Light deprivation can help cannabis growers looking to dial-in control, add more harvests to a production cycle and protect their plants from outdoor contaminants.
The technique, which involves using tarps or curtains to block out sunlight—typically in greenhouses or hoop houses—is growing in popularity as cultivators work to maximize production.
Light deprivation pushes cannabis plants to start the flowering process. To accomplish this, growers use shade cloth or other materials to allow in only 12 hours of sunlight, mimicking the amount of sun a plant would receive in a natural setting during the flowering phase.
“Every advantage a light-dep grower can eke out—lower cost of production, more harvests per year, something to mitigate the smoke damage—all adds to their long-term viability,” said David Kessler, vice president and head of horticulture at Agrify, a producer of indoor-farming equipment in Burlington, Massachusetts.
According to Kessler, the operation can be as simple as pulling a tarp over a hoop house at 5 p.m. and pulling it off again at 5 a.m.
In addition to light deprivation, that layer can partially protect plants from smoke, hail and torrential rain.
“The biggest advantage is adding a level of control to outdoor cultivation,” Kessler said.
At High Life Farms in Chesaning, Michigan, Head of Cultivation Don Newman said light deprivation allows each room in his greenhouse cultivation operation to be harvested 51/2 times per year. With three flowering bays in the operation, High Life harvests between 15 and 18 times per year.
Newman’s greenhouses all use mechanical curtains in a fully automated system.
“It really helps to keep a more consistent environment like you would see indoors,” Newman said. “Even on cloudy days, we’re able to benefit from the sun.”
Newman likes to use Kush and OG varieties because they consistently finish at around 60 days and work well with High Life’s growing system.
According to Newman, the quality of cannabis grown outdoors using a light-deprivation system can be as good if not better than indoor-grown marijuana, as the plants receive extra UV rays from the sun, which helps them develop terpenes and cannabinoids.
Light-deprivation ensures that outdoor growers maximize the amount of time available for sun-grown cannabis and don’t fall victim to the weather, said of Humboldt, California-based Kristin Nevedal, chair of the International Cannabis Farmers Association.
She pointed out that a lot of cannabis growers in the mountains of Northern California get only one crop per year, so it’s important that it comes in on time. The set schedule offered by light deprivation also means that growers can plan around a definite harvest date and adjust their operation accordingly.
She agreed that cannabis grown with light-deprivation techniques can yield superior flower.
“It gives you an opportunity to produce very high-quality material,” Nevedal said.
She also prefers the way light deprivation allows growers to finish plants at a consistent size, say 3-4 feet, meaning workers aren’t struggling to take down much larger plants.
Using hoop houses with tarps can help ensure the plant doesn’t take too long to flower, which could put the harvest at risk for early frost, fall-season wildfires or rain and resulting moisture problems.
Nevedal said the growers with light-deprivation structures had additional protection against ash falling from wildfires that ravaged the West Coast last fall.
Dr. Jordan Lewis, CEO of Fotmer Life Sciences, a cannabis cultivation and extraction company based in Montevideo, Uruguay, called light deprivation a “fundamental tool.”
His team uses the technique in specially designed greenhouses with mechanical curtains to create two harvests where it would otherwise have only one.
Lengthening the harvest window allows Lewis to spread out the processing segment of the labor flow, cutting back on the need for seasonal labor and ensuring employees have enough work to stay busy.
Fotmer Life Sciences is growing in 18 different greenhouses right now, and the set schedule allows them to stagger the harvests, which helps with managing the labor needed for trimming and curing.
“We don’t have as many bottlenecks,” Lewis said.
He also points out that staggered harvesting is a risk-management tool: For example, shortening the life cycle of the plant by adjusting the light can help to prevent contamination between batches.
“The shorter the life cycle of the plant, the less opportunity (there is) for disease to be impactful,” Lewis added.
Another tip: Light deprivation does not permit a lot of room for error. A pinhole of light getting through a curtain can cause plants to herm and go to seed, ruining the whole crop.
“You have to make sure there’s no light, or you don’t get the results you need,” Lewis said.