Explosive Growths are thin plant-like creatures that sprout from the ground around party members standing still in the vicinity of Urgoz. The longer the player stands in one spot the more Growths will sprout.
After a few seconds, they will die, causing an Exploding Spores effect which inflicts exactly 300 elemental damage to adjacent players and knocks them down for several seconds.
It's best to constantly stay on the move while fighting Urgoz.
Because Urgoz inflicts Binding Chains on players, these Growths can quickly overcome those slowed down by that hex.
Explosive Growths are immune to hexes and conditions. The error message states that they are spirits, however this has not been tested with spirit-specific skills such as Consume Soul, Spirit Walk or Spiritual Pain.