Does 48 Hours of Darkness Before Harvest Increase THC?

Why

I've grown and harvested both ways, with and without turning off the lights for the last 48 hours. I couldn't tell a difference. That's my experience, not a lab test.

The idea is that a last-minute stress makes the plant produce extra resin. But seeing frostier buds wouldn't tell you how much THC is in them. I couldn't find a controlled study comparing a final two-day blackout with plants kept on their normal light schedule.

A 2023 study of high-THC cannabis found that flower trichomes don't all mature at the same time, and different varieties mature differently. Use a loupe to check trichome heads on flowers in several spots. Watch how they change from clear to cloudy to amber, but don't treat a fixed amber percentage as a magic THC target. Research: https://doi.org/10.1186/s42238-023-00178-9

If the flowers need more time, keep them on their normal light schedule. If they're ready, harvest. A 2025 study found total THC varies among buds and across different parts of a plant, so one lab result would not prove a blackout works. Research: https://doi.org/10.1038/s41598-025-06962-2 Neither study tested a final 48-hour blackout.

My take: skip the 48-hour blackout. Put your attention on flower maturity and a careful harvest instead.

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