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.