[Overview]
An annual, biennial or perennial that is bluish purple overall and has a metallic sheen.
Leaves are simple and alternate, often with cuts, and have spiny teeth on the margins.
Many small flowers are borne in spherical to cylindrical flower heads, surrounded by spiny bracts.
The flowers are white to blue with 5 petals.
The tips of the calyx are usually spiny.
[Cultivation]
Propagate from seed or by division.
Because it grows wild in cool, dry climates, it prefers well-drained sandy soil.
Grow it in a sunny, well-ventilated place.
To keep the base of the plant from becoming too wet, plant it shallowly on a mound of soil.
It has a taproot and dislikes being transplanted.
It dislikes heat and humidity, so in midsummer move it to a well-ventilated partial shade or provide shading.
For potted plants, water thoroughly when the soil surface dries.
For plants in the ground, rainfall is sufficient.
It is weak against excess moisture, so it is better kept somewhat dry.
During long rainy spells, place it where rain does not reach, such as under the eaves.
Apply chemical fertilizer in spring and autumn.
There are no particular pests or diseases.
