After the upload, the BBox (EPSG:3857) is automatically displayed. Attention: The Radolan data is analyzed on the basis of the bounding box, not the polygons.
Info: season range dates
Spring: 1.3. - 31.5.
Summer: 1.6. - 31.8.
Autumn: 1.9. - 30.11.
Winter: 1.12. - 28.2.
So Startdates should be 1.3., 1.6., 1.9., 1.12. and Enddates 31.5., 31.8., 30.11., 28.2.