Ageratum (genus, whiteweed)

Japanese name: アゲラタム
Scientific name: Ageratum

[Overview]
An evergreen perennial, but because it is vulnerable to cold, it is treated in Japan as an annual sown in spring.
The whole plant is covered with coarse hairs.
The stems branch freely.
The leaves are simple and opposite, but may be alternate in the upper part of the stem.
The leaves are ovate with serrated margins.
Flower heads about 1 cm across are borne at the stem tips in corymbs to panicles.
The flower heads consist only of tubular florets and are usually pale bluish purple, but white, pink and red also occur.
The fruit is an achene.

[Cultivation]
Propagate from seed, by stem cuttings, or by division.
The seeds need light to germinate, so sow them in seed-starting soil without covering them with soil, and water from the bottom so the soil does not dry out.
The optimum germination temperature 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, go easy on fertilizer.
Too much fertilizer (especially nitrogen-rich) produces only leaves and makes flowering difficult.
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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