- A weak melee attack.
As melee-only units with an attack that rarely causes more than a few points of damage, Seeds are little threat except in great numbers. Barring misses and glancing blows, heroes can usually kill Seeds in a single attack. For this reason, it is often best to ignore Seeds while more dangerous Cadence such as Bulwarks, Twinklers, or Wrinklers are engaging the heroes, though if a hero can't meaningfully attack one of those targets, it certainly doesn't hurt to kill a Seed.
But as more Seeds engage the heroes, it does eventually become more important to reduce their numbers. This usually only happens when fighting Cradles, as a Cradle can potentially add one Seed to the battle every turn and spawns three Seeds upon death. A rough rule of thumb in the early game is to focus on Seeds once there are at least five of them threatening your heroes, especially if they are all clustered around a single hero or if there are other Cradles around likely to produce even more Seeds. As the health and armor of heroes improves, though, it may be safe enough to wait until there are six, seven, or even more Seeds in the fight before culling their numbers.