Plant 6 Growth-blessed saplings in the following locations (marked with blue dots on the in-game map)
( 4039, -849, 359 ) Copy/waypoint 4039, -849, 359
( 3866, -862, 346 ) Copy/waypoint 3866, -862, 346
( 3729, -862, 405 ) Copy/waypoint 3729, -862, 405
( 3506, -867, 374 ) Copy/waypoint 3506, -867, 374
( 4028, -836, 100 ) Copy/waypoint 4028, -836, 100
( 4123, -842, -89 ) Copy/waypoint 4123, -842, -89 - this one may be guarded by Mangla the Repeller
Note: Plant locations "respawn" after about 30 minutes real time. If Mangla won't let you near the last planting spot, just wait for one of the others to respawn.
Defeat 6 forest retaliators, then tell the forest spirits to inhabit the saplings.