Q: What is a kaffir lime tree?
A: Citrus hystrix is a thorny evergreen citrus native to Southeast Asia, also sold as makrut lime. Its distinctive feature is the double lobed leaf, which looks like two leaves joined end to end and carries a citrus aroma unlike anything else. Leaves, not fruit, are the reason it is planted.
Q: What are kaffir lime leaves used for?
A: They are a staple of Thai, Lao, Cambodian and Indonesian cooking, shredded finely into salads or dropped in whole to flavour curries, soups such as tom yum, and stir fries. The aroma is released by tearing or bruising the leaf. Leaves freeze well, so a single tree covers a year of cooking.
Q: Is kaffir lime the same as makrut lime?
A: Yes. Makrut lime is the Thai derived name for Citrus hystrix and is increasingly used in preference to the older term. Both names refer to the same plant, so nurseries and recipes using either one are describing identical trees and identical leaves.
Q: How big does Citrus hystrix grow?
A: It reaches 2 to 4 metres tall and 2 to 3 metres wide, and regular leaf picking naturally keeps it smaller and bushier. Growth is moderate and slows markedly in cool weather. Because harvesting is itself a form of pruning, most trees settle at a comfortable height without any deliberate shaping.
Q: Is kaffir lime frost tolerant?
A: No, it is frost sensitive and cold damages the very foliage you are growing it for. It is reliable outdoors from the Sydney basin northwards and in warm sheltered gardens further south. In Melbourne and Adelaide, plant against a warm wall or keep it in a pot that can be moved under cover for winter.
Q: Is the fruit edible?
A: The fruit is edible but has very little juice and a thick bumpy rind, so it is used mostly as zest in curry pastes rather than squeezed. Do not judge the plant by its fruit. Leaves are the crop, and the knobbly limes are best treated as a curiosity and a source of rind.
Q: How do I care for a kaffir lime tree?
A: Water consistently and never let it dry out badly, mulch the root zone, and feed with citrus fertiliser in early spring and again in midsummer. Pick leaves from all over the tree rather than stripping one branch. Wear gloves for the thorns and watch for citrus leaf miner, which distorts new growth.