SD Cannabis grown in a light dep greenhouse
SD Cannabis grown in a light dep greenhouse in the Emerald Triangle.

Light leaks within the light deprivation world aren’t as big of a deal as they are for indoor growers. Indoor growers tend to have light leaks that are near constant, 12-18 hours or even 24 hours depending on the scenario. Light leaks in this capacity can definitely be a problem and that has been proven.

Light leaks in a light dep grow or greenhouse are another story. I’ve pulled manual tarps for many years with significant light leaks, and I can easily say I never had a problem. But does that mean I’m pro-light leaks? Certainly not, but depending on how things are set up, light leaks can occur from something as simple as the wind disrupting a section or a corner. No need to worry if this is something that happens once in a while. Everyday occurrences could effect the plants closest to the light leak but intermittent mishaps won’t have a noticeable impact.

Another factor to help create confidence is knowing its getting dark. That light leak will gradually diminish into darkness. Unlike the indoor scenario that stays well lit till the timer turns off. Lucky for us light dep growers, we can work with mother nature naturally to get the results we are looking for.

Use a Light Meter to Check Your Dep

In my opinion, the best method for times to pull tarps is the early evening shift. Using a light meter can help determine accurate times for your particular garden. Not one garden is the same — some are blocked by mountains, trees or maybe there’s no obstruction but light levels can differ. The light meter is only needed to let us know when we have registrable light. When we see the meter go from zero to 1 we know we have measurable light.

We must use a meter since plants are less sensitive to light than human eyes and require measurable light to begin photosynthesis. Once we have the light meter picking up light first thing in the morning, we now know that in 12 hours time the dep curtains need to be closed.  It doesn’t matter if the sun is still out. Anytime longer than 12 hours over a long period of time will not help ensure proper finishing (quality, timeline).

Its best to use a white exterior tarp to help reduce any solar gain. I’ve tested surface temps on aluminet, silver and black tarps and they all read higher surface temps than white. We don’t need to encourage more heat while we suffocate the plants…

Once the curtains are closed, we can use the light meter one last time to see when its officially dark. Don’t get me wrong, it’s pretty obvious when it’s really dark but my goal is to get the plants uncovered as soon as possible to encourage the natural airflow. Usually the last lumen or zero on the meter means the plants are in the dark but typically we can still see without a flashlight. I usually start to uncover around 5 lux on the meter because by the time I get to the last portion of the tarps the light has gone down to zero.

What Happens When You Forget to Pull Tarp a Few Days?

It takes a lot of missed days and constant light leaks to make a plant revert. I haven’t always closed the curtains at the exact same time every day. The timing fluctuated by 15 mins here and there, and I also missed five days during a round two years in a row — not all at once but within a two month period. This caused zero problems.

The last bit of info I’ll leave you with is using the light meter inside the grow area while the curtains are closed. You might see some light leaks but if it’s not measurable then its not effective in reverting plants. Don’t forget the moon and stars can be very bright throughout the growing season, and we’ve never heard of issues related to lunar activity.

Don’t Work Harder Than You Need To

If you pull 7-to-7 or 8-to-8, it’s usually causing more problems than good. Growers are working harder and most of the time the plants ultimately suffer if there is not proper airflow throughout the dep period. Quality and efficiency are the main reason for the “close at dinner, open at bedtime” ritual, as I call it.


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