# Why is my plant growing single-finger leaves?

> Single-finger, rounded leaves on a cannabis plant usually mean it is revegging: switching from flowering back to vegetative growth because its nights became too short or were broken by light. Common causes are light leaks in flower, timer faults, outdoor plants put out under short spring days, and clones cut from flowering plants. Keep the dark period truly dark, below about 0.01–2 µmol/m²/s.

- Canonical: https://genetixbay.com/knowledge/answers/single-finger-leaves-reveg.html
- Topic: Diagnosis · Type: Troubleshooting
- Evidence: Supported · Status: Draft: awaiting expert review
- Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)
- Also asked as: Is my plant revegging? | Round, single-blade leaves on my plant | Revegging plant in flower | Smooth leaves with no serrations
- 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

Single-finger, rounded leaves usually mean a cannabis plant is [revegging](https://genetixbay.com/knowledge/glossary/re-veg.md): going from flower back to vegetative growth because its nights got too short or were broken by light. The common causes are [light leaks](https://genetixbay.com/knowledge/glossary/light-leak.md) or timer faults in flower, outdoor plants set out under short spring days, and clones cut from flowering plants. *Supported*.

## Why

[Photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) cannabis reads the night. Flowering starts once the uninterrupted dark is long enough, and it stalls or reverses when nights shorten or are broken [1].

Very little light can break a night. A [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) study reported flowering delays from stray light at about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) [1], and a 2024 conference report saw delays in the most sensitive cannabis cultivars at 0.01 µmol/m²/s [2].

A mid-night pulse of light is used on purpose. Growers keep [mother plants](https://genetixbay.com/knowledge/glossary/mother-plant.md) vegetative on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md) with a 1-hour night break [3], which shows how well a short interruption works. An accidental leak does the same thing to a flowering plant.

Revegging leaves look distinctive. New growth comes in as single blades or 3-finger leaves with smooth or rounded edges, sometimes poking out of the buds.

## The numbers

| Situation | Threshold |
|---|---|
| Dark-period stray light | As near 0 as you can measure; below 0.01–2 µmol/m²/s [1][2] |
| Eye test | Nothing visible after 5 minutes with eyes adjusted |
| Flower schedule | 12/12 or [13/11](https://genetixbay.com/knowledge/glossary/13-11.md) (house-endorsed), uninterrupted dark |
| Reveg recovery | About 2–4 weeks before normal leaves return (grower practice) |

## What to do

1. Sit in the dark room for 5 minutes. Tape over indicator [LEDs](https://genetixbay.com/knowledge/glossary/led.md), zipper ends and duct ports.
2. Check that the timer and controller logs match the schedule, especially after a power cut.
3. Make sure no light reaches the room from a veg area or a door gap.
4. Outdoors, plant out photoperiod cultivars once the days are long, or add light in early spring.
5. Take clones from vegetative mothers, not flowering plants.
6. Once you've fixed the cause, give the plant time. Don't add stress on top.

## Common mistakes

- Opening the tent during the dark period.
- Trusting a mechanical timer that drifts.
- Putting photoperiod plants outside in early spring.
- Mistaking a [seedling](https://genetixbay.com/knowledge/glossary/seedling.md)'s first single-blade leaves for reveg.

## Related

- Full article: [Photoperiod and light leaks](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)
- Answers: [how to reveg a plant](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.md) · [lights stayed on in flower](https://genetixbay.com/knowledge/answers/lights-stayed-on-during-flower.md) · [opening the tent at night](https://genetixbay.com/knowledge/answers/opening-tent-during-dark-period.md) · [when to plant outdoors](https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.md)
- Terms: [re-veg](https://genetixbay.com/knowledge/glossary/re-veg.md) · [light leak](https://genetixbay.com/knowledge/glossary/light-leak.md)

## Follow-up questions

**How long does revegging take?** Revegging a cannabis plant usually takes about 2–4 weeks before normal multi-finger leaves return, according to grower practice, and it can be slower on a plant cut from late flower. Expect odd single-blade and smooth-edged leaves first. Keep it on 18/6 or longer days in veg conditions, and leave plenty of green growth and bud sites when harvesting a plant you plan to reveg.

**Why are my outdoor plants growing single-blade leaves?** Outdoor cannabis planted early in spring often grows single-blade leaves because short spring days start flowering, and then lengthening days push it back into veg, a reveg. Plant photoperiod cultivars out after days are long enough to keep them vegetative, or give them extra light indoors first. Expect a 2–4 week stall while they recover.

**Are single-finger leaves normal on clones?** Single-finger leaves are normal on clones cut from a flowering or recently flowering mother, because the cutting has to reveg before it grows normally. On clones from a vegetative mother on 18/6 or longer, they shouldn't appear. Take cuttings from vegetative mothers for faster rooting and growth, and expect a slow start from flowering cuts.

## Sources

1. 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
2. Eckels M, Bugbee B, 2024. Night light pollution delays flowering in soybean and cannabis (ASHS 2024 conference abstract). https://ashs2024.sched.com/event/1dtbo/ce-4-night-light-pollution-delays-flowering-in-soybean-and-cannabis
3. Examining the night break method in Cannabis sativa horticulture: vegetative daily light integral affects yield of extractable biomass, 2025. Plants 14(19):3095. https://pmc.ncbi.nlm.nih.gov/articles/PMC12525983/