Regarding Northsky not fruiting -- all the sources I have checked say it is not self-fertile, or only poorly so. You need a pollinator. Northland, Northcountry, and Northblue would do the trick (that is, assuming that bees are visiting your plant).

Donna

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Tracey said:
I have a miniature blueberry bush - Vaccinium corymbosum 'Northsky' - on
our balcony. I have had it around three/four years and it seems to
flourish, and each year produces a mass of flowers, but it never fruits. It
is supposed to be self fertile, so not having another plant isn't the
problem here.