Pyrethrum plant, Tanacetum cinerariifolium, flower heads are dried and powdered for use as an insecticide. The basis of some commercial insecticides. Pyrethrum paralyses insects but has little to no effect on mammals. A companion plant. Pyrethrum plant is native to Europe. Prefers a moist free draining soil with free lime, in an open sunny position. Drought and frost tolerant. A perennial plant, growing to 0.6m x 0.6m.