Do you love Thai cuisine? If you do, then you’re probably aware of the elements that go into a good Thai curry. And you can grow an essential ingredient in your own garden. If you’re into stir fries, and tangy lime zest, try growing a kaffir lime tree!
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Although these trees are native to tropical southeast Asia, it’s very easy to cultivate them outside that region. With a little shifting in the colder seasons, you’ll have kaffir lime all year round. Alternately, skip that outdoor growing altogether and grow kaffir lime indoors.
Citrus plants may be large in their native habitats, but they maintain a small size easily in the right conditions. Your trees could be residents of a greenhouse, patio, or they can be grown indoors. Watch out for the thorns, though!
Let’s discuss what could be your new favorite potted plant, or even your favorite tropical to cultivate in the southern United States.
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Quick Care Guide
All About Kaffir Limes
Kaffir lime or makrut lime (Citrus hystrix) originated in Southeast Asia. The word “kaffir” has been attributed to a racial slur referring to non-Muslim Swahilian Africans who were stolen from their lands during the Indian Ocean slave trade. The Kaffirs were also an ethnic group in Sri Lanka who descended from Bantu peoples.
With recent changes in political views of common names, many restaurants and grocery stores use the name makrut lime. It turns out that micrantha – a term that refers to a lime with a long lineage – is the same species as C. hystrix. In the interest of compassion, many choose to use the term makrut instead when referring to this citrus plant.
This citrus tree is an evergreen bush that stands anywhere from 6 to 35 feet tall. The double hourglass-shaped leaves with a leaf blade twice the size of the petiole grow on thorny branches from a central trunk. In spring, four to five-petaled white flowers bloom up to 2 inches wide and self-pollinate. They die away and green citrus fruit with a bumpy exterior form where the flower once was. The fruit ripens and forms yellow skin. Home gardeners hand-pollinate kaffir lime when they are grown indoors.
Crushed leaves emit an intense citrus fragrance and carry a delicious flavor into cuisines. The fruit rinds have an astringent flavor put into curry base paste. They’re also zested into spiced rum. The rind is not only used to impart flavor, but is reputed to keep away mosquitos, fleas, and lice. The fruit’s fresh juice is mixed into water and used as a cleaner. The essential oil of makrut is used in multiple industries, including aromatherapy.
Because this plant takes a while to fruit (at least three years from the sapling stage), many gardeners prune it to keep it small enough for a large planter. That’s not an easy feat due to thorns up to 1.5 inches long. Some people even graft less thorny citrus onto makrut to remove some of the thorniness in future growth, although this would produce a mixed fruit tree. Grafting makrut branches onto another citrus rootstock is also common.
Planting
Most people in the Western Hemisphere place their kaffir lime tree in a large planter, at least three feet deep. The kaffir lime tree thrives in the tropics. If you’re living in a tropical region, and you’re growing other tropical plants, plant the kaffir lime tree outdoors in late fall so your tree has time to root into the soil before the summer heat. Do not transplant in the dead of winter in cold weather, or you put the kaffir lime at risk. Place it far from other fruit trees, and away from your house and amenities. Kaffir lime trees reach up to 35 feet tall in optimal conditions.
Dig a hole at least 3 feet wide and twice as wide as the root ball. Amend the soil within the hole to include sand for drainage, and well-rotted compost. Place the kaffir lime tree in the hole, then add average garden soil. Allow the mound of the tree to remain above the soil line, and make sure that any graft joints are not covered. If you live outside the tropics, transplant your kaffir lime tree from the nursery pot into a large container with the same mix of soil that an outdoor tree would have. The Air Pots we have in our store are an excellent choice. When the cold weather hits your kaffir lime trees can then be brought indoors.
Care
Let’s talk about the basic needs and growing conditions for your kaffir lime trees. You’ll have a delectable harvest of kaffir lime leaves all year long.
Sun and Temperature
Makrut trees are tropical and need full sun. That means 6 to 8 hours of sun per day at minimum. The USDA hardiness zone range for these trees is small, ranging from 10 to 12. Kaffir lime leaves produce in high temperatures easily. Triple-digit heat is no problem at all. But when the weather dips below 50 degrees Fahrenheit, protect your tree. Bring it indoors, or cover the aromatic leaves with a commercial frost cloth. If it experiences a hard freeze it may die. Low temperatures (below 50 degrees) will also stunt flowering and fruit production.
Water and Humidity
These plants love high heat and humidity. If you have dry heat in your region, and your tree is outdoors, water a couple of times a week at the base of the trunk. Do so in the morning, and avoid wetting foliage. Overall, about an inch of water per week is adequate with the right humidity. Allow the soil around the tree to dry out in between waterings so as not to waterlog it. Drip irrigation or soaker hoses are optimal for watering, but any other gentle irrigation method works. Do not water if there has been a lot of rain. In the growing season during the fruiting phase, water a few times per week to help fruit form and bulk up.
