Evil turnip seeds are used to grow Evil turnip vegetables used in Summoning to summon Evil turnip familiars. A player may plant the seed at level 42 Farming, behind Draynor Manor (on the west side) in an Evil Turnip patch. It takes 4 minutes 30 seconds to grow. Once it is grown, a knife may be used on it to make it a Carved evil turnip. The farming patch does not need any attending (such as watering, curing disease, or using compost). Only a rake and a seed dibber are required. There is a Tool Leprechaun accessible from the Belladonna patch just south of the Evil Turnip patch.
The examine text refers to the popular expression that something is the "root of all evil." The expression of something being the "root of all evil" is itself a reference to Bible verse 1 Timothy 6:10 which is commonly misquoted to say that "money is the root of all evil".