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is uv light good for growing weed

Is uv light good for growing weed


Finally, let’s touch on UV-C. This wavelength is mostly used in clean-lights and to purify air for indoor areas. It’s a great tool for cleaning and removing contaminants from a grow environment. It can be beneficial as a direct leaf application to control certain types of powdery mildew. It is important to note that the amount of tissue damage from UV-C on leaves and buds is not always worth the help, and long exposure to UV-C or UV-B has been shown to adversely affect plant tissue. It creates an almost burned look on buds and leaves an opening to a secondary invasion from pathogens.

D.T. Krizek, Influence of PAR and UV-A in determining plant sensitivity and photomorphogenic responses to UV-B radiation, Photochem. Photobiol. 79 (2004) 307–315.

Is UV Worthy of All The Hype?

M. Götz, et al., PAR modulation of the UV-dependent levels of flavonoid metabolites in Arabidopsis thaliana (L.) Heynh. leaf rosettes: cumulative effects after a whole vegetative growth period, Protoplasma 243 (2010) 95–103

Some studies are starting to look into the UV and Cannabis relation and show that UV-A (365nm) and UV-B in small doses or cycles are what really trigger photomorphogenesis within plants, especially cannabis. If these results are proven true, it would mean that UV should not be built-in to LED fixtures unless they have control over it through spectrum tuning or channel control. Interestingly, most LED fixtures on the market today that have UV built-in, have UV-A (395nm), which has yet to be shown any more effective than blue LEDs in the 400-450nm range. As a cautionary note, both UV-B and UV-C must be used with extreme caution around humans and it makes it virtually impossible to have either of these spectrums built-in to an everyday grow light.

The Dangerous Side of UV

As cannabis growers, many of us find this response alluring. On the surface, the concept of more purples and secondary compounds such as anythrocynine seem likely to lead to a better terpene and cannabinoid suite in our final product. The science, however, indicates that UV and Cannabis relation effects are minimal at best. Yes, we get more vibrant colors and possibly better trichome head production as well. Ironically though, it seems this can also be achieved with any full spectrum LED on the market without the extra stressor of UV light. As the scientific studies are lacking here, anecdotal stories and results are all that we can rely on today.

This begs the question, Why are so many cannabis growers certain that they need UV to achieve that ‘fire’ bud? The answer lies in a scientific exploration of UV light and how it influences plant morphology. All light consists of particles traveling in waves, and the distance between them, or the wavelength, determine the light’s properties. UV wavelengths cover a range of 100-400 nanometers (nm). UV-A light, at 315-400nm, has the longest wavelengths of the group. At 280-315nm, UV-B has shorter wavelengths and UV-C has the shortest at 100 – 280nm. In nature, plants encounter mostly UV-A and some UV-B. UV-C wavelengths, being so short, are mostly absorbed by the atmosphere and rarely make it to the ground.

Is uv light good for growing weed

Unfortunately, UV exposure is also connected with lower CBD levels. This is likely because there is a tradeoff between THC production and CBD production . To increase THC in the flowers of a cannabis plant, at least 1.34 Watt-seconds/m 2 of UV-B light is necessary. It should be given for 6 hours per day, for at least 40 days. Research shows that doing this increases Δ9-THC content from 2.5% to 3.2% [4] .

UV wavelengths can also help plants defend against insects. UV wavelengths, and to some extent, other wavelengths of light, can trigger plants to release defence compounds. Some examples of these defence compounds are volatiles (smells that deter insects), hormones (alert defence responses in other parts of the plant), secondary metabolites (change the colour and taste of a plant) and trichomes [5]. These compounds make a plant more distasteful or toxic to insects. As a result, plants with increased levels of these compounds get eaten less [6] !

UV Light May Decrease CBD Content

When UV light hits a leaf, the plant makes “sunscreen” to protect itself from damage [2]. Plants produce many different types of sunscreen. Some of these sunscreens are physical, like trichomes, and some of them are chemical, like anthocyanins and beta-carotene. Trichomes are hair-like growths found on the skin (epidermis) of plants. They protect the plant by reflecting away the harmful UV rays. In cannabis, these trichomes are the site of THC and CBD storage. For this reason, scientists wondered whether adding UV rays could increase THC content in cannabis plants.

