Citrus hystrix aka Kaffir Lime

Citrus hystrix, or makrut lime, belongs to the rue family. Other names include Thai lime and leech lime. Kew gives its native range as the eastern Himalaya into China. The range includes Yunnan and northern Guangxi. Kew also lists Wallis Island. It grows in wet tropical climates. Useful Tropical Plants reports no proven habitat in the wild. People grow it for food in Thai gardens and elsewhere.

This thorny evergreen forms a shrub or small tree. Garden plants reach about 8–13 feet [2.5–4 metres] tall. They spread about 3–5 feet [1–1.5 metres] wide. Broader accounts give heights up to 39 feet [12 metres]. Its short trunk can be thin and crooked. The dark green leaves shine and have two distinct parts. White flowers have a scent and add garden interest. Each bloom spans about 0.8 inches [2 centimetres]. RHS reports blooms all year. Missouri lists bloom as seasonal. The fruit has a rough, bumpy rind.

Give plants full sun and shelter from harsh conditions. Under glass, shade them from hot sun. Use moist loam that drains well. Its pH should be acidic or neutral. For pots, RHS advises loam-based compost with no peat. Add grit to the mix. Water well in spring and summer, but less in winter. RHS also advises misting each day while plants grow. Use citrus feed all year. In cool regions, grow it in a greenhouse or conservatory. Plants can stay outside in summer. RHS rates it H3. Missouri lists USDA zones 10–12. It can bear brief frosts from time to time.

Makrut lime suits patios, pots, and courtyards. It also suits warm gardens with shelter. Its leaves stay green and add interest through winter. Growers value its scented flowers and striking fruit, too. Leaves add flavour to soups, curries, salads, and tea. Cooks also use the flowers and fruit rind. The raw fruit is edible but bitter, with little juice. Leaves and peel each yield oils for several industries. People also use the fruit and leaves as hair washes. Past uses on record include insect control and remedies.

Watch for aphids, scale insects, mealybugs, and spider mites. RHS reports few diseases. Soil that stays too wet can cause root rot. To grow new plants, take cuttings in summer. In spring, use layering or sow seeds. Plants take about five to ten years to reach full size. Edible use does not mean the plant cannot harm skin. RHS warns that touching the fruit can cause skin allergies. Sunlight after contact can also harm skin. Wear gloves and clothes that protect you when handling it.