Isodon japonicus

Isodon japonicus is a perennial, a plant that lives for years. It belongs to the mint family, Lamiaceae. Its native range runs from northern and central China to Korea. It also grows wild in central and southern Japan. Kew places it in the temperate biome, a broad climate zone. The RHS gives Plectranthus japonicus as another name for it. It is not native to Britain or Ireland.

Plants For A Future gives its height as 3.3 feet [1 metre]. It lists wild sites on hills, in thickets, and in valleys. These range from sea level to 6,890 feet [2,100 metres]. The sources give no mature spread or growth rate. They give no details on stems or leaf shape. Each flower has both male and female organs. The sources do not state flower colour or bloom season. They give no details about the fruit.

For gardens, Plants For A Future lists sun or light shade. A sunny woodland edge fits the settings it lists. So does a site with dappled shade. The plant prefers moist soil. The same source lists sand, loam, and clay as suitable soils. It accepts slightly acid, neutral, and slightly alkaline soil. These records suggest a range of garden sites. Yet little is known about how to grow it. No source states how much water it needs. None shows how well it copes with drought or dry spells.

How well it survives British cold is not clear. Plants For A Future suggests it may live outdoors there. It bases this view on the plant's native range. This is not a tested rating for cold hardiness. Its seed advice is tentative, not tested for this species. It suggests sowing in spring in a cold frame. Give the seeds just a thin cover. Move seedlings to their own pots when large enough to handle. This method keeps them under cover for their first winter. Plant them out in spring. Spring division may work, but the source does not confirm this.

Plants For A Future records cooked young leaves as food. It rates the plant low for food use. It also notes use as medicine for stomach cancer. That record does not prove it is safe or works. The source lists no known hazards. This does not mean the plant is safe. It reports no other uses and flags no weed risk. The sources name no pests or diseases. They give no basis to judge how well it resists either.