Insect flowers, from which pyrethrum or insect powder is prepared, are produced by several species of plants of the aster family which occur wild in the eastern Mediterranean region, where they are also cultivated.

The species here considered (Chrysanthemum [Pyrethrum] cinerariaefolium) has been cultivated commercially in California for the production of insect powder. This species seems to thrive best in warm situations and should grow well in any good soil which is well drained and not too heavy. The seeds may be sown directly in the field, either early in the spring or in the fall, but it is preferable to start the plants in coldframes or well-prepared seed beds and transplant them to the field. The seed is mixed with sand and sown broadcast on the surface of the bed and lightly covered with a rake. Water should be used sparingly on the seed bed, since the young seedlings and even mature plants are easily killed by a wet soil. When the seedlings are about a month old they are transplanted, during damp weather if possible, and set 8 to 12 inches apart in rows 3 to 4 feet apart. Old plants may also be divided and used for propagation. The plants should be well cultivated during the growing season and will yield flowers for several years if they are well cared for. The fertility of the soil is maintained by the application of fertilizers.

The time of harvesting varies from June to September, according to locality. The flower heads are gathered just as they open and may be collected by hand or by means of a flower picker. They are dried, preferably in the shade, on canvas sheets about 15 feet square, on which they are spread in a thin layer and turned two or three times a day until dry.

The average yield of dried flowers appears to be about 450 pounds per acre. The wholesale price for these flowers in June, 1920, was 85 to 90 cents a pound, which is from three to four times the prewar price.