Northern nature dictates the harsh terms
Finland is the only Member State of the European Union where the ground freezes every winter throughout the country. In Pirkanmaa, the ground frost does not thaw until after mid-April, which means that even in warm weather it is not possible to begin work in the fields until May. The ground frost can even run deeper in southern Finland than it does in the north, since in the north the thicker layer of snow protects the ground against freezing.
Source: Finnish Environment Institute