Kumquat Tree (Citrus japonica)

Kumquat tree, also known as Citrus japonica, is an easy-to-grow fruit tree. From all the citrus trees, this one is the most beautiful with dark-green, glossy leaves. It’s known for its bright orange fruits, which are deliciously tart and sweet. These trees, native to eastern Asia, are relatively small and beautiful. If you’re looking to grow them in your backyard, you’ll need to know all the care tips! Keep reading for tons of info.

I. Appearance and Characteristics

Citrus japonica, the round kumquat, Marumi kumquat, or Morgani kumquat, is a species of citrus fruit in the genus Citrus. It was first described by Carl Peter Thunberg in 1780 as Fortunella japonica.

C. japonica is a native species in southern China.

They reach heights of 8 to 15 feet (2 to 4.5 m.) and have a vase-like or rounded canopy. In spring, you’ll be treated to showy, fragrant white flowers. The trees are self-fertile, so you’ll only need one to produce fruit. Growing kumquat trees is easy.

They need full sun and tolerate any soil pH and most soil types as long as the soil is well-drained. They also tolerate seaside conditions. Kumquat trees are suitable to USDA plant hardiness zones 9 and 10, and withstand winter temperatures as low as 18 F. (-8 C.).

II. How to Grow and Care

Sunlight

Kumquat trees thrive in full sun, meaning they need at least six hours of direct sunlight on average. Even better is if you can give it eight to 10 hours of sun, though this can be difficult in the wintertime. Indoors, place your plant’s container by your brightest window, and rotate the plant weekly. If possible, bring your potted kumquat outdoors to a balcony or patio in the summertime to rejuvenate it with plenty of natural light. Not getting enough light can hinder growth and fruit production.

Artificial Light

You may need to mount grow lights over your kumquat tree if you don’t have sufficient sunlight in your home. Your grow light should be quite close to the top of the tre, about 12 inches, and should be left on for a full 12 hours per day. Choose grow lights specifically designed for citrus trees.

Temperature and Humidity

Kumquat trees have a bit of cold tolerance, especially compared to some other fruit trees, and they can even withstand brief frost. But strive to keep it in conditions between 55 and 85 degrees Fahrenheit. Make sure heaters and air conditioners aren’t blowing on them, as this can cause extreme temperature fluctuations, and protect them from drafts near doors and windows. It’s also ideal to decrease the room temperature by 5 to 10 degrees Fahrenheit at night to mimic outdoor conditions.

Kumquat trees like humidity levels between 50 and 60 percent but will do fairly well down to about 40 percent. To increase indoor humidity, especially during the winter months when forced-air heat can dry out the air, regularly mist the leaves of your tree. You also can place the container on a tray of pebbles filled with water, provided the bottom of the container isn’t actually touching the water. A cool-mist humidifier is another good way to optimize humidity levels.

Watering

Proper watering is essential for kumquat trees. The goal is to keep the soil lightly moist but not soggy. If the soil feels dry to the touch about 2 inches down, then it’s time to water until you see the water run out the bottom of the pot.

Soil

Kumquat tree survives well in almost any soil pH. But it can’t survive really sticky, clay-like soils that don’t drain readily. Ensure your soil easily drains away water. If you’re growing in a container, a citrus potting blend is great. Those growing directly in the ground should do a drainage test first.

To do a drainage test, dig a hole at least a foot deep, and fill it with water. If it empties out within about 20 minutes, your soil’s perfect. If the water stays in the hole for over an hour, it may be best to work through some compost or other drainage aid. Even a small amount of sand can improve drainage, but perlite is another good option.

Fertilizing

Apart from the cold winter months, kumquat plants need regular fertilizer. In spring, feed the plant with an all-purpose, slow-release citrus fertilizer. As the plant grows, give it diluted liquid fertilizer, like fish emulsion or liquid kelp on an occasional basis. Always water well before applying liquid fertilizers. Avoid getting fertilizer on the tree itself, aiming only at the surrounding soil.