Soil
The soil around the tree should be average to fertile, and sandy to promote good drainage. Fill a pot or hole in the ground with a good mixture of average garden soil amended with sand and well-rotted compost. Makrut can survive in poor soil, but it especially needs good drainage in the pot or hole where you place it. A pH of 6 to 6.5 is best.
Fertilizing
After the first year of growth, fertilize makrut with slow-release citrus fertilizer 2 to 3 times per year. A few tablespoons are enough, even in mature trees. Apply this at the beginning of spring, the beginning of summer, and the end of summer. Do not fertilize in winter as this may shock the tree. The NPK of the fertilizer should be 2-1-1. Water it in well.
Pruning
Wear strong, thick gloves when pruning this tree because it is thorny and will stab easily. Use loppers. Always prune at the node of each branch unless you’re taking part of the branch due to disease. Prune back branches by a few inches if they display a weeping posture. If you’d like to keep your tree small, it’s important to prune.
Begin by removing any diseased branches. Then, remove any dead branches that are dark brown and dry below the bark. Scratch the surface of the branch to determine if it’s dead. Next, remove small sprouts from the bottom 10 to 12 inches of the tree. Save them, as they can be propagated into new trees. Branches growing toward the base of the trunk should be removed as well. Note that makrut is evergreen, and the leaves will not drop in winter.
Propagation
Those small buds and suckers you pruned off the tree can be rooted in a starter pot. Use a propagation dome, and rooting powder or gel to help the stems get started. Clean cut the end of the cutting, and remove the bottom leaves. Use rapid rooters and place the tip in after they have been dipped in rooting media. Space the cuttings out in your tray so they don’t touch each other. Spray them with water and place the dome over the top of the tray. Place them in an area with low light. Keep the area at about room temperature. It can take anywhere from 6 days to 6 weeks for the cuttings to root.
To graft your lime onto another rootstock (which could be another makrut, or another lime species), take a cutting of a healthy branch and make a 45-degree angle cut along the base of the stem. Then cut a branch of the rootstock, exposing the healthy flesh. Cut just into the bark enough to separate it from the flesh, and place the makrut cutting under the bark. Bind them with plastic, and place a plastic bag around the grafted area, affixing the edge to the rootstock. After a few weeks remove the plastic bag and wrap. If the branches are fused and there is new growth, you’ve been successful.
Harvesting and Storing
Despite the thorns, the stabs, and the pain, harvesting this tree in your garden is so rewarding! Whether you go for aromatic leaves, fruit, or juice you’ll have astringence to pack into dishes all year.
Harvesting
PIck green kaffir lime leaves whenever the tree is mature, in spring when they are fresh. Throw them in with your favorite fish, chicken, or warm spicy foods as needed. If you want to pick a few leaves, doing so by hand is fine. For larger harvests, select an entire branch and carefully remove all the leaves. Gloves are a must here.
Fruit will set about 6 to 9 months after the flowers die away. At this time, test a lime by removing it by hand and cutting it in half. If there is adequate juice, the rest of the limes should be ready. Harvest the fruits when they’re green, not when they’re yellow. The yellow fruits are too bitter to be used in dishes, although the zest is often added to food as a seasoning. In tropical areas, harvest the fruits year-round. In areas outside the hardiness zones, harvest occurs in late summer.
Storing
Wash fresh leaves and store them in a plastic bag with paper towels for one week in the refrigerator crisper. They’ll freeze this way for up to 1 year. To dry them, hang an entire branch upside down in a warm, dark, dry place until they break easily. Store them in an airtight container for 2 years.
Store fresh limes on the countertop with good air circulation for 2 to 4 weeks. They’ll keep in the refrigerator for 1 to 2 months. Cut limes should be consumed immediately or within a day. Lime juice will keep airtight in the refrigerator for 6 months. Freezing is not recommended as it will ruin the texture of the lime, but freezing the juice is fine. The same goes for other citrus fruits, like lemons. Dehydrate the lime to complete dryness, and it will keep up to 5 years in a plastic tub or glass jar. Properly canned and sealed jars of lime last 9 months. Freeze the whole or sectioned lime zest and store it for 1 year. Use this zest in dishes as needed, and smell that lovely fragrance.
Troubleshooting
Now we’ve covered the care, so let’s cover the problems to search for when you check on your tree.
Growing Problems
Grow this tree in an area that is too cold, and it takes on cold damage. At prolonged periods of temperatures below 50 degrees, the tree may become damaged or die. Bring it indoors if you suspect the weather won’t let up.
