Bulb (The Mutant Turnip)
Talk about it here.
What the Eleventh Doctor referred to as simply an alien bulb had burrowed underground on a French farm. There it had feasted on the soil's nutrients and grown to a huge size. Its powerful roots drilled through the dirt, attacked those above ground and pulled them under. The bulb was shrunk by a particularly bad batch of Michel's wine belonging to farmers Alain and Simone. The Doctor removed the shrunken bulb to be rehoused somewhere out of the way. (COMIC: The Mutant Turnip)