Planting Instructions

You can successfully start a new kumquat plant by planting the seed in spring. Spring is the ideal time for kumquats as the temperature is pleasant with higher chances of rain and, of course, lots of sunshine. Early spring is also the best time to transplant a sapling kumquat.

Plant it in a place where there’s full sun. You can plant them in your backyard or outside on your patio in well-drained soil. They also do well in pots or containers with suitable drainage holes, but will grow much better if directly planted in the ground.

If you must grow them in a container, try an Air Pot, which is expertly-designed to cultivate a healthy root structure. Choose a location where your tree is protected from high wind conditions if possible.

It’s better to purchase a kumquat tree from a local nursery. Kumquat can sprout from seed, but the resulting plant is mostly weak. Choose a sunny spot and plant the tree in spring to ensure that the kumquat is well-established before winter arrives.

After choosing the spot, dig a hole at least 3-5 times wider than the root ball. Carefully place the tree into the hole and ensure that the soil is level with the ground. Tap down the soil for a smooth layer. Since kumquats need regular hydration, water the plant thoroughly and don’t let the soil become dry. Mist often, at least a few times a week, until the tree establishes.

Add organic mulch to the surrounding area, about 2-3 inches, keeping the mulch at least 10 inches from the trunk. Ensure proper watering and soil conditions for about a month and then fertilize. You can use a high-quality citrus formula to do this.

Kumquat tree, particularly the variety known as nagami kumquat, is relatively easy to grow. However, like other citrus trees, it can’t survive on neglect. When you’re planting the tree, it’s essential to treat it with a lot of care.

Pruning

Kumquat tree doesn’t require much pruning except when you have to remove dead or damaged branches that may be sucking up the tree’s resources. If you want to shape the tree, make sure to do so in winter before the spring flowering season and after harvesting the fruit.

Carry out an occasional pruning to open up the canopy can allow more light and airflow into the upper part of the tree. This helps with future flowering and reduces the chance of diseases taking hold.

Propagation

The trees aren’t generally grown from seeds, although they can be. The tricky part about seeds is that you won’t necessarily get an exact clone of their parent plant. If you’re trying to raise a particular cultivar, it’s best to go with another method.

Propagate instead by grafting young branches onto the rootstocks of grapefruits and oranges. The root systems of most grapefruit and orange trees are typically more resilient to fungal diseases in the soil.

Potting and Repotting Kumquat

Kumquat trees bloom best if their roots are slightly confined in the pot. Plan to repot every few years when the roots have clearly outgrown the container; choose a container just one size up. Any type of material can work for a container—plastic, metal, wood, ceramic, or clay.

Gently loosen the tree’s root ball from its old container, and replant it in fresh potting mix in the new container at the same depth as its previous pot. Ultimately, a fully mature indoor tree may require a 16- to 20-inch container, but a small plant will take several repottings over a decade or more before it requires such a large

Frost protection

Kumquat trees are more cold-tolerant than other citrus trees and can withstand 18°F (-8°C) of frost without injury. However, they still need some protection from freezing temperatures. If a frost is expected, cover the tree with a frost cloth or move potted trees indoors.

Pests and Diseases

Kumquat trees, like other citrus trees, can be susceptible to various pests and diseases. Here’s a list of some common issues to watch for:

• Citrus leafminer

The larvae of this small moth feed on young leaves, creating meandering tunnels or mines. This can cause leaf distortion and reduced tree vigor. Prune off infested leaves and use pheromone traps to reduce adult populations.

• Aphids

These small, soft-bodied insects feed on plant sap, causing leaf curling and distortion. They also excrete honeydew, which can lead to sooty mold. Spray the tree with water to dislodge aphids, or use insecticidal soap or neem oil.

• Scales

These small, flat insects suck sap from the plant, leading to yellowing leaves and poor growth. They also excrete honeydew, which can result in sooty mold. Scrape off scales with a brush, or use horticultural oil to smother them.

