Originally Posted by Newbie95
I've heard a lot of people say they leave their plant in darkness for the last 24 to 48 hours before Harvest I was wondering what the purpose of this is
Perhaps nothing more than an old wives’ tale; however, harvesting during the dark cycle isn’t.
I do it more so out of routine than anything else. Running a multi-strain garden from seed it’s easier to remove plants for darkness to then chop later outside the flower room instead of potentially disrupting light cycle to chop a plant or two. Additionally, the "dark room" is also maintained at a much lower humidity than the flower room.
Following quotes are from High Times:
"Lowering the humidity in the room on that last night before harvest morning will ensure increased resin production, without having to let the medium go bone-dry first. Additionally, some growers like to subject their gardens to prolonged dark periods of up to 24 hours just before cutting, claiming they notice spikes in resin production. This is all right as the low humidity will cut down on light uptake anyway, plus it helps to make sure liquid foods within the plants drain down to the root zone."
What time of day to harvest?
"Timing the harvest is Paramount to the final quality. Harvest your precious buds in the dark, just before the lights normally come on. If possible, do not allow the plants to see direct light as long as their roots are attached. Direct light on a plant will draw up stored starches and sugars from the root system. During the nighttime hours, our ladies are busy storing food down in their root system that they made during the daylight hours. During “lights out,” starches and sugars produced by photosynthesis during the day drain downward to the roots. Knowing this, it is easy to figure out that you want to cut your plants away from the roots before the lights come on, when food moves back upward into the buds. Outdoor herb is often harvested during the daytime hours and the result is a harsh, difficult burn and an extra long cure. The starches and sugars present in daytime-harvested herb act like fire retardants—not the effect we’re looking for. In addition to tasting and burning bad, these fire retardants also change the chemical make up of the smoke you’re ingesting. This means that the THC, cannabinol, cannabidoil and other active cannabinoids can’t burn at the perfect temperature to get you properly high because they haven’t properly converted to their psychoactive forms."
The excerpts from HT were just the most readily accessible, but I have read more "technical" writings over the years about the importance of a night time harvest - so it's doubtful a couple days darkness hurts anything. But does it increase THC? You'd have to run clones and harvest accordingly to submit samples to a lab. I look a plant over before putting into dry darkness and feel that resin often does increase by the time I chop - but I could just be really high!