It kinda depends on what you want. Germany has warm summers and cold winters with the north being more wet and less cold in winter. The summer in the northern parts would generally be cooler and with more rain than in the south.

Winter season would be December till February. It should be reasonably warm from May until late September. Don't rely on it though.

Summers can be lousy cold and winters without snow are not that unusual. The only place where you can rely on snow is the higher altitudes in the mountainous parts.