Pot or root bound plants need to be re-potted into a larger pot. Do not go up more than two sizes in your pot. Place a piece of coffee filter paper over the bottom of the new pot, (works better then...
Burdock grows to 5 ft (1.5 m) tall producing purple hued leaf stalks longer than the leaves, resembling rubarb in size and shape, flower heads are round and surrounded by stiff, prickly, hooked burrs.