Winter is the fourth season players play through. It's followed by spring and preceded by fall. Winter is one of the hardest seasons, because all of the bushes and grass dies out. This makes fiber and hay virtually impossible to obtain (Although fiber in Mines grows normally). However, some of the most valuable items obtainable appear only in this season.
An effective way to obtain yam and root is to go to a long, open strip of land (preferably outside the farm so you won't have to clean up) and till with a hoe horizontally until a tile yields something. Then till upwards on that same tile, and all of the tiles should contain something. If you till a different tile horizontally, it will render the item that was found of the last "column" nonexistent. [Note: This method may not work anymore.]
Fish
There are a variety of fish which can only be caught during specific seasons. Listed below are seasonal fish catchable during Winter.
Fish which can be caught year-round are not listed below. Fish without information in "Used in" can also be used for recipes with the tag "any fish".