Citrus hystrix – Kaffir Lime

Site: Choose a warm, sunny, sheltered position out of frost and cold wind, within easy reach of the kitchen.

Soil preparation: Work generous compost and aged manure through the bed to build the humus content this species prefers.

Hole: Dig twice as wide as the root ball and the same depth.

Planting: Set level with the surrounding soil, backfill gently, firm in and water deeply. Mulch straight away to hold moisture.

Home orchard: 2.5 to 3 metres apart so each canopy fills out and leaves are easy to reach.

Informal screen: 2 metres apart for a low thorny screen that also supplies leaves.

Pot or container: A pot of 50 to 60 centimetres suits a single tree in a courtyard or beside a kitchen door.

Watering: Water deeply twice weekly through the first 12 months, then keep moisture even through the warm months. Dry stress causes leaf drop, which is the crop.

Mulching: Apply a 5 to 7 centimetre layer of organic mulch over the root zone, keeping it 5 centimetres clear of the trunk.

Pruning: Harvesting leaves does most of the pruning. Pick from across the whole tree, and thin crowded interior wood in late winter. Wear gloves for the thorns.

Fertilising: Apply a complete citrus fertiliser in early spring and again in midsummer to keep new leaf flushes coming.

Pest and disease: Citrus leaf miner is the main problem because it distorts the leaves you want to pick. Inspect each flush, and watch for scale and aphids in humid weather.

Citrus hystrix performs best in humus rich, free draining loam at a slightly acidic to neutral pH. It dislikes both waterlogging and drying out, so structure and mulch matter.

Sandy soil: Workable if compost is added and mulch is maintained to hold moisture.

Clay soil: Plant on a raised mound and improve with gypsum and coarse organic compost.

Loam: The preferred soil, giving even moisture and steady leaf production.

pH: Slightly acidic to neutral preferred. Mulch with composted leaf litter to maintain levels.

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.