It is a kelp garden behind Squidward's house. It has green kelp surrounded by black rocks around the base of the plant.
Role in series
A kelp garden is first mentioned in the episode "Mermaid Man and Barnacle Boy" when SpongeBob asks Barnacle Boy if he remembers the time that the Atlantis food supply was so low that he had to invent a ray gun that makes things grow six times their size to shoot at the kelp gardens.
In "Giant Squidward," SpongeBob and Patrick cut Squidward's kelp garden down because it was used to build the Kelp Mâché Clarinet. Kelp Grow is used to grow it into a larger size.