Weevil

First, you need to visit the Magic Bean seller in the right side of the Inner Garden. Sneak past the guards patrolling the area, and drop into a hole in the ground. Talk to the guy inside, and learn how to use Magic Beans. You'll need to buy another Magic Bean from him, and collect some Spring Water in a bottle.

Then head back outside the Deku Palace, and jump across the large lilypads to the right side of the palace. Plant the Magic Bean and water it. Ride it to the Outer Garden, using the Deku Flowers to cross the garden. Shoot bubbles at the Mad Scrubs to get rid of them.