Water the soil around the sweet William thoroughly the day before you want to remove the plant. This softens the soil and makes removal easier.
Grasp the plant by the base, as close the soil as possible. Pull up firmly to remove the plant from the soil. Pull out as much of the root ball as possible.
Use a hand spade to dig around the roots if the plant will not come up easily. Insert the spade into the soil 4 inches from the base of the sweet William at a slight angle. Push down on the handle to uproot the plant, then pull it until it is clear of the soil.
Knock the loose soil off the roots. Dispose of the sweet William in the trash or compost pile.