# Can I grow autoflowers and photoperiods in the same tent?

> You can grow autoflowers and photoperiods in the same tent, but one schedule must lose. On 18/6 to 20/4 the autos thrive and the photos stay in veg; on 12/12 the photos flower and the autos lose about a third of their daily light, and yield with it. The best plan is to veg photos alongside autos, then flip after the autos are harvested, or use two spaces.

- Canonical: https://genetixbay.com/knowledge/answers/autos-and-photos-in-one-tent.html
- Topic: Basics · Type: How-to
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Full article: [Photoperiod vs autoflower, and how autoflowering is inherited](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md)
- Also asked as: Mixing autos and photos | Auto and photo together in one tent | Autos in a 12/12 tent | Can I grow autos on 12/12?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

Yes, but only one of them gets its ideal schedule. On [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) or 20/4, [autos](https://genetixbay.com/knowledge/glossary/autoflower.md) thrive and [photos](https://genetixbay.com/knowledge/glossary/photoperiod.md) stay in veg. On [12/12](https://genetixbay.com/knowledge/glossary/12-12.md), 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](https://genetixbay.com/knowledge/glossary/recessive.md) auto [allele](https://genetixbay.com/knowledge/glossary/allele.md) 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](https://genetixbay.com/knowledge/glossary/dli.md) at 600 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) |
|---|---|---|---|
| 20/4 | Ideal | Stay in veg | 43.2 mol/m²/day |
| 18/6 | Ideal | Stay in veg | 38.9 mol/m²/day |
| [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) | 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

1. Start autos and photos together on 18/6 or 20/4.
2. Train the photos low ([LST](https://genetixbay.com/knowledge/glossary/lst.md)) while the autos run their course.
3. Harvest the autos at 9–14 weeks.
4. Flip the photos to 12/12 or 13/11 at about half the height you can fit.
5. If you must flower both at once, run 12/12 or 13/11 and accept smaller autos.
6. 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](https://genetixbay.com/knowledge/basics/photoperiod-vs-autoflower.md)
- Answers: [12/12 from seed](https://genetixbay.com/knowledge/answers/12-12-from-seed.md) · [when to flip](https://genetixbay.com/knowledge/answers/when-to-flip-to-flower.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md)
- Article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)
- Terms: [autoflower](https://genetixbay.com/knowledge/glossary/autoflower.md) · [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md)

## Follow-up questions

**Can I grow autos on 12/12?** Yes, autoflowers will still flower on 12/12, because they flower by age rather than night length. But it wastes their potential: on 12/12 an auto gets much less daily light than on 18–20 hours, which give about 1.5–1.7 times the light at the same intensity. With a fixed countdown, the auto can't make up the lost growth later.

**What is the best way to mix autos and photos?** The best way to mix autos and photos in one tent is to start them together on 18/6 or 20/4. The autos flower and finish on their own clock while the photoperiods veg and get trained. Once the autos are harvested at about 9–14 weeks, flip the photos to 12/12. Plan headroom: the photos will be big by then.

**Will an autoflower mess up my photoperiods?** An autoflower won't change your photoperiods' flowering, because light schedule, not neighbouring plants, sets when photos flower. The real risks are a mismatched schedule, uneven canopy heights under one light, and pollen if either plant is male or hermaphrodite. Opening the tent in the dark period to tend autos would be a light leak for flowering photos.

## Sources

1. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680
2. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020
3. Zhang M, Anderson SL, Brym ZT, Pearson BJ. 2021. Photoperiodic flowering response of essential oil, grain, and fiber hemp (Cannabis sativa L.) cultivars. Frontiers in Plant Science 12:694153. https://doi.org/10.3389/fpls.2021.694153