Travel to the caves at (6358,3124) and (6442,3206). Use the on the Hallowed Sourcestone Bell onStrange Pulsing Seeds that are found there. Slay each of these Glastig Roots.
After both are dead search the Aelfwar nearby for a 1st Order Druid with only 75% health (found patrolling at 6543,3097). Use the bell one more time on this druid to summon Glastig the Green Lady. Both the roots and Glastig are 20 elite and hit very hard, bring friends.