Growing cannabis outdoors in the northern half of Europe is challenging due to relatively low temperatures and a shorter growing season. However, with careful planning and suitable strains, good harvests can still be achieved.
This calendar provides precise guidelines on average sunlight duration and seasonal temperatures in reference cities such as London, Paris, and Bern, as well as Reykjavik for more extreme climates.
Fundamental Principles to Know Before Starting
- Growing Season Duration: In Northern Europe, outdoor growing typically starts in May and ends between September and October.
- Climate Types: Atlantic climates tend to be wetter, while continental climates experience more significant temperature variations.
- Indoor Germination and Growth: It is recommended to start cultivation under artificial light before moving plants outdoors to extend the vegetative phase.
- Light Optimization: An 18-hour light photoperiod per day helps maintain active growth before transitioning to natural outdoor flowering.
- Strain Selection: Fast-flowering strains (Indica or autoflowering) are particularly well-suited to northern climates.
Month-by-Month Growing Calendar
January
- Average Day Length: 8h18 – 9h20
- Average Temperature: 2°C – 8°C
- Reykjavik: 4h20 – 6h47 of sunlight, temperature between -2°C and 2°C
Cold limits all outdoor activity. This is the ideal time to prepare for the growing season by cleaning and setting up the indoor cultivation space. Growers can also use this period to select their strains and enrich the soil with organic amendments such as bat guano or worm humus.
February
- Average Day Length: 9h21 – 10h50
- Average Temperature: 2°C – 9°C
- Reykjavik: 6h53 – 9h49 of sunlight, temperature between -2°C and 2°C
Winter conditions persist. In milder areas, seed germination can begin under low-energy lamps (200W), maintaining a temperature of 20-26°C under light. By the end of the month, it is advisable to prepare outdoor soil by tilling and adding organic fertilizers.
March
- Average Day Length: 10h53 – 12h40
- Average Temperature: 4°C – 12°C
- Reykjavik: 9h55 – 13h11 of sunlight, temperature between -1°C and 3°C
Days are getting longer, allowing for seed germination and early plant growth under artificial light. Late March is an excellent time for taking cuttings if a mother plant is available.
April
- Average Day Length: 12h45 – 14h25
- Average Temperature: 5°C – 16°C
- Reykjavik: 13h18 – 16h30 of sunlight, temperature between 1°C and 6°C
Spring is well established, making it possible to gradually move young plants outdoors. It is advisable to monitor nighttime temperatures and shelter the plants if necessary.
May
- Average Day Length: 14h28 – 15h48
- Average Temperature: 8°C – 19°C
- Reykjavik: 16h36 – 19h49 of sunlight, temperature between 4°C and 9°C
The outdoor growing season officially begins. Plants can be placed in the ground, provided there is no longer a risk of frost. In northern regions, autoflowering strains are recommended to compensate for the short summer season.
June
- Average Day Length: 15h50 – 16h09
- Average Temperature: 11°C – 22°C
- Reykjavik: 19h54 – 21h01 of sunlight, temperature between 7°C and 12°C
The summer solstice (June 21) marks the longest day of the year. Plants grow rapidly thanks to maximum sunlight exposure. Regular watering and nutrient supply are essential for optimal development.
July
- Average Day Length: 16h08 – 15h15
- Average Temperature: 13°C – 25°C
- Reykjavik: 20h57 – 18h19 of sunlight, temperature between 8°C and 13°C
The flowering phase begins for some feminized strains. It is crucial to identify and remove male plants in regular crops to prevent pollination of females.
August
- Average Day Length: 15h12 – 13h31
- Average Temperature: 13°C – 25°C
- Reykjavik: 18h12 – 14h55 of sunlight, temperature between 8°C and 13°C
Autoflowering strains sown in May are now ready for harvest. Increased vigilance is necessary to prevent mold formation due to humidity.
September
- Average Day Length: 13h34 – 11h52
- Average Temperature: 11°C – 22°C
- Reykjavik: 14h49 – 11h41 of sunlight, temperature between 5°C and 10°C
Feminized plants enter full bloom. Installing stakes to support flower-laden branches is recommended, as well as providing shelter in case of heavy rain.
October
- Average Day Length: 11h48 – 10h04
- Average Temperature: 9°C – 18°C
- Reykjavik: 11h36 – 8h21 of sunlight, temperature between 2°C and 6°C
Harvest time begins for most feminized strains. Slow, controlled drying in a dark, well-ventilated area ensures a higher-quality final product.
November
- Average Day Length: 10h01 – 8h40
- Average Temperature: 5°C – 11°C
- Reykjavik: 8h15 – 5h18 of sunlight, temperature between 0°C and 3°C
The last Sativa plants finish flowering. Now is the time to start the drying and storage process for the harvested cannabis.
December
- Average Day Length: 8h39 – 8h17
- Average Temperature: 3°C – 8°C
- Reykjavik: 4h of sunlight, temperature between -2°C and 2°C
The growing season is over. It’s time to assess the results and prepare for the next year by adjusting techniques and strain choices based on the past season’s outcomes.
