Using UVB for growing better cannabis is pretty much accepted universally now. There is simply too much science and anecdotes to ignore it. The big question isn't "should I use UVB for cannabis?" it is "how do I best use UVB for growing cannabis?". We have a variety of lamps because there isn't a single answer, although "stressing" is what we recommend. We will discuss it below:
First, you need to understand that ANY UVB is better than none. Even a reptile bulb or tanning lamp is better than using no UVB, although they aren't cheap to implement or maintain, and the results might be "better" but they are far from optimal. Still, they ARE better than nothing. What we are going to cover here, however, is more centered around the lamps we offer and the methods that our customers are swearing by. All the lamps discussed are capable of producing at least some 280-290nm, thus triggering the UVR8 protein. Virtually all non-Solacure lamps don't do this. It has to do with the patented glass we use.
Modes of operation
Low level continuous UVB. This means running a low to moderate UVB lamp for 12 hours a day during flowering. Assuming we are talking about a pure UV bulb like our SG-1-40, there are several things you can expect, including moderate gains in THC (10%-15% or more), and medium protection against mildew, mold and insects. This is probably the safest way to go because you don't have to worry about dialing in the right time or burning the plants. Our Universal UV and SG-1 series lamps are good examples of bulbs that people use for this, although the Universal won't trigger UVR8 like the SG-1 will.
High level pulse mode. This is used by a significant minority of growers for a couple of reasons. This will get an average of 15-25% increases in THC, moderate protection against insects but lower protection from powdery mildew and mold. The big difference is in CBD production. This is used by growers who have strains that are 1/2% to 2% CBD and they want to bump that percentage up by half or one percentage points, while getting the THC boost as well. Using the Flower Power, this would mean you run the bulb on for 10 to 15 minutes, then off for the rest of the hour, and repeat throughout the day for a total of 2 to 2.5 hours per day exposure. THC gains are similar to running in continuous mode (below), but you have to be careful to time your work when the lights aren't on, as they are really hard on the eyes. The other consideration is lamp life. Cycling a lamp on and off frequently WILL reduce the life noticeably, regardless of the brand of fluorescent tube.
High level continuous mode. This is the mode we strongly suggest you try. This will get you maximum THC boosting, excellent powdery mildew prevention and remediation, and is proven to slow down insect invasions while you battle them by hand. This usually means running them for 2 hours (or more in some cases) in a continuous fashion. The Flower Power is the bulb of choice for this, being an extremely high UVB lamp, with the remainder being UVA and no visible phosphors in the bulb at all. (You can see a dull, blue plasma glow from it, but that is all) This method puts maximum stress on the plant, but for only 2 hours, so it has 22 hours to recover.
Why "stress" them? Isn't stress bad?
Not all stress is bad. The same reason you use fans to make the plants sway some, to build up strength so they can handle the flower load without bending over and breaking. You are adding stress to the stems to get them to react. It makes them stronger, just like working out the gym tears down muscle in order to build it back up. Stress is everywhere and a necessary part of life for all living things.
In the wild, cannabis is used to being UV stressed and it has created a few ways of dealing with it. First, we have THC. You have to understand that THC is there for a reason, the plant isn't making it for fun, it serves a critical biological role in the plant. The fact that it is medicine and/or can intoxicate you is not why the plant makes it. To understand this, you have to put yourself in the shoes of the plant, and think like it thinks:
UV damages seeds. The only reason the plant is growing is because it thinks it is going to be able to make seeds, thus more copies of itself. Since seeds are exposed, they are vulnerable to UV damage, so the plant has a very good reason to want to protect the flowers, which are the nurseries where the seed will (or normally would) grow. THC has an amazing ability to block UV. The only reason the plant makes THC is to use as sun block. There is no other reason. So by stimulating the plant with UV, you are coaxing it into creating more THC to protect it's (potential) offspring.
The most effective way to accomplish this is by having a moderately short period of very high UVB in the range that will trigger the UVR8 protein, and a long period for the plant to recover. When we do this, we aren't over-stressing the plant at all, we are properly motivating it to reallocate resources into protecting her flowers.
So using a lower UVB lamp for 12 hours isn't stressing them?
It is stressing the plant, just in a different way, assuming you are using a source that triggers UVR8. It's a matter of trickling the stress over the whole day, or hitting it hard and letting it rest for 22 hours. Both methods are effective, just in different ways. The amount of stress is exactly the same, only the time frame is different.
But is this considered organic?
Yes. There aren't any chemicals involved, this is all 100% UV light. It is an all natural way to combat powdery mildew, insects and boost THC. It is no different than growing with LEDs, metal halide or high pressure sodium, it's just supplemental light.
My LEDs (or metal halide) already has UV
No it doesn't, not really. First, all the LEDs that claim to have UV only have light from 365nm-400nm. This is useful for growing leaves and the like, so it is helpful, but triggering the plant requires light in the 280-320nm range, and really in the 280-290nm range. No LED manufacturer has a worthwhile LED that produces light in this frequency range. If they did, we would be selling it, we aren't married to glass tubes, and we already do a lot of contract work with LEDs in other industries. We talk to at least one manufacturer a week about this, no one is making them. There are some serious technical hurdles to tackle before they are available. As of 2019, the diodes burn out fast and have efficiencies in the single digits, so we are likely at least 3 years away.
