I’ve heard this one from different growers over the years, but for now, the jury is still out. The idea is that a cannabis plant needs to remain in the vegetative stage for at least 8 weeks before being switched to the flowering stage in order to reach its maximum THC levels when it starts budding. Cannabis plants which have been allowed to grow for at least 8 weeks in the vegetative stage tend to be much bigger and more robust than plants switched earlier, and they produce far greater yields. But does that mean that they produce higher levels of THC?
It seems like it could be possible, but it might also be related to other factors. For example, big plants are usually grown under powerful grow lights, which affects potency, and are also often grown by more experienced growers. My idea for a test (hopefully someday I’ll get to do this when I get more room to grow!) Sprout several seeds from a very stable cannabis strain like Northern Light to reduce genetic variation between the plants Allow each seedling to grow out to 8 weeks in the vegetative stage, then take a clone off each plant. Although clones are the size of seedlings, they are the same internal “age” as their mother so in a way, these clones would already be 8 weeks old Sprout more seeds of the same stable strain and grow them until they’re about 3 weeks old so they’re the same size as the clones. You want to time this so that the seedlings are about 3 weeks old just as the clones are the same size and taking root. Seedlings can’t start flowering before 3-4 weeks old and we’re trying to create as close to the same conditions as we can between the two plants to reduce as many variables as possible. Now that you’ve got your 3-week seedlings and your “8-week” clones that are the same size, flower them together in the same conditions. If the buds from the clones are more potent than the ones from the seedlings I’d say it’s pretty good evidence that increased age increases potency. If not, well, back to the drawing board to try another test!
Letting plants get older before the switch to the flowering stage definitely results in bigger plants and higher yields, but we don’t know if it increases cannabis potency! Lack of Pollination (Producing “Sinsemilla”) Just a few decades ago pretty much all cannabis bud you could find was full of seeds. This is because at the time many growers didn’t realize that male and female cannabis plants need to be separated in the flowering stage to prevent the female plants from getting pollinated and making seeds. However, once cannabis growers became more aware of growing techniques including how to prevent pollination, there was a rise in “sinsemilla” weed, a word which combines the Spanish word “sin” (without) and “semilla” (seed) to mean cannabis “without seeds.” Seeds belong in your garden, not in your buds! The sinsemilla bud that started flooding the market was much higher potency than the seedy, low-quality bud that had been available before. This led to the term sinsemilla being used to describe very high quality and potent cannabis. There’s no doubt that most growers prefer buds without seeds, but the term sinsemilla has led to the idea that cannabis buds without seeds were inherently more potent than seedy bud. While this may very well be true, there isn’t much evidence that it’s actually the lack of pollination which caused the dramatic increase of potency experienced by cannabis enthusiasts at the time. Right around the time growers started producing non-seedy buds, the cannabis breeding scene was also starting to get established. Publications to assist cannabis growers like the High Times magazine appeared on the scene to help growers learn better growing techniques, and cannabis breeders like Nirvana started shipping cannabis seeds of famous strains to growers all around the world by mail order. Growing and breeding techniques were improving simultaneously. It’s possible that the increase in potency experienced by people who switched to seedless buds was actually the result of better genetics/breeding. These days, most people only get sinsemilla and no one really wants to do direct comparisons. However, keeping buds from producing seeds will dramatically increase the perceived quality of your buds, as well as your yields, so regardless of whether it increases bud potency or not, it’s something every grower wants to do! Don’t let your female plants get pollinated – remove all male plants from your grow room immediately (or start with feminized seeds, which don’t produce any male plants)! Type of Grow Light & Spectrum – HPS, LED & LEC Grow Lights. Different types of grow light produce different spectrums (colors) of light. There are some growers that believe that growing cannabis under the unique light spectrums of LED grow lights or LEC grow lights may increase resin production and THC levels. Other growers swear that you need powerful HPS grow lights to produce the highest levels of THC. During the flushing process of growing cannabis, a grower generally gives their plants just plain water for the last few weeks before harvest. This is done to encourage the cannabis to “cannibalize” itself and use up all remaining nutrients in the plant. The idea is to get the plant to use up any nutrients that may have built up in the buds which could possibly affect that taste/smell after harvest. However, there are several additional types of flushes that many growers believe will increase THC levels. Most of these are done in addition to regular flushing, just before harvest. Unfortunately, there aren’t many (if any) tests determining which one of these work, but there are many experienced growers who swear by these methods! Unfortunately, they don’t all match (for example some growers say to harvest in the morning, while others believe you get more THC if you harvest during the plant’s dark period), but these are the most common flushing techniques that I’ve heard to increase THC levels right before harvest.
These “flushing” methods may (or may not) increase THC: keep plant in the dark for 2-3 days before harvest harvest cannabis in the morning harvest cannabis during the plant’s dark period water plants with ice water before harvest chop down and hang entire plant upside down for a few days before trimming and drying buds. I wrote this section after reading the results of a 6-year study about industrial hemp.
Although hemp is closely related to the cannabis, they’re not the same thing so these finding should definitely be taken with a grain of salt.