Finding reliable genetics has been one of many burdens for the blossoming hemp industry. That is, in part, because many genetics available on the market are photoperiodic, meaning they need to be exposed to darkness for a specific amount of time to trigger flowering. Since day length varies by latitude, genetics that perform well in one geographic region may not grow well—or at all—in another. (For more information on photoperiodic varieties, visit bit.ly/HG_photoperiodism.)
As a possible solution to the problems that come with day length-sensitive varieties, some hemp growers are exploring autoflowering genetics. Instead of flowering after a set period of darkness, these varieties flower after an amount of time that isn’t dependent on light levels.
Larry Smart, Ph.D., head of Cornell University’s Hemp Research Team, has spent the past two years researching autoflowering hemp varieties used for cannabinoid production.
“I still think that’s one of the biggest challenges [in the industry] right now is developing varieties that have flowering times matched to specific latitudes,” Smart says. “Companies have been actively marketing and promoting autoflowering varieties to growers, so we want to make sure that we’re doing some science-based testing and providing non-biased information to growers.”
When Smart began trialing autoflower varieties in 2019, he experimented with two CBD varieties from hemp breeding company Kayagene. He started these from seed in the greenhouse and planned to transplant them into the field after 15 days, as recommended by the company. But from the start, the genetics came with a learning curve.
“If they experience any stress at all, which is not uncommon in a greenhouse, then they will be triggered to flower,” Smart says of autoflower varieties. “Our fields weren’t ready on day 15, so I think we went until day 20, and they had flowered by the time we transplanted them.”
Because hemp growth slows considerably when it begins to flower, Smart says, the crops remained small and did not produce much floral biomass.
He headed into 2020 with double the number of autoflowering varieties (again, all for CBD production). This time, he decided to direct-seed them outdoors and use an overhead irrigation system.
“I would say that trial went very well just in terms of overall agronomy,” Smart says. “We’re still analyzing the data in terms of yields and cannabinoid content, but I was quite pleased with the way we were able to get that established.”
He planted all the autoflowering varieties with only 30 inches between rows and about a foot between plants in the row. This is tight spacing compared to the typical 24 square feet—6 feet between rows and 4 feet between plants—given to day length-sensitive cannabinoid varieties, he says.
Smart found the autoflowering varieties can handle the tighter spacing because they flower quicker than many day length-sensitive varieties, which keeps them at the smaller size.
And while he hasn’t yet analyzed the yields for 2020, Smart says based on trials the past two years, autoflowering varieties appear to overall have a higher proportion of flower biomass to total plant biomass than photoperiodic genetics. While a typical day length-sensitive variety produced about 50% of its total dry biomass as flower, the floral biomass of the autoflower varieties was 87% of their total dry weight. This ratio—also known as the harvest index—is a key target for breeders to maximize allocation of plant resources to flower production, Smart says. (For more results from Cornell’s 2019 hemp trials, visit bit.ly/Cornell2019HempTrials.)
Because of these varieties’ higher ratio of floral biomass and their ability to thrive in tighter spacing (allowing more plants per acre), Smart is now working to learn more about how autoflowering variety yields compare with their day length-sensitive counterparts.
There are also other unknowns: For instance, if day length does not trigger flowering in these plants, then what does? Autoflowering genetics typically have a minimum maturity time, which means they have to grow at least a certain number of days, no matter what the light conditions are, in order to flower. But as Smart learned in 2019, other autoflowering genetics appear to have no minimum maturity time at all—seedlings could flower in a matter of days.
“That’s something we really want to try to do more research on to understand the genetic basis for that maturity requirement,” Smart says.
Day length-sensitive cultivars can also have variation in maturity times, even within a variety. Smart says that’s a big issue he’s seen while trialing day length-sensitive CBD varieties.
“Day length sensitivity is not something that is very well-described for many varieties,” Smart says. “... Variation in flowering time is a real problem for growers. If 25% of plants flower early and the other 75% flower four or even six weeks later, it’s harder to get maximum yield at harvest time.”
This is perhaps one of the largest potential benefits of autoflowering varieties. If researchers find uniform maturity requirements within autoflower varieties, farmers across the country could theoretically plant them without succumbing to some of the largest issues they face growing photoperiodic varieties, such as inappropriate climate and day length.
Additionally, Smart says hemp greenhouse growers could use these varieties to move through multiple production cycles a year without light deprivation shading, as autoflowering genetics are not dependent on a specific night length to reach maturity.
Ultimately, though, researchers still have much to learn about autoflowering varieties. Smart says growers who want to try autoflower varieties should consider how they plan to harvest. A mechanical harvesting system, for example, may be incompatible, as the plants are too small to feed properly through the equipment.
“You want to try to match plant size with your harvesting system,” Smart says.