Rakweed Rakweed was an infectious plant from the planet Raxacoricofallapatorius . Biology . Rakweed was a small green plant with a red flower at the top . As the name suggested , it was an extremely adaptable and fast - growing weed . It could grow nearly anywhere and at incredible speeds . Its DNA would adapt quickly to deal with threats and individual plants could also communicate with each other by a high - pitched screeching sound . This connection could be broken by another high - frequency sound at 1421 . 09 Hertz , which would result in the destruction of all plants and spores within the sound ' s range . The Rakweed could produce large amounts of spores . The spores served two purposes ; to increase the Rakweed ' s number , and to infect life forms which were considered dangerous to the plant . Those who were affected by the spores would suffer a distinctive red and black rash , become weaker and enter into a deep coma which they might never waken . Despite this , Rakweed was still edible to both Raxacoricofallapatorian s and human s , and was known to be addictive to Raxacoricofallapatorians . ( TV : " The Gift " ) History . Tree Slitheen - Blathereen had genetically engineered a strain of Rakweed that grew faster than normal . He and Leef gave a potted Rakweed to Sarah Jane Smith as a " gift " for stopping the Slitheen , which she reluctantly accepted . Unknown to Sarah Jane , the Rakweed flowered the next morning , and as a result it spread , just as the Slitheen - Blathereen had planned . The spores ' first victim was Sarah Jane Smith ' s son , Luke Smith . The Rakweed spread quickly around the local area , threatening to engulf the whole of London in a matter of hours . However , Rani and Clyde discovered the plant ' s weakness , prompting Sarah Jane to have Mr Smith transmit the sound of the bell across all audio systems in the affected area . The Slitheen - Blathereen were addicted to Rakweed and would gorge themselves upon the food . Sarah Jane later used this to her advantage , having Mr Smith replicate the bell ' s noise , destroying the Rakweed in the Slitheen - Blathereens ' stomachs . This resulted in the creation of a deadly amount of methane gas , causing the Slitheen - Blathereen to explode or , as Clyde put it , " fart themselves to death " . ( TV : " The Gift " ) Sometime after this events Sarah Jane Smith was kidnapped by the Slitheen - Blathereen . They told Rani Chandra that they would condemn Sarah Jane Smith to a life in exile unless Rani helped to grow the Rakweed until it would cover the Earth . To save Sarah Jane Smith Rani did as she was told . Sarah Jane was released but the Rakweed still grew and it would cover the Earth soon . Furthermore , Luke Smith got infected by its spores again . The Slitheen - Blathereen thought that they had won . ( WC : " Plants " ) Mr Smith and Clyde Langer had a plan to stop the Rakweed . They used Haresh Chandra ' s electric guitar to make the same sounds and vibrations as the school bell of the Park Vale Comprehensive School , which had destroyed the Rakweed before . The guitar sound broke the plants ' communication methods and neutralised the Rakweed spores . This killed off the Rakweed and saved Luke ' s life . ( WC : " Sound " ) References . The spread of " alien plant life " throughout London was one of several alien incursions which occurred in the " Ealing Triangle " , cited by Ruby White when she met Sarah Jane and her team . ( TV : " Goodbye , Sarah Jane Smith " ) While voicing his suspicions about the SerfBoard , which Mr Smith scanned to be safe , Clyde mentioned Rakweed as one of the things Mr Smith scanned as safe but was actually deadly . ( TV : " The Man Who Never Was " )