How to Grow Kumquats

The kumquat is a small, 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 has dark green, glossy leaves and produces olive-size fruits that resemble a miniature orange. 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. When ripe, kumquat fruit has a sweet, edible skin with slightly sour flesh inside. Kumquat trees have a moderate growth rate, gaining up to 24 inches per year. They should be planted in the spring.

How to Plant Kumquats

When to Plant

The best time to plant or transplant a kumquat tree is in the spring after the threat of frost has passed.

Selecting a Planting Site

Choose a spot that gets lots of sun and has good soil drainage. Make sure no nearby taller trees will shade out the kumquat, as this can affect its growth and fruit production. The spot also should be protected from strong winds. If you don’t have an adequate garden site, container growth is a good option. Kumquats also can be grown indoors with enough light.

Spacing, Depth, and Support

Kumquats are typically planted as young nursery trees. Be sure to give a kumquat tree at least 5 to 6 feet of space when planting. The hole for it should be three to five times wider than the root ball and roughly the same depth as the root ball. A support structure typically won’t be necessary.

Kumquat Care

Light

Kumquat trees need full sun; they do best with at least six to eight hours of direct sunlight on most days. When grown indoors, place your tree by your brightest window or set it under grow lights. A kumquat will survive in bright, indirect sun, but it won't be as productive.

Soil

Kumquat trees prefer loamy, moist, well-draining soils with a slightly acidic to neutral soil pH. Don't plant them in heavy clay soils, as this can cause root rot.

Water

These fruit trees like evenly moist but not soggy soil. If you stick your finger in the soil down to the second knuckle and it feels dry at your fingertip, it's likely time to water. A 2- to 3-inch layer of mulch over the tree's root zone can help to maintain soil moisture. Just make sure to keep the mulch at least 3 inches away from the tree trunk, because moisture retention on the trunk can cause diseases and decay and can provide a path for insect and rodent damage.

Temperature and Humidity

Kumquats don't like cold weather, though they can survive temperatures down to 18 degrees Fahrenheit. Ideal humidity levels are 50 to 60 percent. If your tree is indoors during winter when the heat is on and air is dry, use a humidifier or set the container on a tray filled with pebbles and water to raise humidity levels.

Fertilizer

Wait two to three months after planting a kumquat tree before fertilizing. Then, use a citrus fertilizer following label instructions. Don't fertilize in the winter.

Pollination

Kumquats are self-pollinating, which means they don't rely on insects to pollinate them and can fruit on their own.

Types of Kumquats

Some popular kumquat varieties include:

• Citrus japonica 'Nagami' is the most popular type of kumquat. The deep orange fruit is oval in shape and has two to five seeds.
• Citrus japonica 'Meiwa' is larger than 'Nagami', has sweeter pulp and juice, and is nearly seedless.
• Citrus japonica 'Marumi' has small, round, very juicy fruit with a thick yellow-orange rind.
• Citrus japonica 'Centennial Variegated' is a compact kumquat variety that grows 7 to 10 feet tall. It has variegated white and green foliage, and the fruit is streaked with orange and red when ripe.

Kumquats vs. Oranges

At first glance, kumquat fruits might be mistaken for small oranges. However, there are some key differences. Kumquats are slightly more oval than round oranges, and they’re not as sweet. Plus, kumquat peels are edible.

Harvesting Kumquats

Kumquat trees are heavy fruiters, with some varieties flowering and producing fruit twice per year. New starts or grafts might need two or more years of growth before they're ready for reliable fruiting. Buying larger trees might produce fruit in the first year.

The various cultivars can have different harvesting times. Some produce fruits from November to January while others from December to April. 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. The fruit can be used raw or cooked. It will store at room temperature for a few days or in the refrigerator for up to two weeks.

How to Grow Kumquats in Pots

Kumquats grow beautifully in containers, whether you choose a plastic, wood, clay, or stone planter. It's a great option if your climate isn't warm enough to plant a kumquat tree in the garden. Use the largest container possible (at least 5 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 screening. Keep the container raised for good air circulation, being careful not to block the drainage holes.

Pruning

Cut away any suckers sprouting below the graft bud, as they won't 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 flowers appear the following spring.

Propagating Kumquats

Kumquat trees are produced by grafting fruit-bearing branches onto the rootstock of oranges and grapefruits. If seeds are planted, they won't produce viable trees. Most gardeners choose to purchase grafted trees from nurseries rather than trying the technique themselves, as it can be fairly complicated.

Potting and Repotting Kumquats

A potting mix designed for cactus or citrus plants is ideal for potting kumquats, but any general-purpose potting mix will suffice. Plan to 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 is the beginning of spring when leaves are emerging.

Overwintering

In USDA hardiness zone 8 and lower, bring potted kumquat trees indoors for the winter. In the spring, you can bring your tree back outdoors once 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 warm-weather location.

Common Pests and Plant Diseases

Kumquats are susceptible to root rot diseases in poorly drained soil and areas prone to flooding. Aim to prevent this by selecting a planting site with sharp drainage and not overwatering. Moreover, aphids can be troublesome, though natural predators usually keep them at bay. Horticultural oils applied early in the season can help. Also, common indoor houseplant pests, such as spider mites and scale, can afflict kumquats.