[Overview]
A perennial, but because its cold tolerance is weak it is treated as an annual in Japan.
It is grown for its brightly colored leaves.
Leaves are simple and opposite, with toothed margins.
The flowers are borne in large numbers in spikes; they are small, two-lipped, and blue to pale blue.
The fruit is a schizocarp.
[Cultivation]
Propagate from seed or by stem cuttings.
The optimum germination temperature is high, 20–25 °C, so sow around May, do not cover the seed with soil, and water from the bottom.
Stem cuttings are possible at 15 °C or above.
If brought into a sunny room in winter, it can overwinter and be grown as a perennial.
It prefers fertile soil with good sun, drainage, water retention and aeration.
It prefers a well-ventilated place that does not dry out.
Direct sun in summer fades the leaf color, so move it to partial shade in midsummer.
For potted plants, water thoroughly when the soil surface dries; for plants in the ground, rainfall is sufficient.
However, if the soil dries out in midsummer, water in the morning or evening when temperatures are low.
Apply slow-release fertilizer as a base fertilizer; giving liquid fertilizer once a week until autumn improves the leaf color.
Flowering fades the leaf color, so cut off the flower buds when they appear.
Pests and diseases include armyworms and slugs.
