Mentha canadensis (American wild mint, "Hakka")

Japanese name: ハッカ （薄荷）
Scientific name: Mentha canadensis

[Overview]
A perennial 20–50 cm tall, growing in wetlands and beside ditches.
The stems and leaves are hairy, and the whole plant has a strong fragrance.
The stem is square in cross section.
Leaves are simple and opposite, oblong to narrowly elliptic, 2–8 cm long and 1–2.5 cm wide, with hairs on both surfaces.
The leaf margins are toothed.
The petiole is 0.5–1.5 cm.
Whorled cymes arise at the stem tips.
The flowers are two-lipped, 4-lobed, and pale purple.

[Uses]
It is cultivated as a herb and used for herbal tea, potpourri, flavoring in cooking and the like.
Besides being used medicinally, its essential oil is famous as peppermint oil (hakka-yu).

[Cultivation]
Propagate by division or by cuttings.
It prefers sun to bright shade and slightly moist, well-drained soil.
It is hardy and spreads by underground stems, so when planted in a garden, it is better to make a barrier underground to keep it from spreading too much.
For potted plants, water when the soil surface dries.
Fertilizer is not particularly necessary, and too much weakens the fragrance.
It is strongly drought tolerant and also tolerates heat and humidity, but when the branches become crowded, they become stuffy and disease may occur.

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