After clearing mobs in the garden, seeds will drop.
Plant these seeds in the pots and find a Dark Nependeath and a pot that cannot be planted.
After killing the Dark Nependeath, the boss will appear.
After killing the boss, an Even Stranger Seed will drop, then plant this seed in the pot that cannot grow Nependeath.
After planting the seed, a Life of Grass will grow. Take the Life of Grass and return to Central Tower and place it in the middle of the Statue to complete the party quest.