Short answer
Yes, but only one of them gets its ideal schedule. On 18/6 or 20/4, autos thrive and photos stay in veg. On 12/12, photos flower and autos lose about a third of their daily light. The usual fix: grow them together under long days and flip the photos once the autos are harvested. Grower practice.
Why
Autos ignore the clock. Plants with two copies of the recessive auto allele flower by age, even under long days [1]. They don't need 12/12.
Photos read the night. Photoperiod cannabis stays vegetative until the uninterrupted night passes its critical length, and even dim stray light can delay flowering [3].
Light hours are yield for an auto. At the same intensity, 18–20 h of light gives 1.5–1.7 times the daily light of 12 h, and yield rose with light in a controlled trial [2]. An auto on 12/12 flowers on schedule, but smaller.
The numbers
| Schedule | Autos | Photos | DLI at 600 µmol/m²/s |
|---|---|---|---|
| 20/4 | Ideal | Stay in veg | 43.2 mol/m²/day |
| 18/6 | Ideal | Stay in veg | 38.9 mol/m²/day |
| 13/11 | Lose light | Flower (endorsed) | 28.1 mol/m²/day |
| 12/12 | Lose ~a third of light | Flower | 25.9 mol/m²/day |
DLI = PPFD × hours × 0.0036.
What to do
- Start autos and photos together on 18/6 or 20/4.
- Train the photos low (LST) while the autos run their course.
- Harvest the autos at 9–14 weeks.
- Flip the photos to 12/12 or 13/11 at about half the height you can fit.
- If you must flower both at once, run 12/12 or 13/11 and accept smaller autos.
- With two spaces, give each its own schedule.
Common mistakes
- Putting a new auto into a flowering tent and expecting a full-size plant.
- Running 18/6 and wondering why the photos never flower.
- Opening the tent during the dark period to tend autos.
- Hanging one light for two very different canopy heights.
Related
- Full article: Photoperiod vs autoflower
- Answers: 12/12 from seed · when to flip · opening the tent at night
- Article: Photoperiod and light leaks
- Terms: autoflower · photoperiod
