Kumquat is a smallish tropical fruit-bearing tree that has the advantage of being extremely attractive as a landscape plant, both in the garden and in a large patio container. This broadleaf evergreen tree has deep-green glossy leaves and produces olive-sized fruit that resembles a miniature orange in size and color. Once classified in the Fortunella genus, the kumquat is now classified as Citrus japonica, joining the same genus as oranges, lemons, and similar fruit-bearing trees.
Kumquats are some of the easiest fruit trees to grow in garden pots. The most commonly grown type is the 'Nagami', which has oblong fruit. When ripe, kumquat fruit has a sweet, edible skin with slightly sour meat inside.
|Botanical Name||Citrus japonica|
|Plant Type||Flowering broadleaf fruit tree|
|Mature Size||8 to 15 feet tall (smaller when grown in pots)|
|Sun Exposure||Full sun|
|Soil Type||Moist, well-drained loamy soil|
|Soil pH||Neutral to mildly acidic|
|Bloom Time||Late spring|
|Hardiness Zones||9 to 10|
|Native Areas||China, India, Japan, Taiwan, the Philippines|
How to Grow
Plant a kumquat tree in a sunny site with fairly loose, well-draining soil. It will not do well in dense clay soils. Keep the soil moist but not soggy for the first few years. Once established, they require deep watering only during dry spells. A layer of mulch over the root zone will help preserve soil moisture, but keep the mulch several inches back from the trunk to avoid fungal problems. Kumquats are self-pollinating, so a single tree will produce fruit.
Kumquats are often grown in large patio containers. In any area with freezing temperatures, the exposed roots should be covered when temperatures dip. In regions with long winter cold, the potted trees can be brought indoors to a bright sunny location, then returned outdoors in the spring.
Kumquat trees need full sun; they do best with at least six hours of sunlight a day. When your plant is inside, give it as much light as possible. You can place it in a sunny window (though be careful that too much direct sun doesn't burn your plant), or set it under grow lights or shop lights fitted with one cool and one warm bulb. Your kumquat will also survive if you give it bright, indirect sun.
Kumquats do well in soil with any pH, but if you choose to grow them directly in the ground, add a high-quality potting soil to enrich the soil and improve drainage. Do not plant kumquats in dense clay soil, as root rot is likely. You can add a layer of pebbles or gravel to the pot (or to the hole in the ground) to ensure proper drainage.
A potting soil designed for cactus or citrus is ideal for growing kumquats in pots, but any general-purpose potting soil will work.
Proper watering is one of the keys to growing any citrus plant, but particularly those grown in pots. The aim is to keep the soil moist but not wet. Stick your finger into the soil, at least up to the second knuckle. If you feel dampness at your fingertip, wait to water. If it feels dry, water your plant until you see it run out of the bottom of the pot. If your plant is indoors, particularly in winter when the heat is on, misting the leaves with water can help keep your kumquat tree happy. It's also a good idea to use pot feet, so your plant doesn’t sit in water.
Outdoors, a thick layer of mulch over the root zone will keep the soil moist. The first few years of growth are especially important for keeping the plant's roots moist.
Temperature and Humidity
Kumquats are hardy to down to 18 degrees Fahrenheit and should be brought inside or protected (covered with a blanket) if temperatures dip lower than that. This is a plant suitable for garden planting or permanent outdoor pots in zones 9 and 10, but in colder regions is should be a potted plant that is brought indoors for winter. In spring, bring your tree outside and put it in a sunny, protected spot when nighttime temperatures are consistently above freezing. When moving the tree back outdoor in the spring, harden it off with progressively longer visits outdoors over several weeks before moving it to its permanent summer location.
Ideal humidity levels for kumquat is 50 to 60 percent. A humidifier or regular misting may be necessary if your indoor winter conditions are drier than that.
Withhold feeding for the first two or three months, then feed regularly during the growing season. Stop fertilizing in the heart of winter. In the spring, feed your kumquat with a slow-release, all-purpose, or citrus fertilizer. During the growing season, regular applications of a diluted liquid fertilizer, such as liquid kelp, fish emulsion, or a seaweed and fish emulsion combination is a good idea. Water well before and after applying fertilizer to prevent burning the plant.
Kumquats are grafted trees, so make sure to cut away any suckers sprouting below the graft bud, as these will not produce fruit. When the tree is very small, pinching off the tips of the shoots will encourage it to branch out. If you want to prune to shape the tree, do this after the fruit has been harvested, but before the following spring's flowers appear.
Potting and Repotting
Repot your kumquat every two to three years into a container that is slightly larger than the original. These plants do not like to be rootbound. The best time to repot citrus is the beginning of spring, during the leaf-growing stage.
Propagating Kumquat Trees
Kumquat trees are produced by grafting fruit-bearing branches onto the rootstock of oranges and grapefruits. If kumquat seeds are planted, they will not produce viable trees.
Varieties of Kumquats
- Citrus japonica 'Nagami', the most popular type of kumquat, is oval in shape and has deep-orange fruit with two to five seeds per kumquat.
- Citrus japonica 'Meiwa' is larger than 'Nagami', has a sweeter pulp and juice, and is nearly seedless.
- Citrus japonica 'Marumi' is round and bears orange-like fruits. All varieties grow nicely in a container.
- Citrus japonica 'Centennial Variegated' is a compact form growing 7 to 10 feet tall with leaves and fruit that are both variegated.
Harvesting the Fruit
Kumquats are ripe when their skin is a deep orange color and the fruit is slightly soft to the touch. Use a knife or scissors to cut off the fruit so you don’t risk damaging the plant by pulling off a larger piece than intended. Cutting off the fruit with a small piece of branch with leaves attached makes a lovely decoration.
Growing in Containers
Kumquats grow beautifully in containers, whether you choose plastic, wood, or a stone garden pot. Use the largest container possible (at least five gallons) and be sure that it has good drainage. If you're concerned about soil escaping out of large drainage holes, you can cover the holes with a screen. Keep the container raised for good air circulation, being careful not to block the drainage holes.
Common Pests and Diseases
Potted kumquats are susceptible to mealybug infestations and root rot diseases. Combat this by avoiding excess moisture and making sure the soil is well-drained before planting. Also, avoid piling mulch around the base of the tree. Aphids can also be troublesome, although natural predators usually keep them at bay. Horticultural oils used early in the season can help, and if needed, you can treat the tree with insecticidal soap (follow the instructions on the label exactly.) Store any unused insecticide in its original container and out of the reach of children.