Green Ear( Complete Adventurer, p. 110)
Your bardic music can affect plant creatures.
Perform (any) 10 ranks, bardic music,
You can alter any of your mind-affecting bardic music abilities (or similar Perform-based abilities from other classes) so that they influence only plant creatures instead of other creatures. However, plants receive a +5 bonus on Will saves against any of these effects.
Plants are normally immune to all mindaffecting spells and abilities.