Crops will fall fallow in winter. Fallow crops can be harvested at any time for a reduced amount of seeds of the relevant plant.
You should change this so that you get 100% of seeds back. Losing majority of seeds is too rough and 100% certainty many people will come to forums and complain or ragequit the whole game when they realize that they have just lost most of their seeds when winter comes. Planning all your crops to fully grow before winter is a difficult task.