On Florges, how would the move "Flower Shield" work?
The user raises the Defense stat of all Grass-type Pokémon in battle with a mysterious power.
Does this mean that it would affect opponents as well?
Yes, it would raise the Defence of both your Pokemon and your opponent's Pokemon.
Yes, it means all grass Pokémon in battle will be affected. It's just one of those moves that you have to use strategy with.(In a grand master voice):"Use wisely, my friend."
Hope I helped!