Quoted By:
No because not all plants with leaves even do that, it's an adaptation that temperate plants developed in order to survive the harsher winters compared to more tropical climates
Plants in tropical regions simply die if they are exposed to climates that are more dry or have darker winters. But since most Grass Pokemon don't appear to be fueled solely by photosynthesis and air moisture it wouldn't really make sense for them to go dormant in the winter
In fact you can bring a Leafeon to Mt. Coronet or in both autumn and winter in Unova and it seems to have no effect so I'm not sure why this is even a question for you
