Short answer
Yes. A photoperiod seedling on 12/12 grows normally until it matures, then flowers straight away, giving a short plant with one main cola in roughly three months. It costs yield per plant, and suits low headroom or many small plants. Supported for the maturity step; outcomes are Grower practice.
Why
Seedlings must grow up first. Cannabis seedlings pass from a juvenile to an adult, flower-ready stage on their own, whatever the day length; in one cultivar the first single flowers formed at the 7th node [1]. Before that, long nights have little to work on.
Once mature, long nights take over. Short days make the shoot tips branch into compact inflorescences [2]. With no veg, there's little frame to build on, so the plant makes one dominant cola and a few small side buds.
Light hours cost growth. At the same intensity, 12 h gives two-thirds of the daily light of 18 h, and yield follows light [4]. Small plants also leave canopy gaps unless packed densely; higher density raises yield per area but lowers it per plant [3].
The numbers
| 12/12 from seed | Vegged photo (4 weeks) | |
|---|---|---|
| Veg time | ~3–5 weeks while it matures | 4+ weeks at 18/6, then flip |
| Shape | One main cola | Multi-top, trainable |
| Final height (typical) | Short | 1.5–3× height at flip |
| Seed to harvest | ~3 months | ~3.5–5 months |
| Yield per plant | Low | Higher |
| Best use | Low headroom, testing, many small plants | Filling a canopy with few plants |
What to do
- Use a compact cultivar and a 7–11 L (2–3 gal) pot.
- Run 12/12 (or 13/11) from sprouting, at seedling intensity first.
- Keep the dark period truly dark from day one.
- Grow several plants per square metre to fill the canopy, within legal limits.
- Harvest by trichomes, not the calendar.
Common mistakes
- Expecting flowers in week 1.
- Using a stretchy, long-flowering cultivar.
- Leaving one tiny plant alone under a big light.
- Light leaks, which push the plant back towards veg.
Related
- Full article: Photoperiod and light leaks
- Answers: autos and photos in one tent · when to flip · why flowering needs long nights
- Article: Sea of green
- Terms: 12/12 · veg time
