Ageratum conyzoides (billygoat-weed, "Kakkoazami")

Japanese name: カッコウアザミ （霍香薊）
Scientific name: Ageratum conyzoides

[Overview]
Found along roadsides and in vacant lots, 30–60 cm tall, sometimes 1 m.
In its native range it is an evergreen perennial, but it is sensitive to cold and so is an annual in Japan.
It is covered with many hairs.
The stem branches well and is often tinged with red.
Leaves are simple and opposite, though they are sometimes alternate in the upper part of the stem.
The leaves are ovate to oblong, 5–13 cm long and 2–4 cm wide, with a blunt tip, a rounded to shallowly heart-shaped base, and toothed margins.
The petiole is about 3 cm long.
Leaves become smaller and petioles shorter toward the top of the stem.
Flower heads about 0.5 cm across are borne at the stem tips in corymbs to panicles.
The flower heads consist only of tubular flowers and are usually pale bluish purple or white.
The style is 2-lobed, protrudes far out, and is the same color as the flower.
The involucre is nearly spherical, and the involucral bracts are hairless.
The fruit is an achene, square-prism-shaped and black, with a pappus as long as the corolla tube.

[History]
It was introduced in the early Meiji period and has become naturalized in various places.

[Uses]
It is used medicinally.

[Cultivation]
Propagate from seed or by stem cuttings.
The seed needs light to germinate, so sow it in seed-sowing soil without covering it with soil, and water from the bottom so the soil does not dry out.
The optimum temperature for germination is 15–25 °C.
It prefers sunny, well-drained soil.
Take care not to overwater; for potted plants, water thoroughly when the soil surface dries, and for plants in the ground, rainfall is sufficient.
For plants in the ground, a small amount of base fertilizer is enough and nothing more is needed; even for potted plants, it is better to fertilize sparingly.
If too much fertilizer is given (especially one high in nitrogen), the plant produces only leaves and is slow to flower.
When plants become crowded they get stuffy and prone to disease, so remove crowded branches.
Pests and diseases include gray mold, aphids and spider mites.

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