Kaffir lime, known botanically as Citrus hystrix, is an evergreen edible citrus fruit tree native to Southeast Asia. It grows well in containers and remains small, reaching a maximum of 10 feet in height at maturity, when cultivated indoors. Like all citrus it thrives in full sun and moderate to warm temperatures. It does not tolerate frost but responds well to high ambient humidity. With ample daily sunlight and moist, nutrient-rich soil, you can successfully grow kaffir lime trees indoors, and you may even be able to produce fruit and flowers.
Choose a growing location with bright direct sunlight for a minimum of 6 to 8 hours each day under or near windows without a UV-blocking coating. Supplement natural light with artificial light from grow lamps, if needed.
Fill a plant container with good-quality, easy-draining potting soil amended with compost. Plant your tree in a container two to three times the diameter of the root ball and with several drainage holes.
Water the tree so that the soil is just moist all the way through and water drains out of the bottom and into a saucer below. Achieve this with deep watering once every six to 10 days, depending on the size of your tree and its growing conditions. Allow the top few inches of soil to become dry before watering again.
Boost the ambient humidity by running a humidifier near your kaffir lime tree. This can be helpful year-round but is particularly important in winter and during arid summers.
Fertilize your kaffir lime with an organic citrus tree food or a complete all-purpose slow release fertilizer designed for flowering plants. Feed over moist soil according to label dosing directions for the size and age of your tree. Water the fertilizer in well.
Transfer the plant outdoors in the spring after the last frost has passed, if desired. Summering the lime tree outdoors will allow pollination to occur. Place the tree in a location with filtered sun or partial shade and protect your tree from winds. Bring the lime tree back indoors before air temperatures cool down to 50 degrees Fahrenheit.