Go to a ripe Broc flower or White Horsenettle plant, and instead of the Use button, press the Grab button. You'll be able to lift the whole plant right off the ground.
If you let it go, it will fall straight through the ground, respawn and fall again. After about 5-6 cycles, it will stabilize itself in its original position again.
It can be done with unharvested and harvested plants of these types, but not with wilted ones.
Works in the PS3 version as well.
EDIT: Went back and doublechecked: you can only grab unpicked plants, but you can pick and grab them while they're "falling".