Short answer
Most photoperiod cannabis flowers for about 7–10 weeks counted from the first pistil clusters, so harvest lands about 9–12 weeks after the flip. House position: the flip isn't day 1 of flower. A transition of about 10–14 days comes first, so a breeder's "8 weeks" usually means harvest 9.5–10 weeks after switching to 12/12. Supported.
Why
Switching to long nights starts floral induction, not flowering. The shoot tip spends the next week or two rebuilding itself. In controlled studies, the first proper pistil clusters at the top of the main shoot appeared about 8–14 days after short days began [1][2]. Across 27 hemp cultivars the average was 13–14 days, and slow ones took three weeks [2].
Many breeders count flowering time from that point ("flower set"), not from the flip. That's why most runs seem to go about two weeks long.
Flower length itself is genetic. Indoor medical genotypes typically run 7–14 weeks of flowering [4]; equatorial types run longer.
A 13/11 schedule barely changes the clock: about 1.5 days later onset in one cultivar, none in another, with more yield [3].
The numbers
| Plant type | Weeks of flower | Weeks from flip to harvest |
|---|---|---|
| Fast indica-leaning hybrid | 7–8 | ~9–10 |
| Typical hybrid | 8–10 | ~10–12 |
| Long equatorial type | 11–16+ | ~13–18+ |
| Transition (flip to first pistil clusters) | — | 10–14 days typical; up to 3 weeks |
| Breeder's "8 weeks" | 56 days | 66–70 days |
What to do
- Log two dates: the flip, and the first 3+ pairs of pistils at the top of the main shoot.
- Add 10–14 days to any breeder's stated time.
- Plan the room on the longer figure.
- Start trichome checks about two weeks before the expected finish.
- Harvest on trichomes, mostly cloudy with some amber to taste, not the calendar.
Common mistakes
- Counting the flip as day 1 and harvesting two weeks early.
- Calling veg preflowers "flowering".
- Light leaks in the first two weeks, stalling induction.
- Judging ripeness by pistil colour alone.
Related
- Full article: The flip isn't day 1 of flower
- When should I flip my plants to flower?
- In which weeks of flower do buds grow the most?
- How do I check trichomes?
- Terms: flowering stage · flip
