Spring

In spring, the mean daily temperature rises from 0°C to 10°C. Spring begins in early April in Åland and the southwestern archipelago and later in April elsewhere, except for northernmost Lapland, where it does not begin until early May.

Thus, spring begins a month earlier in the south than in the north. Its duration ranges from 45 to 65 days, being longest in the islands and coastal regions, because of the coolness of the sea. Once the mean daily temperature exceeds 5°C, the thermal growing season is considered to have begun. This take place about one month after the beginning of spring: at the end of April in southern Finland and at the end of May in northernmost Lapland.

For the real growing season to begin the snow must melt; this depends on the amount of snow, elevation and the position of the region relative to the sea. Open areas lose their snow cover within two to three weeks of the beginning of spring, whereas on average the snow in the forest smelts about two weeks later. The lakes usually become ice-free soon after the growing season begins in April in southwestern Finland, in May in the interior, and in June in Lapland.