Growing the tree in a medium that doesn’t have good drainage and remains wet too long creates conditions that stress the tree and put it in danger of contracting a disease. If it dries out too long, the tree will drop leaves and slow flowering, slowing your yield. A lack of nutrients will also slow yield, and show as changes in leaf color. Remember to fertilize 2 to 3 times over the growing season to avoid nutrient deficiencies.
Pests
Ants are a sign that other pests might be around. They tend to harvest the honeydew of other pests like aphids. By domesticating these pests, ants have a food source… and so do the other pests. Mix equal parts of borax, peanut butter, and honey into a paste and fill old bottlecaps with them, setting them around the base of the tree. The ants will harvest the paste, carry it back to their hive, and the borax in the paste will kill the colony. Painting the trunk of the tree with sticky paint such as Tanglefoot Trap will prevent ants from reaching the fruit.
Cottony cushion scale is a common problem among citrus trees. It looks like white fluffy bumps that appear on branches and tree trunks. It’s not a fungus or a disease, though. It’s insects – Icerya purchasi to be exact. They suck sap from branches and can produce honeydew that ants love to drink. If there’s only a few, use a cotton swab dipped in rubbing alcohol to force them to release from the plant and remove them. Neem or horticultural oil will effectively kill these scale insects and other mealybugs off.
Mealybugs, spider mites, leaf miners, and whiteflies are all insect pests that suck sap from the leaves and branches of the makrut tree. Mealybugs look like little cotton wisps that live in colonies in the tree. Spider mites are so tiny that you may not see them until later stages when they spin webs around parts of your tree. Leaf miners travel inside the leaves rather than on the surface, eating the flesh between the cell walls of leaves. They leave small meandering trails on your leaves. Whiteflies are small moth-like insects that feast on the sap of trees at any place.
Search for these insects, and blast them off with a strong stream of water as soon as possible. This usually fixes the issue. Neem oil is effective against the eggs of most of these pests, as it causes the unhatched young to be smothered. It’s also effective against adult spider mites. The citrus leaf miner is a bit trickier to treat; remove leaves that show sign of mining trails and destroy them, then spray the tree regularly with neem oil as the naturally-forming azadirachtin in the oil will gradually penetrate through leaves to take out any remaining larvae. Insecticidal soap is effective against adult mealybugs and whiteflies.
Diseases
Xanthomonas axonopodis pv. citri is the bacteria that causes citrus canker. Yellow ringed lesions appear on all parts of the tree (leaves, branches, and fruit). In later stages, the lesions get a gray fuzzy center and the tree becomes defoliated. Remove damaged parts of the tree as soon as possible. Apply copper fungicide spray per the manufacturer’s directions, being sure to cover all portions of the tree. It’s important to contact your local agricultural extension and let them know you’re dealing with citrus canker as some regions have local regulations that require you to cut down and dispose of the tree due to risks to other trees in the region, and the disease is tracked. Copper fungicide is not guaranteed to fix this canker disease, so you may lose the tree regardless of any attempted treatment.
Greasy spot comes from the fungus called Mycosphaerella citri. It starts as a spot on the underside of leaves that may form a yellow spot on the tops that appears greasy and shiny in the center. It can also impact the fruit, creating dark spots that are referred to as greasy spot rind blotch and which are a significant agricultural problem for fruit sellers. Copper fungicides work to treat this fungus, but are often blended with horticultural oils prior to spraying.
Phytophthora gummosis is the pathogen of two soil-borne organisms that cause foot rot, or the rotting of makrut roots. You’ll notice cracked bark and gumming in the cracks. Just above the roots, you’ll see brown to black bark. Root rot caused by Phytophthora is difficult to treat. You can graft resistant rootstock onto your tree, or use the methods listed for greasy spot to treat foot rot.
Huanglongbing (HLB), also called citrus greening, is a bacterial disease that affects almost all citrus plants. It causes new leaves to take on a blotchy appearance, and for the fruit to contain aborted seeds. The fruit may not ripen on trees affected by HLB. If you find these symptoms on your tree, quarantine it, and contact your local ag extension office. They will have information about the best next steps.
Frequently Asked Questions
Q: How tall does a kaffir lime tree grow?
A: Anywhere from 6 to 35 feet, depending on the conditions.
Q: What is the difference between kaffir lime and lime?
A: Kaffir limes are bumpier, grow on thorny trees, and have a much more astringent smell and taste. The leaves are the most popular harvest from this tree!
Q: Why are kaffir lime leaves so expensive?
A: It’s those dang thorns! Harvest must be done delicately so harvesters don’t get stabbed.
