It’s hard to anticipate the movements of enemies to use seeds effectively. I always throw a seed where I believe the enemy will go next. Throwing a seed at the tile where the enemy is now will not activate the effect and will allow them to safely move on. If you throw it where they will move to next turn, when they move into that tile, the seed effect will activate.
My favorite offensive uses for seeds are poison (sorrowmoss) and fire (firebloom) to directly attack an enemy, or use stormvine seed to cause vertigo on a tile right next to chasms where they can fall thought. Using stormvine to kill a tough enemy in one hit is always satisfying.