Growers who want to increase the potency of their cannabis may consider adding ultraviolet (UV) light to their grow setup. UV light is radiation with wavelengths between 100 – 400 nm and it’s not visible to the human eye. Outdoors, about 10% of the sun’s light is ultraviolet. Furthermore, UV light is broken down into several subtypes, including UV-A (315 – 400 nm), UV-B (280 – 315 nm), and UV-C (100 – 280 nm). Most lighting technology provides little UV light. So, to match the intensity of the sun, you would need a light that produces at least 32 W of UV radiation [1] A quick Google search shows that it’s not easy (or cheap) to find a light that can deliver this much light! And so this may make growers wonder: Are these lights worth the price? And — do cannabis plants even need UV light?

UV Light May Not be the Most Effective Way to Increase Trichomes

Scientists surveyed cannabis strains that originated from different places around the world. They looked in places that had high UV levels (like near the equator, or on tall mountains) as well as places with low UV levels (away from the equator and in shady spots). They found that strains from the equator and high-altitude regions had more THC [3] .

Is uv light good for growing weed

Far-Red and Infrared Light

Exposure to UVB radiation is also known to reduce a plants biomass, plant height and leaf area, but increase leaf thickness, terpene and resin production. Cannabis cultivators who’s main goal is to boost the amount of fragrant enhancing terpenes and oils for edible, tincture or waxes, rather than focus on high yields may choose lighting such as Metal Halide that provides some level of UVB radiation or supplement their current lighting with UVB reptile lights.

UVB (280-315nm) has a short wavelength, high energy and also causes sunburn in humans and plants. UVB is known to damage protein and nucleic acids in plant cells, causing decreased metabolism and decreased number of flowers. UVB can have positive effects for plants as well. Cannabis responds to the stress and sunburn from UVB wavelengths, by creating it’s own sunscreen in the form of trichomes. The more trichome production the higher the THC, CBN and CBD levels.

/>ReptiSun Reptile Fluorescent T5H0 Lamp

Ultraviolet Light (UV)

Many of the spectrum wavelength ranges I mention above are visible to the human eye, but plants require wavelengths above and below the visual spectrum of light that includes ultraviolet (<400nm) and far-red/infrared (>700nm).

The appropriate amounts of far-red and infrared light can also be a very effective at promoting robust stem growth, proper node spacing, and more flowers and fruit. Too much IR radiation can also be an issue because to plant the majority of IR radiation is felt as heat. Growers who use traditional 1000W HPS lighting, which produces excess heat through IR radiation, have to install and operate expensive HVAC systems to mitigate the heat. Too much IR radiation can cause plants to stretch spreading out the plant nodes, can discolor the leaves or even kill the plants. Choosing a light with the right appropriate amount of far-red and infrared light is key for healthy and natural plant growth.

On the far end of the spectrum (>700nm) you find far-red and infrared wavelengths of light. Far-red and infrared light have very long wavelengths, and very little energy. Infrared wavelengths are not visible to the human eye and only can be felt as heat. We know that blue and red light is optimal for plant development, but research conducted in 1957 has shown that combining blue light and red light with far-red/infrared light (700-760nm), led to an increased rate of photosynthesis due to the Emerson effect. The protein Phytochrome is the only known receptor that is sensitive to far-red/infrared wavelengths. Plants use Phytrochrome to regulate when a plants is to switch from vegetation state to flowering, and the time of flowering, due to the length of daylight or exposure to artificial light.

Finally, UVA and near ultraviolet light (315-400nm) has the longest wavelengths of UV light and can be very beneficial to plant development. UVA has also been shown to increase the amounts of THC, CBD, and terpene production in cannabis plants, without the negative effects of UVB. Wavelengths in the UVA spectral range are included in the absorption spectrum, particularly in the 380nm range. The absorption spectrum is the range of wavelengths of light that are absorbed by green chlorophyll for photosynthesis. Additionally, research has shown that exposing plants to UVA light can also inhibit mold growth and fungal development.