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Greenhouse cultivators have a few different needs, protocols and methods of cultivation over our brick-and-mortar counterparts. Differences such as having systems that create an artificial dark period vs. permanent dark rooms that need electric-powered lights.

By design, greenhouses make the most out of the big light in the sky, simply because the power and intensity of the sun cannot be replicated. (Did I mention, it’s free?) Harnessing that kind of power does pose some challenges, however — the biggest one being the light cycle. Large-scale growers cannot simply slap stickers and tape over the windows to make it dark, which is why greenhouse cultivators use blackout systems to implement the 12/12 photoperiod (12 hours of light, and 12 hours of uninterrupted darkness). This process of regulating light is also known as light-deprivation.

Simply stated, a blackout system is a cultivator’s best friend and one of the most valuable tools in the growers’ arsenal. This makes blackout systems a must-have for any serious greenhouse cultivator, especially those cultivating year round.

I am asked frequently about the implementation and use of blackout systems. Questions range from: What is a blackout system? How does it work? Why do I need a blackout system, and what are the costs associated with owning one? Does the material or thickness matter?

What is a blackout system?

Starting with the basics, a blackout system is a tool — often mechanized, that moves a large sheet of material, frequently a rubberized fabric or type of portable awning — used to block unwanted light. Because greenhouse cultivators use the sun as their primary light source, we need to be able to force darkness, because, obviously, we simply can’t turn off the sun.

What is its purpose?

A blackout system is designed to cause the intentional deprivation of light to a given area. Utilizing the correct duration of light is essential in cannabis cultivation, especially during the flowering period.

Without a strict regimen of 12 hours of light and 12 hours of dark, the plants could continue to grow in their vegetative state, and mutate into a hermaphrodite due to light-induced confusion and stress. These outcomes depend entirely on the intensity and duration of light that is allowed to leak into a light-deprived (dark) area. This is why blackout systems are essential to cultivators’ success.

How does a blackout system work?

Cannabis is classified as a “short day plant.” Meaning, when the length of darkness exceeds that of the cannabis plants’ critical photoperiod of light (short days, long nights), the plant moves into flowering development. The plant’s internal mechanisms trigger the release of proteins — like “phytochrome” and/or “cryptochrome” — because they sense a change in the light duration. (Check out “Phytochrome Signaling Mechanisms,” The Arabidopsis Book | American Society of Plant Biologists.) These proteins tell the plant that winter is coming and it is time to mature and produce seeds, so there is continuity of the species.

Light control is essential so the plants do not express gender confusion, chiefly that of hermaphroditism. If the plants become confused due to the introduction of unwanted light pollution, they can and will cross-pollinate unsuspecting females in the garden. In some cases, a garden may even fully revert to a mutated and stunted form of vegetative growth and cost the grower dearly.

Costs and Considerations

The cost associated with blackout systems depends on a myriad of variables, such as:

  • What is the square footage of the facility?
  • Does the system operate automatically, or manually?
  • What types of materials are used?
  • Is the material prone to wrapping or stretching?
  • Does the material retain heat?
  • What is the material’s measured thickness?
  • What type of maintenance policy or warranty comes with the system, if any?

The answers are important to know before having a blackout system kit installed.

Blackout systems can become more expensive than initially planned for, especially when installed in a rush or incorrectly. I have seen some real nightmares when it comes to DIY blackout systems, so be warned. You’ve heard the old saying, “Some things are better left to the professionals”? That is true here; stick to what you know. If you are not a blueprint-savvy fabricator, my recommendation is to let professionals handle installation.

When I first started working in a greenhouse, the grower I worked with almost burned his entire greenhouse down because he did not follow installation directions. The cost to fix his mistakes was around $1,100 more than it would have cost to hire a professional electrician to do the job correctly the first time. Another example of a DIY mistake is a pulley motor installed upside down and on the wrong side.

Choosing a blackout system can be daunting, especially since so many options are available. I strongly recommended consulting with a professional. Do thorough research; it will save you time and money in the long run. And if you don’t, you’ll risk getting confused hermaphrodite plants, and a garden full of unwanted seeds. I don’t know about you, but I’m not ready to be a grandpa just yet.

About the Author: Michael Sexton is the founder/CEO of Mile High Genetics, a Colorado-based, veteran owned and operated company that specializes in veganic, pesticide-free cannabis breeding and genetics. Sexton, a former Combat Marine, has more than 10 years’ experience growing cannabis and is especially skilled at growing at high elevations.