# When do outdoor plants start flowering?

> Outdoor photoperiod cannabis starts flowering when days shorten past its cultivar's threshold, often around 14–14.5 hours of daylight. At 35–50° latitude that is usually late July to mid-August in the Northern Hemisphere and late January to mid-February in the Southern. Plants show pistils over the next 10–14 days. Higher latitudes cross the threshold later; near the tropics plants can flower almost any time.

- Canonical: https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.html
- Topic: Outdoor growing · Type: Numbers
- 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: Outdoor flowering time | When do outdoor plants start to bud? | Do outdoor plants flower in August? | When does outdoor cannabis flower in the southern hemisphere? | Why is my outdoor plant flowering in June?
- 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

Outdoor [photoperiod plants](https://genetixbay.com/knowledge/glossary/photoperiod.md) start flowering as days shorten past their threshold, often around 14–14.5 h of daylight. At 35–50° latitude that is usually late July to mid-August in the Northern Hemisphere, late January to mid-February in the Southern, with [pistil](https://genetixbay.com/knowledge/glossary/pistil.md) clusters showing 10–14 days later. *Supported*; exact dates vary by cultivar.

## Why

Cannabis measures night length. Once the night passes a cultivar-specific threshold, [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) switch from leaves to flower clusters [3].

Thresholds differ. Some [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) had a critical day length of 13 h 45 min to 14 h, and very dim twilight counted as light [1]. Many drug-type cultivars flower at 14 h days, and some at 14–15 h [4].

Latitude shifts the date. Days are longest at high latitude, so they fall through 14 h later: about 9 August at 40°, 23 August at 50° (sunrise to sunset, calculated).

Flowering is not instant. A transition of roughly 10–14 days follows before pistil clusters show at the [tops](https://genetixbay.com/knowledge/glossary/top-shelf.md).

Night light interferes. Stray light of about 2 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) delayed flowering in hemp [1], and as little as 0.01 µmol/m²/s in sensitive cannabis cultivars [2].

## The numbers

| Latitude | Day falls below 14.5 h | Day falls below 14 h | Typical flower onset (N / S) |
|---|---|---|---|
| 30° | Never above it | ~7 July | Early–mid July / early–mid January |
| 40° | ~25 July | ~9 August | Late July–mid August / late January–mid February |
| 45° | ~6 August | ~17 August | Early–late August / early–late February |
| 50° | ~15 August | ~23 August | Mid–late August / mid–late February |
| 55° | ~22 August | ~28 August | Late August / late February |

Southern dates: add six months. Sunrise-to-sunset values; twilight adds a little.

## What to do

1. Note when your days drop below 14.5 h and 14 h; expect flowers from then.
2. Count flowering weeks from first pistils, plus the 10–14 day transition.
3. Keep plants away from streetlights and security lights.
4. In short seasons, choose early cultivars or [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md).

## Common mistakes

- Expecting outdoor plants to flower "on [12/12](https://genetixbay.com/knowledge/glossary/12-12.md)" in September.
- Planting under a security light.
- Assuming a breeder's 8 weeks starts the day you see the first pistil.

## Related

- Full article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)
- Answers: [When to plant outdoors](https://genetixbay.com/knowledge/answers/when-to-plant-outdoors.md) · [When to harvest outdoors](https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.md) · [Why flowering needs long nights](https://genetixbay.com/knowledge/answers/why-flowering-needs-darkness.md)
- Article: [The flip isn't day 1 of flower](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.md)
- Terms: [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) · [outdoor growing](https://genetixbay.com/knowledge/glossary/outdoor-growing.md)

## Follow-up questions

**Why is my outdoor plant flowering in June?** An outdoor photoperiod cannabis plant flowering in June was usually planted out while days were still short, started from a clone taken off a flowering plant, or is an autoflower. Early-spring days at mid-latitudes are under the 13 h 45 min to 14 h threshold measured in some cultivars. Most such plants re-veg as days lengthen, losing weeks. Plant photoperiods out from late May.

**Do streetlights stop outdoor plants flowering?** Streetlights and security lights can delay or disrupt flowering in outdoor cannabis, because the plant measures uninterrupted darkness. A hemp study reported delays from stray light of about 2 µmol/m²/s, and conference work saw delays in sensitive cultivars at 0.01 µmol/m²/s. Plant away from night lighting, or shield the plant, and expect uneven flowering on the lit side.

**Can I make outdoor plants flower earlier?** Yes, you can make outdoor cannabis flower earlier with light deprivation: pull a truly lightproof cover over the plants each evening and remove it each morning to give about 12 hours of uninterrupted darkness. Photoperiod plants then flower even in midsummer, which lets growers harvest before autumn rain and mould. Covers must go on at the same time daily, and heat builds underneath.

## 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. Spitzer-Rimon B, Duchin S, Bernstein N, Kamenetsky R. 2019. Architecture and florogenesis in female Cannabis sativa plants. Frontiers in Plant Science 10:350. https://doi.org/10.3389/fpls.2019.00350
4. Peterswald TJ, Mieog JC, Azman Halimi R, et al., 2023. Moving away from 12:12; the effect of different photoperiods on biomass yield and cannabinoids in medicinal cannabis. Plants 12(5):1061. https://doi.org/10.3390/plants12051061