Led by Professor Bruce Bugbee in the United States, Utah State University (USU) has been at the forefront in cannabis research, specifically in the cultivation and sale of medical hemp. Known for his work with NASA and the cultivation of crops beyond Earth, Bugbee is a self-proclaimed cannabis myth-buster who prides himself on his research into the fascinating crop.
While Bugbee’s research is still legally within its infancy — thanks to the 2018 Farm Bill — he and his team are already turning up results that will make the vast majority of cannabis growers take heed.
Irrigating Cannabis Is No Different From Other Crops
Transitioning to a high phosphorus fertilizer for the flowering stage of cannabis is a common growing practice promoted by both commercial gardeners and de facto sages in the field. However, within the last few years, more and more cannabis growers are finding success in running a single NPK ratio throughout all growth stages. According to Bugbee and his team’s research, they may be on to something.
Bugbee isn’t one to mix words, saying a 20-10-20 (nitrogen-phosphorus-potassium) fertilizer like Jacks or Peters is best for all stages of cannabis growth when combined with a drain-to-waste peat/vermiculite-based media with supplemental dolomitic lime and gypsum. Other substrate mixtures like coco-coir and perlite work nearly as well, but Bugbee’s is quick to mention the importance of introducing a silica additive in the absence of vermiculite. Bugbee and his team have found increasing phosphorus beyond his recommendation serves no purpose except to pollute the environment.
Bugbee says he and his team find an EC of 1.2-1.3 mS/cm can be given throughout all growth stages. Growers should aim for a 10% runoff that reads between 1-1.5 mS/cm to prevent salt buildups and ensure proper irrigation. Variations in watering frequency determine the overall amount of fertilizer applied.
Efficacy Is More Important Than Spectra For Yield And Cannabinoids
Since their introduction into the world of sole-source lighting for crops, LEDs have been touted as superior to all other lights, namely the king of grow lamps, high-intensity discharge lighting, or HIDs. And while many will acknowledge that these claims were perhaps premature, within the last few years it’s become apparent with the latest advancements in LED technology they were ultimately right.
However, proponents of HID lighting have stuck to their guns, claiming that the UV and far-red photons their lamps’ output deliver a higher quality bud. However, Bugbee and his team say, not so fast. Despite the 2% increase in far-red and introduction of UV light, Bugbee’s found no improvements in cannabinoid levels in cannabis plants grown under HID lamps vs. cool white LEDs.
Temperature Has Major Implications On Cannabinoid Concentrations
Perhaps USU’s most notable finding has been their research on temperature and its effects on yield and cannabinoid concentrations. A slight increase in flower yield was noted when increasing temperatures from 73F to 84F. However, before growers rush to increase temperatures, they should, instead, take a pause and consider lowering them.
When increasing temperature from 73F to 84F, researchers noted close to a 50% decline in cannabinoid concentrations, with a significant drop occurring once temperatures exceed 80F. While the USU team cautions they aren’t sure what to make of this, these findings should make every cannabis grower take serious note.
It appears their findings come from cannabis crops grown under LEDs, where the common advice is to keep temperatures about 5 degrees higher than HID — between 80-85F — due to their lack of infrared light. This is the range where the biggest decline in cannabinoid concentrations has so far been seen.
Growers May Be Harvesting Too Late
An 8-week flowering time or 56 days after initiating a 12/12 photoperiod has long been the commercial wisdom when it comes to harvesting cannabis. However, within the last few years, many longtime growers, including myself, have promoted caution about harvesting so soon, recommending growers wait until their plants are typically 9-10+ weeks into flowering before harvesting. According to research out of USU, we all could be wrong.
In multiple studies led by Mitch Westmoreland, he and his team have found examples of multiple phenotypes peaking in both THC and CBD concentrations about 40 days after the start of their inductive photoperiod. While ratios of THC and CBD were generally constant throughout the trials, by day 60 and beyond, the team noticed a notable decrease in both THC and CBD concentrations when compared to their peak around day 40.
Westmoreland doesn’t say if growers should start harvesting sooner than typically advised but notes the significance of their findings and that they need to further investigate the issue.
Drought Stress Isn’t A Friend Of Cannabis
Cannabis’ demand for water has long been a thorn in proponents of the crop’s side, with naysayers warning that increasing production could have devastating impacts on the environment. As such, many of the environmental-conscience cannabis growers have made it a priority to reduce water use whenever possible. However, while a noble pursuit, they should tread carefully.
According to USU’s research, water-stressing cannabis plants directly correlated to a decrease in flower yield. Fortunately, cannabinoid concentrations were not seen to experience a decline, and plants were found to bounce back quickly when given adequate water.