• Whiteflies

They are small, white, winged insects that feed on plant sap, causing leaves to become yellow and distorted. Like aphids, they excrete honeydew, which can lead to the growth of sooty mold. To control whiteflies, use yellow sticky traps to catch adult whiteflies. Spray your kumquat tree with water to dislodge the whiteflies. Apply insecticidal soap or horticultural oil, such as neem oil, to the affected areas.

• Spider mites

These tiny pests feed on plant sap, leading to the stippling and yellowing of leaves. Severe infestations can cause leaf drop and reduced tree vigor. Use water sprays to dislodge mites or apply miticides if necessary.

• Citrus canker

This bacterial disease causes raised, yellow lesions on leaves, stems, and fruit. In severe cases, it can lead to defoliation and fruit drop. Prune out infected branches and apply copper-based fungicides to prevent the spread.

• Citrus greening (Huanglongbing)

This serious bacterial disease is spread by the Asian citrus psyllid. It causes the yellowing of leaves, small, misshapen fruit, and tree decline. There is no cure for citrus greening, so prevention and control of the psyllid vector are crucial.

• Root rot

Caused by soil-borne fungi, root rot occurs in poorly drained soils and can lead to yellowing leaves, reduced growth, and tree decline. Plant kumquats in well-draining soil and avoid overwatering to prevent root rot.

To keep your kumquat tree healthy and pest-free, practice good cultural care, including proper watering, fertilization, and pruning. Monitor your tree regularly for signs of pests or diseases, and address issues promptly to prevent severe damage.

III. Kumquat Varieties

Like many citrus trees, the kumquat plant comes in numerous varieties.

• Nagami kumquat: Also known as Fortunella margarita or oval kumquat, most kumquats found in grocery stores are Nagami kumquats. The fruit has an oblong shape and very few seeds.
• Marumi kumquat: The Marumi kumquat is round in shape. It is larger than the Nagami kumquat and somewhat less sweet. This makes it good for marmalades but less ideal for eating whole or raw.
• Meiwa kumquat: Also called Fortunella crassifolia, the Meiwa kumquat is sweeter, larger, and juicier than the standard Nagami, but it tends to be more expensive and harder to find.
• Jiangsu kumquat: Also known as Fukushu kumquat or Fortunella obovata, this kumquat plant is distinguished by its round leaves. Its fruit is popular both in raw form and in marmalades.
• Hong Kong kumquat: Known scientifically as Fortunella hindsii, this wild kumquat grows natively in the forested hillsides of Hong Kong and southern China. Its fruit is quite small and bitter, so it functions best as an ornamental plant.
• Centennial Variegated kumquat: This kumquat variety grows more compactly than a typical Nagami kumquat tree (7 to 10 feet tall as opposed to 10 to 15 feet tall). Both its fruit and leaves feature variegated colors.
• Malayan kumquat: This kumquat from the Malay Peninsula is better known by its common name, hedge lime. The fruit is similar to a limequat, which is a genetic hybrid of a kumquat and key lime.

IV. Uses and Benefits

Kumquats are primarily grown for their edible fruits, which can be consumed fresh, candied, or used in marmalades, jams, and desserts. The fruit is also used in cocktails and savory dishes. In addition, kumquat trees are often grown as ornamental plants for their attractive appearance and fragrant flowers.

V. Harvesting and Storage

• Harvesting

The harvesting time for most varieties begins from November through January, while for others, it’s from December to April. The fruit is ripe when it’s slightly soft and deep orange. Pick the fruit using scissors or pruning snips to avoid damaging the plant. You can also trim the fruit along with a small piece of the branch.

• Storing

Kumquat fruits don’t have a long shelf life because they have thin, delicate peels. If you want to store them for a week or so, keep them in fully closed paper bags or plastic bags at room temperature. However, it’s best to store the fruit in the fridge.