The same is true for metal halide, which has about 1/2 of 1% UVA in the lower bands, and no UVB or high band UVA. High pressure sodium has zero UV of any kind.
I don't NEED UVB to grow good cannabis
It isn't about need, it is about maximizing the potential while being proactive about mildew and insects. Of course you can grow great cannabis without UVB. And if you use a cheap UVB bulb, it will be just a little better. If you use a great UVB bulb, it will be measurably better. The plants are used to getting UVB. Indica strains in particular expect high levels of UVB because they trace their genes back to the high Kush mountains, where there is little atmosphere to filter the UV. When you grow indoors, they aren't getting what they are used to getting in the way of UVA and UVB. Adding Flower Power is just how you restore the plant to what its genetics were tuned for; what evolution has trained them to tolerate.
If cannabis is used to UVB, why are you calling it "stress"?
We are giving the plants more UV than they typically would get in nature, but for a shorter time. We try to find the limit it can safely handle without causing harm. As I stated earlier, stress isn't a bad thing, as long as you don't over stress them. This is true whether you talk about UV or anything else, as you are trying to get the most from the plant. In order to get the plant to react strongly to a stimuli, you must provide a very strong stimuli, even if it is only for a couple of hours. We have tried everything, and found this to be the singular, most effective way to get total THC of up to 30% or higher. Now keep in mind, total THC is still more a matter of genetics than lighting, but proper UVB stress will milk the most from those genetics.
What about yield?
As long as you are running 2-3 hours at 18-36" from the plant, we haven't noticed any difference in average yield. If you push it harder, you can affect yield. It's hard to say exactly how much because no two plants are the same, even if they are clones, but our indications are that if you push it to the total max, (in this case, 6 hours a day) then you definitely get more THC but you hurt yield by up to 10%. This is hard to test for, but that is our best information.
So if you use as directed for 2 to 3 hours, then yield will be the same, just more of it will be THC and less of it will be green matter. We haven't seen any combination that increases yield. This doesn't mean it can't, it just means we haven't really tested for it or had anecdotal evidence to support it.
How does the penetration level of Flower Power compare to other UVB lamps
Kind of a trick question. UV has a low penetration power because it is a very small wavelength. It doesn't matter what brand of lamp, whether is a glass tube or LED, penetration for a given wavelength will be the same regardless of source. This is one reason we use a 4 foot bulb. If placed properly, you can get some coverage on the lower leaves. If you use FOUR in a 4x8 tent, you can angle them in and hit the lower flowers almost as hard as the upper flowers. Anyone that says their UVB lamps have better penetration is either pulling your leg, or lacks the sufficient education in physics to be speaking about it.
As long as I stress the tops, the whole plant will react and make more THC, right?
Yes, and no. Yes, if part of the plant gets UVB in the 280-290nm range, the whole plant will react, even parts that didn't get direct UVB. If you use a lamp that doesn't produce 280-290nm (reptile lights, and lamps other than Flower Power based), this is not nearly the same. Even if you use Flower Power and put a lot of 280-290nm on the tops, you may get moderately better results down low, but only half as much as if you hit the entire plant with UVB. This is why we like to use multiple lights in a criss-cross fashion. This angles the light between layers of the plant, and gives better coverage, and triggers even the mid and lower flowers to produce more THC in a significant way.
So stress the tops and you will great great results up top and good results down low, but if you can afford some extra fixtures, you can expect better results if you angle them in a bit and get max coverage on the entire plant.
You only need to stress the plants for the last two/three weeks of flower
Not exactly. Will that help? Sure, and it is certainly better than not using UVB at all, but it is far from optimum. We recommend starting at day 1 of flowering for most people, and starting a month before flowering if powdery mildew or insects are a previous problem. There are several advantages to running the entire flowering season.
Starting from day one means the plant has time to adapt to the UV and you aren't harvesting a plant that is a bit in shock. Keep in mind, in nature, you harvest in October, when there is very little UV. By starting out from day 1, you will begin to get trichomes much sooner (a couple of weeks) and the plant will literally change it's "growing mode".
When a plant get regular, high dose UVB, it will be less leggy and a bit more compact. This is normal. You are forcing the plant to create more clear matter, and it isn't magic; that energy must come from somewhere, so it comes from stem building. This will not affect the flowers (buds) themselves, it will still grow just as many, just as large. After all, the plant wants to reproduce, and the UVB doesn't discourage it, it only forces it to spend more energy in protecting the buds with THC, which has an extremely high absorption rate for UVB/UVA. Starting early means getting the most out of your lights, and your harvest, while the plant is kicked into "defense mode".
So use as much or as little as you want, but there are good reasons why we say 2 hours a day starting at day one of flowering. History (and hundreds of growers) have convinced us this it the most effective way to jump up THC production.
What does UVB stressing do to the terpenes?
That is a very hard (and expensive) thing to measure. We do not have hard data on it, so I can't swear one way or another. We have had dozens of people comment about it, and they all said they believe it increases terpene production. Terpenes are defensive chemicals, so that would make sense, but again, we don't have hard data. We have never had anyone say they though it DECREASED terpenes. Our best guess is it will do nothing or increase them moderately. This may also be strain dependent, so it might do nothing for one strain, and improve another.
- Dennis Brown