When it meets a plant, the Heal Weed will begin to drop sun-drops to heal that plant every 3-5 seconds or so. It is the plant counterpart of the Heal Zombie.
In Backyard Battleground, Heal Weeds, if a player gets close enough to one, have a tendency to start following after the player exclusively, completely ignoring other plants, even if the player is at full health.
It will not stop following the player unless the player gets far away enough or the player activates the Cactus' Garlic/Artichoke Drone. The same goes for the Flag Weed.