Light deprivation is not for the weak. Unless you’re using an automated solution-it takes physical strength to pull those tarps for weeks even months. Even if your solution doesn’t require brute strength, it takes dedication and attention to detail to pull off a successful light dep. harvest. You can’t be late to the game even once. You show up late or provide anything but consistent dark periods and you will stunt your plants and/or force seed.
First and most important, buy the right tarp for the job, one that is built tough for the long haul and constantly make sure there are no holes in your tarp–even a pinhole can ruin your efforts. Keep your tarp nice and never walk on it, be sure there are no catch points to rip or poke the tarp. And pull with two hands so you don’t rip it–place your hands as far apart as comfortably possible to allow for the most leverage and least rippage.
Once you have pulled the tarp be sure to tuck and fasten it appropriately so that absolutely not a particle or wave of light can enter. Then go in the greenhouse to inspect for light discrepancies each time you pull, even if you use a push button solution you never know what might have folded or kinked, cat clawed or pecked by birds. If you’re going to take all that time and/or invest all that money than you might as well pay particular attention to detail to make sure your dark period is consistently dark. Be sure not to use those extension cords with the light up ends anywhere within your structure. Even this small LED light will force seeds on nearby branches. Now that you have achieved a totally dark environment you have to find a way to get fresh air circulating in the space without compromising the darkness. You can rig something to bend the light on louvres and intake fans or you can go pro.
The kind folks from Forever Flowering Greenhouses have solved this problem, engineering what they call the Breathable Wall, a solution for using louvers and outside fans without letting light in during the deprivation cycle. The Breathable Wall can simply be retrofitted onto your structure, or be methodically planned into your next greenhouse project and is your best bet to make sure your ladies have that critical fresh air intake.
I don’t recommend trying light dep. unless you are totally serious and fully dedicated to the process for whatever reason. If you are growing at a spot other than where you live than consider you need to be at that spot every day, on time, like clockwork or your efforts are futile. It can be a very rewarding process if you are dedicated and pay attention to detail. And like any cannabis growing experience, don’t expect to be successful right out of the gate. You will learn a lot the hard way, but don’t be discouraged by the dark side.