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Light deprivation for cannabis crops

Humans have been trying to trick nature for a very long time. Horticulture itself was born out of the necessity to overcome natural limitations and thus being able to grow crops during winter times, for instance. Over time, many techniques have been developed in order to get the most out of a given crop. These techniques usually trick the plant into believing that there are specific external conditions which make the plant reacts in a unique way. Flowering plants, for instance, can be forced to start flowering earlier than it is supposed to through ‘light deprivation. “Light deprivation is carried out by covering the crop through curtains that are placed over a frame, which could be the greenhouse itself, or a structure built specifically for that purpose”, explains Eric Brandstad, founder and owner of Greenhouse Advisory Group, a company specialized in greenhouse consultancy and rescue. In addition to that, Eric is a professor at the Oaksterdam university in Oakland, where he teaches and organizes curricula on cannabis cultivation. He continues, “People started doing light deprivation within greenhouses rather than in indoor farms as the former are affected by sunlight. Therefore, since it is not possible to turn off the sun, growers needed to find a way to choke it out."

“The vegetative state asks for 18 hours of light and 6 hours of darkness. To start the flowering phase, it is necessary to switch to 12 hours of light and 12 hours of darkness. However, through light deprivation, it is possible to make this happen at an earlier time than it is supposed to”, Eric explains.  Of course, light deprivation techniques are not the same for open fields, greenhouses and indoor farms, and at the same time, they are not always equally effective. First of all, because cannabis growers are not usually as knowledgeable as their colleague from horticulture, according to Eric. “This derives from the fact that a lot of people jumped into the cannabis industry without any previous knowledge. Therefore, they learn as they go.”

Different types of light deprivation
According to Eric, light deprivation works better in greenhouses than in open fields or indoor. He says that the reason is that greenhouses have a frame for curtains since the beginning and they utilize natural sunlight. Therefore, the covers can be pulled over just a few hours before dusk, thus only slightly anticipating the normal course of the sunlight. “We are still learning a lot about this stuff, but there are a few things that we are sure of”, says Eric. “One of these is that indoor farms are more susceptible to light leaks, which negatively affect the plant growth. These can occur for example if there is some mistake in the growing facility or maybe only because one forgets to close the door completely. This would not happen in greenhouses because one can just lower the light deprivation curtains a few hours before dusk. In this way, it is impossible for the light to get into the growing room as the sun goes down, while indoor rooms are artificially illuminated and thus the risk of light leaks increases.”

“However, there still some things to fully understand with regards to cannabis growing. For instance, light leaks do damage cannabis crop, but we still have not figured out to what extent this happens”, Eric points out. According to him, there are companies both in the US and in Canada that do not follow the same procedures in terms of the number of layers they use to cover the growing facility: “Historically, growers have been using three-layered protection to stop the light. Of course, this comes at a cost. However, some Canadian companies are using only two layers, which allow a little light to pass. However, they saw that plants did not experience any issues. On the other hand, in the US, growers keep using three-layered protections. So, there is still quite a bit of uncertainty in terms of how much darkness a cannabis plant actually needs.”

Internal and external light deprivation systems
Eric takes care to explain that there are different light deprivation systems. These can be either internal or external the greenhouse, and they can also be activated either automatically or manually. “Most greenhouses we see these days have a shade screen inside. So, a lot of times the light deprivation curtains mimic or going at the same pace of the shade screen. This is a bit more reliable and efficient”, Eric says. On the other hand, “External light deprivation systems usually requires a bit more work as the system is exposed to the weather. Even if it were automated, sometimes it is necessary to take care of that manually, as climate could change the time when it is required to lower the curtains.”

Greenhouse rescue
Eric is also specialized in greenhouse rescue. According to him, many cannabis growers face numerous issues which could potentially compromise the entire greenhouse. “Three are the most recurring problems among growers: ventilation and air-flow within the facility, as climate control is extremely important; workflow strategy; and mostly, cross-contamination. I have seen that many problems struggle with keeping the work environment clean, and this is a very big problem especially from a pharmaceutical standpoint.”

For more information:
Greenhouse Advisory Group
[email protected]