Sunflower

Sunflowers are large plants able to stop the Corruption and The Crimson from spreading in Pre-Hardmode. They act as background objects like furniture and are obtained by breaking them with a pickaxe. They are also sold by the Dryad. Sunflowers are not able to stop the Hallow.

Sunflowers can only be placed on grass and hallowed grass above ground. Placing them on corrupt grass or dirt will not work. Sunflowers are 2 blocks wide and 4 blocks tall. They cannot be planted in a plant pot. They also have the ability to spawn more sunflowers in a small area, but the chance is very low. No background walls may be present where the sunflower is placed.

Note that sunflowers no longer stop Corruption (or Crimson) spreads in Hardmode.

They are extremely useful for changing a corruption or crimson biome to a regular one. Use these if you want your world to be corrupt or crimsoned and still have NPCs without setting up a space station for them to live in. See House.