply UVB light towards the end of the flowering stage and then just for short periods during the day. This added stress from the intense light in the last few weeks of flowering time accelerates the chemical processes of THC conversion.

Typically, applying UVB radiation to plants in early life stages is not advised as young, tender vegetative growth can burn quickly under ultraviolet light. Another critical time is when the marijuana plant begins reproduction in the pre-flower stage. Any added stress at this junction can cause the plant to hermaphrodite.

However, some old-school growers have a different take on UVB supplementation. Experimenting with reptile lights in underground indoor grow set-ups, marijuana growers found that low doses of UVB light during late veg and early flowering time helped toughen up the plant.

Some even ran lizard lights from the start when popping cannabis seeds, boasting the added UV light initiated germination. Most agree, however, that bumping the exposure time up each day towards the end of the plant’s life ensures a highly intoxicating experience from elevated THC levels.

Adding UVB Light in a Grow Room

Today’s indoor marijuana growers have many lighting options to choose from for their grow room. Metal halide and high-pressure sodium (HPS) bulbs have been the industry standard in cannabis cultivation for decades. High-intensity discharge (HID) bulbs, made with mercury vapours, emit ultraviolet rays. However, most of the UVB radiation cannot escape bulbs encased in glass.

When LED lighting manufactures began focusing on the cannabis industry, a few companies started incorporating UV rays into their schematics. Realizing the advantages of stressing marijuana plants to achieve increased beneficial effects, some lighting companies integrate UV diodes within their panels.

Currently, the drawback to LED grow lights is their hefty price tag. However, an economical option for cannabis growers to experiment with UVB light supplementation is with good old reptile lights.

Pros and Cons of Using UVB on Marijuana Plants

Since cannabis plants produce more trichomes under stress from UVB light sources, flavonoids, essential oils, and resin production also surge. Additionally, terpenes responsible for the great smells and flavours of a favourite strain multiply prolifically. But most importantly, the best attribute is the added influx of THC-infused trichomes.

Another positive feature of incorporating UVB lighting into a grow room is the intensity of the rays. Many pests, pathogens, and fungal spores cannot survive ultraviolet rays. Ultraviolet radiation quickly eradicates powdery mildew, botrytis, and pathogenic bacteria.

On the downside, the UVB spectrum is powerful and can easily lead to leaf bleaching when exposed to intense rays for too long. In this case, if leaf burning is too severe, marijuana plants cannot perform photosynthesis, transpiration, and other essential duties adequately.

Even worse, UVB can penetrate and damage genome DNA resulting in poor plant development. Sturdy cannabis genetics can withstand many stressful situations; however, frying any plant with too much ultraviolet radiation is not good.

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Post author
Charle Thibodeau
Charle’ Thibodeau is a freelance writer with almost a decade´s experience, specializing in cannabis content for the past two years. A strong motivation to educate, inform, and promote the culture surrounding this miraculous plant is her earnest mission.
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