Precisely where in the garden is it planted? In shade, near other large trees and shrubs? Full sun or sun and shade? A photograph of it and its immediate surroundings would be useful.

It has to have grown a little, or it wouldn't have leaves on it. The first thing I would try is to spread some compost on the soil around it, maybe about 2-3 cm deep, and as wide as the bush plus 1 meter, for root growth. That will hopefully improve the soil conditions. Also check the soil pH: if it is less than 6.5, you may want to add some lime. If that doesn't help by next summer, dig a test hole about 1/2 meter from the edge of the bush, and about a meter deep, and see what's down there. If there is very shallow soil--less than 2/3 m deep--you may need to find a different spot for it. Heavy winds will also stunt its growth. Good luck!