Kumquat Plant Profile

Nagami Kumquat or Cumquat

Kerry Michaels

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 large patio containers. 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. Kumquat trees are considered to be heavy fruiters, with some varieties flowering and producing fruit twice per year. New starts or grafts may need two or more years of growth and strengthening before they're ready for reliable fruiting. Buying larger trees may give you fruit in the first year. In favorable conditions, an outdoor tree can grow up to 24 inches per year. The best time to plant or transplant a kumquat tree is late winter or early spring, after all threat of frost has passed.

Botanical Name Citrus japonica
Common Name Kumquat
Plant Type Flowering broadleaf fruit tree
Mature Size 8 to 15 feet tall, 12 feet wide; smaller when grown in pots
Sun Exposure Full sun
Soil Type Moist, well-drained loamy soil
Soil pH Slightly acidic to neutral (6.0 to 7.0)
Bloom Time Late spring to early summer
Flower Color White
Hardiness Zones 9 to 10 (USDA)
Native Areas Asia
Toxicity Non-toxic

How to Plant Kumquat Trees

Kumquats are self-pollinating, so individual plants can fruit on their own. In ideal conditions, outdoor plants can reach 15 feet in high and 12 feet in width, but container-grown plants typically stay much smaller, at about 5 to 8 feet tall. Outdoor plants need protection from freezing temperatures in zones 9 to 11. In colder areas, kumquats must be grown in containers that are brought indoors before the first frost.

Kumquat Tree Care

Light

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.

Soil

Kumquats do well in soil with any pH, but slightly acidic soil is ideal. 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.

Water

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. 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. 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. Once established, kumquat trees typically require deep watering only during dry spells.

Temperature and Humidity

This is not a frost-tolerant plant. In zones 8 and below, bring potted plants indoors for the winter. After the last frost in spring, you can bring your tree outside and put it in a sunny, protected spot when nighttime temperatures are consistently above freezing. However, be sure to 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. 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.

Fertilizer

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, give your tree regular applications of a diluted liquid fertilizer, such as liquid kelp, fish emulsion, or a seaweed and fish emulsion combination. Water well before and after applying fertilizer to prevent burning the plant.

Varieties of Kumquats

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.

  • 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 Kuquats

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.

Pruning

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 the tree for shaping, do this after the fruit has been harvested but before the following spring's flowers appear.

Potting and Repotting Kumquat Trees

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.

How to Grow Kumquat Trees in Pots

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 applied 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.