- If you’re unsure, run 12/12. It’s the most repeatable “works on most strains” baseline.
- 11/13 is a targeted lever: a longer, uninterrupted dark period can help some long‑flowering / haze‑leaning genetics commit and finish cleaner.
- The cost is real: if light intensity stays the same, 11/13 delivers about 8.3% less daily light than 12/12. That can mean less yield or slower bulking.
- Don’t change schedule + intensity + feed at once. One variable. Small steps. Watch the plant.
What changes between 11/13 and 12/12
12/12 means 12 hours of light, 12 hours of darkness. 11/13 means 11 hours of light, 13 hours of darkness.
For photoperiod cannabis, the continuous dark period is part of the flowering signal. More uninterrupted darkness can push certain genetics to behave more “decisively” in late flower. But less light time also means fewer total photons per day (unless you compensate by raising intensity).
The DLI trade (the part people ignore)
- Going from 12 hours → 11 hours is 11/12 = 0.9167 (about −8.3% daily light).
- That small‑sounding cut stacks up across weeks.
In plant lighting, growers often describe this as Daily Light Integral (DLI): the total usable light delivered per day.
Translation: 11/13 can improve finishing behavior for some genetics, but it’s not “free.” If you’re already light‑limited, cutting hours is usually the wrong direction.
What research suggests (and what it doesn’t)
- Controlled studies show that a 12‑hour flowering photoperiod may not maximize yield for all cultivars, and longer photoperiods can increase yield in some cases—often because of higher daily light exposure.
- Other research notes that photoperiod can affect days to flower (e.g., longer photoperiods can delay flowering in some contexts), which is why “more hours” isn’t automatically better for every goal.
- Bottom line: genetics decide the response. A schedule change can improve one cultivar and do nothing (or worse) on another.
When 12/12 wins
12/12 is the industry default because it works across the widest range of genetics with the least drama.
- You want the safest flip into flower.
- You’re dialing in a new strain and need a clean baseline.
- Your environment control isn’t consistent yet (temp / RH swings, weak airflow, unstable VPD).
- You want predictable scheduling for perpetual systems.
When 11/13 can win
11/13 is not “better.” It’s a tool for specific problems—most often in late flower.
- Long‑flowering / haze‑leaning genetics that drag their feet under 12/12.
- Plants that keep throwing fresh pistils and feel like they “won’t commit.”
- Endless stretch / “staying in transition” behavior that doesn’t match your expectations.
- You want a stronger dark‑period signal without adding more equipment or complexity.
When 11/13 is the wrong move
- You’re light‑limited (weak fixture, too much canopy shading, low PPFD at the bud sites).
- Your “problem” is actually environment (too hot, too humid, poor airflow) or harvest timing—not the schedule.
- You change multiple variables at once and then blame the schedule when the plant stalls.
How to switch without stalling
- Pick one variable. Don’t change schedule + intensity + nutrients at the same time.
- Make a small step. Example: reduce the light window by 15 minutes every 2–3 days until you reach 11 hours.
- Hold and observe. Give the plant 3–5 days to show you a direction (stretch rate, pistil behavior, leaf posture).
- Don’t chase day‑to‑day noise. Look for consistent trends over a week.
What to watch after you change it
- Good signs: tighter behavior, fewer “fresh” white pistils late, more stable ripening pace.
- Bad signs: obvious stall (no swelling), stress stacking (curling, clawing, bleaching), or the plant looking “sleepy” during lights‑on.
- If it backfires: return to 12/12 and stabilize environment first. Don’t keep twisting knobs.
FAQ
Is 11/13 more potent?
Not inherently. Potency is mostly genetics + environment + harvest timing. 11/13 can change behavior; it doesn’t magically add THC.
Will 11/13 reduce yield?
It can. If light intensity stays the same, you’re delivering ~8.3% less daily light than 12/12. The “win” is a cleaner finish for certain genetics, not free yield.
Should I start flower on 11/13 from day one?
Usually no. Establish flower first (often on 12/12), then adjust if the strain benefits—especially late flower.
When is the best time to try 11/13?
Most people test it after the plant is clearly in flower (often week 3+) or as a late‑flower lever (final 2–4 weeks) for long‑flowering genetics.
Can I compensate by increasing light intensity?
Sometimes. But higher intensity can increase heat and stress. If you compensate, do it slowly and watch leaf posture and bud‑site bleaching.
Is 11/13 the same as “10/14” or other short schedules?
They’re the same idea (more darkness), just more extreme. The shorter you go, the more you cut daily light—so the yield tradeoff gets bigger.
What’s the safest approach for beginners?
Run 12/12, keep your environment stable, and learn what “normal” looks like for your genetics before making schedule experiments.
Does a longer dark period automatically make plants finish faster?
No. Some cultivars respond, others don’t. If the issue is environment or harvest timing, 11/13 won’t save you.
Will 11/13 improve terpenes?
Not by itself. Terpene retention is mostly about avoiding heat/light stress during the grow and running a clean dry/cure after harvest.
What if I try it and the plant stalls?
Go back to 12/12, stabilize, and stop changing multiple variables. A stall usually means stress stacking, not “wrong schedule.”
Sources
- Ahrens et al. (2024) — 12 h vs. 14 h flowering photoperiod in high‑THC cultivars (Plants, MDPI)
- Ahrens et al. (2024) — Longer photoperiod increases indoor cannabis yield (open‑access, PMC)
- Peterswald et al. (2023) — Review/analysis on photoperiod effects, flowering time, and yield (open‑access, PMC)
- Grover et al. (2025) — “Night break” photoperiod method study in cannabis (open‑access, PMC)
- Llewellyn et al. (2022) — Indoor cannabis yield increases with light intensity (Frontiers in Plant Science)
Next steps
- 14/10 light cycle explained — When extra light helps and when it creates problems.
- Seed to harvest haze protocol — How to ramp and finish long-flowering strains cleanly.
- Strain-aware growing — Match schedule to genetics instead of forcing a template.
- Late-flower stall (not nutrients) — Diagnose slowdowns without chasing deficiencies.