According to observations of naturalists and beekeepers.
Where are you?
This plant is present in at least 13 states/provinces in this country.
Blueberry willow's two varieties differ significantly in growth form. Low blueberry willow is a much-branched, low-growing, and often prostrate shrub typically between 8 and 24 inches (20-60 cm) tall. Tall blueberry willow is an erect shrub often 6 to 8 feet (2.0-2.5 m) tall but is occasionally taller. Both varieties have relatively small, simple, alternate, deciduous leaves. Male and female flowers occur on separate plants in 3/4- to 2-inch-long (1.5-5 cm) erect or ascending catkins. The fruit is a two-valved capsule.
In Alaska, low blueberry willow catkins appear after the leaves have begun to develop. Seeds are dispersed during the growing season, about mid-June.
In Alaska, tall blueberry willow catkins appear after the leaves have begun to develop. Flowering is in early to mid-June, seeds mature in late June to mid-July, and catkins fall in late July.