Growing Season: Tromsø
Tromsø, Troms, Norway
Growing season
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
8 Apr
Daylight
10+ h
14+ h
10+ h
8 Mar
5 Apr
8 Sep
5 Oct
211 days
Frost-free
10% frost-free
10 May
8 Oct
90% frost risk
151 days
Effective
10 May
5 Oct
148 days
The growing season in Tromsø is approximately 148 days and is limited by both frost and daylight.
Last spring frost
The last spring frost normally occurs on 10 May in Tromsø. At the earliest, the last frost is over around 30 Apr and at the latest around 23 May.
| Frost-free probabilityFrost-free prob. | Date | Grower's risk level | Explanation |
|---|---|---|---|
| 10% | 30 Apr | High risk | Frost 9 out of 10 years after this date |
| 25% | 5 May | Frost 3 out of 4 years after this date | |
| 50% | 10 May | Normal risk | Frost every other year after this date |
| 75% | 18 May | Frost 1 out of 4 years after this date | |
| 90% | 23 May | Low risk | Frost 1 out of 10 years after this date |
Growing is often planned around the date when there is a 50% probability that the last spring frost has occurred. In Tromsø that is 10 May. If you want lower frost risk, choose 75% or 90%, i.e. a later date.
First autumn frost
The first autumn frost normally occurs on 8 Oct in Tromsø. At the earliest, frost can arrive around 23 Sep and at the latest around 18 Oct.
| Frost probabilityFrost prob. | Date | Grower's risk level | Explanation |
|---|---|---|---|
| 10% | 23 Sep | Low risk | Frost 1 out of 10 years on or before this date |
| 25% | 2 Oct | Frost 1 out of 4 years on or before this date | |
| 50% | 8 Oct | Normal risk | Frost every other year on or before this date |
| 75% | 13 Oct | Frost 3 out of 4 years on or before this date | |
| 90% | 18 Oct | High risk | Frost 9 out of 10 years on or before this date |
Growing is often planned around the date when there is a 50% probability that the first autumn frost has occurred. In Tromsø that is 8 Oct. If you want lower frost risk, choose 10% or 25%, i.e. an earlier date.
Daylight & Persephone Period
Plants need at least 10 hours of daylight to grow actively. The period with under 10 h is called the Persephone period.
| From | To | Number of days | |
|---|---|---|---|
| Daylight over 10 h | 8 Mar | 5 Oct | 211 |
| Persephone period | 6 Oct | 7 Mar | 154 |
Plan the year's last sowing of cold-hardy plants in Tromsø so they are approximately 75% mature by 6 Oct when daylight drops below 10 h and growth starts to slow.
Daylight periods
Long-day plants like lettuce, spinach and coriander bolt when daylight gets too long. Plan sowing and harvest during periods when daylight is shorter (10-14 h). Early spring or late summer sowing gives the best results.
| Season | Light | Period | Days | Advice |
|---|---|---|---|---|
| Shorter daylight | 10-14 h | 8 Mar – 4 Apr | 28 | Grow long-day plants like spinach, lettuce and coriander. |
| Longer daylight | 14+ h | 5 Apr – 7 Sep | 156 | High risk of bolting |
| Shorter daylight | 10-14 h | 8 Sep – 5 Oct | 28 | Grow long-day plants |