alot of winter plants are available for growing real world wise in the winter. Most are greens related to spinich, brocoli, and cabbage. Winter wise as far as fruit goes would be holly, and mistletoe.
Mistle toe could be interesting as a winter forage in hich you shake oak and maple trees and have a chance of it falling (similar to seeds). Could be a cute thing to get a kiss from a boyfriend, girlfriend or krobus. Maybe incorperate a heart event between marley and lewis. Jas and vincent could be funny. Vincent is in the forest playing with Jas. he pokes a tree and a banch falls he walks up to jas saying whats this. She blushes and gives him a little peck on the cheek and he runs off screaming like he just caught cooties.
Now there are some other items that grow in the winter however the game has a pretty decent fungus list without over complicating things