Zanthoxylum piperitum aka Japanese Pepper

Zanthoxylum piperitum belongs to the citrus family, Rutaceae. Its common names include Japanese prickly ash and sansho. It grows wild in China, Japan, and Korea. In Japan, it grows in hill and mountain scrub and hedges. This deciduous plant forms a dense shrub or small tree. Its bushy shape suits beds, borders, and woodland garden edges.

RHS gives a garden size of 5–8 feet [1.5–2.5 metres] tall and wide. Oregon State reports larger plants, reaching 15 feet [4.5 metres] in both dimensions. RHS lists five to ten years to reach full size. The stems bear pairs of flat spines at each node. Alternate, pinnate leaves carry 11–23 small, oval leaflets. These glossy, dark green leaflets turn yellow in autumn. The leaves, bark, and fruit all have a scent.

Small yellow-green flowers grow in clusters in early summer. Tiny red fruits follow the flowers. The ripe fruit splits open and exposes black seeds. These fruits add interest after the flowers fade. The scented foliage and autumn colour also give the shrub garden value. Its spines need care when handling the plant. RHS advises gloves and other protective gear for this work.

Grow it in fertile soil that drains well. Full sun suits it, though light, dappled shade also works. RHS lists chalk, loam, and sand as suitable soils. It accepts acid, neutral, and alkaline soil conditions. The supplied RHS data gives a dry-to-moist soil range. RHS rates its cold hardiness as H6. PFAF lists USDA zones 5–9; Oregon State confirms zone 5 hardiness. RHS places it among plants for low-maintenance borders and beds. It reports few pest or disease problems. Growers can raise plants from seed or use cuttings. Semi-ripe cuttings need bottom heat in midsummer. Root cuttings are another option in late winter.

Food use and safety reports differ between the sources. PFAF records fruit, seeds, leaves, and bark as seasonings. It describes young leaves eaten raw or cooked. Oregon State also records ground seeds as a Japanese seasoning. Yet RHS warns against eating the fruit, including for pets. PFAF reports medicinal uses but notes toxicity at larger doses. Those doses can harm the central nervous system. These records do not establish that all uses are safe. In Japan, craftspeople also make pestles from the wood.