Pyrethrum daisy's scientific name is Chrysanthemum cinerariaefolium. It is also known as Pyrethrum roseum, Chrysanthemum roseum and Chrysanthemum coccineum. This perennial is native to southwestern Asia and is considered noninvasive to North America. Pyrethrum develops delicate fernlike foliage with 1-inch daisylike blossoms in May and June. Red, pink, purple or white petals surround yellow middles on top of erect stems. These flowers can be single or double blooms. Pyrethrum grows 12 to 24 inches high and spreads up to 24 inches wide.
Pyrethrum seeds germinate in 1 to 2 weeks when the weather is 60 to 70 degrees F. in the spring. Fertilize pyrethrum during its blooming season during the summer. It is usual to stake pyrethrum for support shortly after it starts to grow. The dwarf types do not need staking. Mow pyrethrum down in June after the first bloom begins to fade to promote a second bloom in fall. This second bloom will not be as prolific as the first bloom. Division or stem cuttings are propagation options. Pyrethrum prefers to be rooted in sand and must be well watered as it develops its root system.
Pyrethrum is hardy in zones 3 to 7. It thrives in areas where the minimum temperatures in the winter are between -40 to 10 degrees F. Its growing range extends from Minneapolis, Minnesota to Little Rock, Arkansas. Pyrethrum grows best in the cooler climates, but it needs winter protection when exposed to severe temperatures.
Too much rain and standing water in the spring can be fatal to pyrethrums. This depletes the oxygen level near the roots right when the plant begins to wake up. Pyrethrums can become infested with aphids, Chrysanthemum nematodes and leaf miners. Encourage beneficial insects in your garden to help keep harmful insect populations under control.
Pyrethrums were recorded in history 2,000 years ago in the Silk Route trading documents from China's Chou Dynasty. It was mentioned growing in the Dalmatian region which is present-day Croatia. In 1804 to 1815, during the Napoleonic Wars, crushed pyrethrum flowers were used by French soldiers to control fleas and body lice. Pyrethrum was marketed as Dalmatian Flea Powder during World War I.
Pyrethrum is commonly used for cut flowers in bouquets. Natural insecticide pyrethrins are made from the powdered, dried flower heads. This is a fast-acting contact poison that paralyzes insects. Pyrethrins are used to control mosquitoes, houseflies, aphids, scale, spider mites, thrips and fleas. These ingredients are also used in flea spray and insecticidal soap. Pyrethrins have a long safety record, low toxicity to mammals and breaks down quickly in sunlight. This natural insecticide is lethal to fish, bees and beneficial insects.
Pyrethrums come in many different varieties. James Kelway is a dark red blossom type. Roseum, Brenda and Eileen May Robinson are pink flowered. Mont Blanc's blooms are pure white. Mrs. James Kelway starts out as a creamy white blossom that turns to a pale pink.