The bilberry flowers between May and June. Successful flowering requires favourable weather conditions and a sufficient number of pollinators. The main pollinators of lingonberry are bumblebees and insects.
In summer, an abundance of light, warmth and a suitable amount of moisture ripen the wild Arctic bilberries. It usually takes 8–10 weeks for a bilberry to develop from a flower into a ripe berry. In mid-summer, there are 19 hours of daylight in the southern parts of the Nordic countries, and in the northern Arctic Circle region the sun does not set at all. According to studies, this abundance of light promotes the formation of anthocyanin compounds. Due to the northern location, Arctic bilberries that grow wild in the forests form extremely high levels of anthocyanin and polyphenol.
In the southern parts of the Nordic countries, the bilberry usually ripens in mid-July, while in the northern parts it ripens in late July and early August. Weather conditions in early summer can affect the ripening time greatly.
The berry is spherical with a diameter of 6–8 mm. It is either dark blue and waxy or black and shiny, and dark blue on the inside. The berry can be identified by the distinctive pattern on its bottom.
It has been estimated that only Finnish forests and peatlands produce an average of 184 million kg of bilberries annually (Turtiainen et al. 2007). In 1997-2018, the range of variation in total yields was from 92 to 312 million kg (Turtiainen 2021).
Over 15 million kilograms of bilberries are picked for households in Finland. This number however makes up less than 10 per cent of the bilberry’s natural harvest, meaning that lots of this valuable berry is left in the forest.