# How do I grow outdoors in a short northern season?

> To grow outdoors in a short northern season (roughly 50° latitude and above, with frost by late September or October), pick plants that finish by late September: autoflowers, or early-finishing photoperiod lines. Start indoors 3–6 weeks before last frost, harden off, plant out in early June, and use a greenhouse, hoop cover or light deprivation to dodge autumn rain. Check local rules first.

- Canonical: https://genetixbay.com/knowledge/answers/outdoor-short-season.html
- Topic: Outdoor growing · Type: How-to
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md)
- Also asked as: Short-season outdoor growing | Growing cannabis outdoors in a cold climate | Outdoor grow in Canada or northern Europe | What finishes before frost up north? | Outdoor growing at 50 degrees latitude
- 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

Grow plants that finish by late September: [autoflowers](https://genetixbay.com/knowledge/glossary/autoflower.md), or [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) lines bred to flower early. Start indoors, plant out after the last frost (usually early June at 50° and above), and keep rain off the buds in autumn. *Grower practice*. [Home growing](https://genetixbay.com/knowledge/glossary/home-grow.md) outdoors is legal only in some places, so check local rules first.

## Why

Long northern days delay flowering. Cannabis flowers when nights pass a cultivar's threshold, often near 14 h of day [1]. At 50° latitude days stay above 14 h until about 23 August, against 9 August at 40° (calculated, sunrise to sunset). Add the 10–14 day transition and an 8–10 week flower, and a typical cultivar finishes in late October.

Genetics can move the date. Breeding work has mapped *Autoflower1* and an early-flowering [locus](https://genetixbay.com/knowledge/glossary/locus.md), *Early1* [2]. Autos ignore day length; early photoperiod lines simply start and finish sooner.

A head start indoors buys weeks. [Seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) started indoors and hardened off go out at a useful size the day frost risk passes [3].

Autumn wet is the real threat. Gray mould thrives in cool, wet weather on dense buds [4], and northern Septembers deliver both.

## The numbers

| Approach | Plant out (N / S) | Harvest (N / S) |
|---|---|---|
| Autoflower, sown direct | Early June / early December | Mid-August–early September / mid-February–early March |
| Early photoperiod line | Early June / early December | Mid–late September / mid–late March |
| Typical photoperiod | Early June / early December | Late October or later / late April or later |
| [Light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) (~12 h dark from early July) | Early June / early December | Late August–September / late February–March |

## What to do

1. Choose autos or proven early-finishing photoperiods; avoid late tropical lines.
2. Start photoperiods indoors 3–6 weeks before last frost on long days.
3. [Harden off](https://genetixbay.com/knowledge/glossary/hardening-off.md) for 7–14 days.
4. Plant out after the last frost, in the sunniest, best-drained spot.
5. Use containers, a greenhouse or a hoop cover to warm roots and keep rain off.
6. Consider light deprivation for photoperiods.
7. Watch forecasts from September and harvest ripe plants ahead of long rain or a hard freeze.

## Common mistakes

- Growing a 12-week cultivar where frost arrives in early October.
- Planting out too early and losing plants to a late frost.
- Closing a greenhouse up tight and breeding mould.
- Skipping the local-rules check.

## Related

- Full article: [The cannabis life cycle, stage by stage](https://genetixbay.com/knowledge/basics/life-cycle.md)
- Answers: [Autoflowers outdoors](https://genetixbay.com/knowledge/answers/autoflowers-outdoors.md) · [When outdoor plants flower](https://genetixbay.com/knowledge/answers/when-do-outdoor-plants-flower.md) · [When to harvest outdoors](https://genetixbay.com/knowledge/answers/when-to-harvest-outdoors.md)
- Terms: [light deprivation](https://genetixbay.com/knowledge/glossary/light-deprivation.md) · [greenhouse growing](https://genetixbay.com/knowledge/glossary/greenhouse-growing.md)

## Follow-up questions

**Why do outdoor plants finish late up north?** Outdoor photoperiod cannabis finishes late at high latitude because long summer days delay flowering. At 50° latitude, days stay above 14 hours until about late August, against early August at 40°, so a cultivar needing 8–10 weeks plus a 10–14 day transition finishes in late October, after frost in many northern areas. Early-flowering genetics or light deprivation fix it.

**Are autoflowers best for short northern seasons?** Autoflowers are often the safest choice for short northern seasons, because they flower by age and finish about 9–14 weeks from seed whatever the day length. Sown in early June, after the last frost, they finish from mid-August to early September, ahead of autumn rain and frost. Sow straight into the final container and use LST rather than topping, because any setback costs yield.

**Does a greenhouse help in a short season?** A greenhouse or plastic hoop cover helps a short-season cannabis grow by keeping rain off buds, holding warmth on cold nights and letting you plant out a few weeks earlier. Ventilate it well, because heat and humidity build fast inside. Add light-deprivation covers to force photoperiods to flower in midsummer and harvest before autumn weather. Check local rules on greenhouse growing too.

## 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. 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
3. University of Minnesota Extension. Starting seeds indoors (transplanting seedlings, hardening). https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors
4. PNW Plant Disease Management Handbook. Hemp (Cannabis sativa) - Gray Mold. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-gray-mold-botrytis-bud-blight-stem-canker