Back in Black: The Basics of Light Deprivation Cannabis Cultivation

By Kent Gruetzmacher
Published: May 4, 2018 | Last updated: November 25, 2021 07:25:25
Key Takeaways

Tricking your herbs, vegetables, or flowers into thinking harvest time is approaching through light deprivation can result in more frequent high-quality yields. While becoming popular, light deprivation greenhouses take some dialing in. Kent Gruetzmacher sheds some light on the basics of blackout gardening.

The popularity of light deprivation cultivation has been on the rise over the past few years. There are several reasons why, but key factors include higher quality yields and off-season harvest times, allowing growers who utilize this method to supply the market with a particular product when others can’t.


In light deprivation growing, horticulturalists use sunlight to fuel their gardens while simultaneously employing environmental controls not seen in traditional outdoor grow scenarios. This blend of cultivation styles allows light deprivation gardeners to combine their knowledge of indoor and outdoor growing to produce exceptional crops. Furthermore, light deprivation requires less electricity and allows for harvests during better weather.

Plant Photoperiods

The most definitive characteristic of light-deprivation cultivation is the artificial simulation of equal 12-hour light/dark photoperiods. Using light deprivation, cultivators seek to mimic the photoperiods of the late summer and early fall which triggers plants to produce flowers. This idea of artificially induced flower periods represents a merging of outdoor and indoor growing methods.


While indoor growers have timers that simulate night and day in a grow room, light deprivation growers must devise other means to black out the sunlight during the 12-hour dark period. It should be noted, however, that artificial light deprivation methods are only necessary in evening and morning in most areas.

Exposing your plants to sunsets, moon rises, and the fresh air of summer nights will generally improve their quality. With that said, light deprivation enthusiasts must devise blackout systems that cover the entire canopy and exterior of their gardens to block all sunlight in the simulation of night time conditions.

Frames, Hoop-houses, and Greenhouses

No matter how sophisticated or simple cultivators wish to make their operations, all light deprivation crops require an exterior frame which supports a blackout system. There are three routes one can take in the creation of a framework: wood frames, hoop-houses, and greenhouses. Gardeners can create wood frames by placing heavy wooden posts in cement at the ends of the garden.


These wooden posts have heavy cables which support the tarp and allow for it to easily slide over the canopy of the garden. Secondly, PVC hoop-houses can be constructed by pounding two-foot pieces of rebar into the ground at opposite ends of the garden and simply bending the PVC over the canopy and onto the rebar, forming a “hoop.” Finally, greenhouse kits and frames make excellent support over which to pull blackout tarps.

Greenhouses provide growers with the ability to utilize more environmental controls than with wood frames and hoop-houses, and greenhouses have opaque walls as well as door systems, making them more attractive for privacy and security.


Tarp Systems

The sort of tarp-pulling system one chooses for a light deprivation operation will prove to be important for the duration of a flowering cycle. This is because the tarp has to be pulled over the entire canopy of the garden twice a day for an entire 55- to 70-day flower cycle. Therefore, light deprivation cultivators have to be present twice a day, for two months solid, to ensure this task is complete.

In the novice operation, as seen with wooden frames and hoop-houses, it’s often possible to simply pull the tarp over the frame by hand or with the aid of ropes. To aid in this process, growers also devise pulley systems mounted on trees and wooden poles to help with getting a tarp over a large or tall frame system.

Finally, greenhouse companies have designed a number of automated, less labor-intensive systems that black out daylight. These automated systems include motorized tarp pulley systems as well as large blinds that fold over on one another to create a completely dark environment.

Airflow During the Night Period

Regardless of the scope of a light deprivation operation, all cultivators need to consider airflow in their gardens when the tarp is pulled over the canopy during nighttime simulation. This is because the tarp hinders all airflow from outside the canopy, presenting challenges with humidity and subsequent issues with mold and mildew.

To remedy these concerns, growers must employ intake and outtake fans similar to those found in indoor grow rooms to ensure a steady exchange of air when the coverings are drawn. When choosing the size of inline fans for intakes and outtakes, gardeners should use similar considerations as seen with indoor growing.

Exhaust fans should completely exchange the air in a light deprivation garden in five minutes or less. Depending on the size and the structure of a garden, intakes and outtakes can be mounted on the framing system or simply placed on the ground. However, for air to move efficiently, it’s essential that the ducting connected to these fans is long enough so that the ends are not covered by the tarp when it is pulled over the frame.

Light deprivation greenhouses essentially signal plants that seasons are changing earlier than they actually are, so growers can manipulate their crops to produce more robust and frequent crops. Keep in mind that some plants react better to light deprivation methods than others, and that issues such as excessive heat or humidity, lack of oxygen to the roots, and pest infestations can be prohibitive. Once dialed in, however, light deprivation technology can be used to harvest early and often, particularly in late summer and early fall.


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Written by Kent Gruetzmacher | Writer, Owner of KCG Content

Profile Picture of Kent Gruetzmacher

Kent Gruetzmacher MFA is a Colorado-based writer and owner of the writing and marketing firm KCG Content. Kent has been working in the cannabis and hydroponics space for over a decade. Beginning in California in 2009, he has held positions in cultivation, operations, marketing, and business development. Looking specifically to writing, Kent has worked with many of the leading publications and marketing agencies in the cannabis space. His writing has been recognized by such icons as Steve D’Angelo and Rick Simpson.

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