I read forums that are full of posts about how UV is either great or useless, but little real info, only anecdotal info. I understand this lack of real and wanted to clear up a few things. I’ve never grown cannabis, but I’ve worked with hundreds of growers and have a pretty good grip on the science behind it, so our company experiences is based on more than anecdotes. Many of these growers have tested in controlled experiments and use testing labs to measure the output. All this verifies what the basic science says, that UV light WILL increase THC, if used properly.
First, you have to understand the basic science behind it. What we are doing is exposing the flower or bud to UV light during the flowering state. Exposing the leaves themselves isn’t as helpful, although it might help trigger a defense response as well. From the plant’s perspective, the flowers/buds are its children, where the seeds will be. Granted, the plant doesn’t know you aren’t going to let the flowers be fertilized and go to seed, but it is still the nursery for the plant, the only way it has to spread its DNA for another year. It naturally wants to defend this seed pod of sorts. Plants and animals have devised methods of protecting their young for millennia, the cannabis plant is no different than any other, except in how it protects its “young”.
Ultraviolet is a damaging set of wavelengths, literally a color just beyond violet in the rainbow, hence the name “ultra-violet”, or “just beyond violet”. A little UV is good for us, helps us create vitamin D and such, but too much causes sunburn and can actually damage DNA. This is how you get skin cancer, by getting way too much UV. There are similarities with plants in that they are used to UV, perhaps even requiring it for optimal growth and certainly for maximum THC. Cannabis evolved outdoors where there is a lot of UV. Indica strains have been exposed to particularly high levels of UV over the tens of thousands of years the plant has been evolving, because they are native to higher elevations where the UV level reaching the ground is higher. The indica genes have a higher tolerance for UV because of this, and most indoor growers use indica hybrids, so they likely have these same genes.
This begs the question: how did cannabis plants learn to cope so many years ago? The answer is THC. Forget that THC is a psychoactive drug for a bit, and lets examine the biological role in the plant. THC isn’t found in any appreciable amounts in the sun leaves or stems, the part of the plant that is somewhat disposable if you are trying to spread your genes. It is found only on the flowers and to a lesser degree, the “sugar leaves” around the flower. There is a reason for this. The plant evolved THC as a covering for the flowers because it is a chemical that has a very high absorption ability when it comes to UVA/UVB. It is literally a sunscreen, blocking out the ultraviolet and keeping it from reaching the flower and seeds. How it got there is simply Darwinism. That it has psychoactive properties is perhaps coincidence, as the plant didn’t evolve simply to please humans.
During the plant’s evolution, plants that developed THC had a better chance of surviving, of having more seeds, and out-competed plants that didn’t, and over thousands of years, only the plants with THC were left. Then, plants with high THC were more likely to survive compared to plants with low THC, and a race for higher THC was started, probably before the first human even noticed the plant. Obviously there are other factors, other genes that determined which plants were most likely to survive, but unquestionably, THC played a role in the success of the survivors. Nature has literally designed the plant to function in a high UVB environment by giving plants an advantage if they could produce lots of THC. It is a bit ironic that it took the first mutation that created THC in the plants to begin with, to create a chemical that would prevent mutations. Whether it was caused by cosmic rays, ultraviolet or just random mutations, we will never know. What we do know is that cannabis can tolerate an amazing amount of UV by covering its flowers with THC.
Now we look at modern times, where man (and the law) has pushed horticulture into basements and warehouses, under artificial light, in sterile and contrived environments where we try to recreate the best parts of nature. We use the best seeds only, custom hybrids designed for the highest THC, and put them in perfect little plant heavens, free from the stresses of outdoor living. For the most part, we get pretty good results, but something is missing: Stress.
Just as it takes a little breeze to make the stems grow bigger and stronger, it takes UV to make the buds develop more trichomes and maximum THC. If you don’t put a stress on them, they have no reason other than to produce a “standard amount” of THC. If you push them hard, they react by taking energy that would be used for leaves and such, and instead convert that energy into THC. You have put them in protect mode, and higher THC is your reward.
This is’t magic, or voodoo, or trickery, it is basic biology. If you expose a human to UV over time, they protect themselves with a tan. If you do it to a tomato, it will thicken up the flesh and produce flavanoids as a response. If you do this to cannabis, it will protect the buds by producing as much THC as it needs to protect its “seeds”. The key is to simply give the buds as much UV as they can handle, in the right frequencies (single phosphor or LED just doesn’t work here, and UVC will wipe out your crop) and watch the results. Each strain is different, so it takes some tweaking, but the principle is the same: run the UV lights every time your regular lights are on, and run them as close to the buds as you can, and rotate to make sure every bud gets some UV.
Any source of UVB is better than nothing, but the Universal UV and SG-1 series work best and are actually cheaper because of how much UV they produce, several times more than reptile lights. Regardless of what else you do, adding UV will push your plants into maximum protection mode, maximum THC mode because we are “plant hacking”, ie: using the plant’s own system to force it into producing more THC, the same way mother nature does.