Kumquat: planting, cultivation and harvest

Botany

Kumquat is a charming citrus tree prized for its small oval fruits, sweet and tangy in flavour, eaten whole with skin. It has evergreen, glossy green foliage and scented white flowering. Kumquat is native to Asia, notably southern China, where it grows in humid forests. Cultivation spread long ago across other Southeast Asian countries: Malaysia, Hong Kong, Myanmar, Japan, Taiwan, Philippines…

Name kumquat comes from Cantonese gām-gwāt and means “golden orange”. It was introduced to Europe in 1846 by English botanist Robert Fortune (1812–1880), which explains scientific name Fortunella. However, recent studies place kumquats in genus Citrus, alongside lemon, mandarin and orange trees.

Kumquat is one of most hardy citrus trees: capable of tolerating down to –10 °C, but its fruits are very sensitive to cold. Especially as fruits appear in autumn–winter. To enjoy them, better move bush under cover for winter.

Fortunella japonica (W. Fitch – Wellcome Collection)

Kumquat belongs to botanical family of citrus trees, Rutaceae, which comprises 1,730 species. Rue, Ruta graveolens, gave its name to this family. Rutaceae generally have aromatic glands in their tissues that contain essential oils, which explains why many of these plants have scented foliage. Likewise, their flowering is often fragrant, while fruits have pronounced, tangy flavour (citrus) or spicy taste (Zanthoxylum). Many plants in this family contain essential oils in their tissues. Ornamental plants such as Choisya or Skimmia also belong to this family.

Today, kumquat is cultivated in Asia, Florida, Greece (notably on island of Corfu) and southern France. Most common in cultivation are Fortunella margarita, Fortunella japonica and Fortunella obovata. Cross-breeding of kumquat with other citrus trees has produced new varieties, such as calamondin (cross between kumquat and mandarin), limequat (cross with lemon), or orangequat (cross with orange).

Kumquat grows slowly and forms a bush with a rather rounded habit. It can reach up to 4 metres in height. However, in cultivation, especially in a pot, it rarely exceeds 2 metres. Branches sometimes bear thorns.

Kumquat generally flowers in spring, between April and June–July. Flowers are attractive, small and simply shaped, and are also appreciated for their scent. They consist of five white petals surrounding a cluster of stamens (male organs, producing pollen), with a pistil (female organ, receiving pollen) at centre. Flowers may be solitary or gathered in small axillary cymes.

This is a melliferous flowering, appreciated by bees. Bees forage nectar from the flowers and at the same time ensure pollination.

White, fragrant kumquat flowers (photos: Frank Vincentz / Thanh Nam Nguyen)

Leaves are entire, ovate and measure 4 to 10 cm in length. They are dark green and glossy, paler beneath. Leaves are fairly thick and leathery, characteristic of citrus leaves. They are arranged alternately on stems. Leaves bear aromatic glands that contain essential oils.

Leaves are evergreen, remaining on the bush all year round.

Between November and January (sometimes until March), Kumquat produces small oval, bright orange fruits measuring 3 to 5 cm in length. Fruits are eaten as a snack whole, with skin, which is thin and entirely edible. They have a pleasant tangy flavour. Usually eaten raw but can also be cooked. Fruits can remain on bush for a long time before falling. Like citrus foliage, fruits also contain essential oils. Kumquat fruits are sensitive to cold and may freeze once temperatures reach –4 °C. A mature kumquat can produce hundreds of fruits each year. Fruits tend to be more spherical in Fortunella japonica, and more oval in Fortunella margarita.

Small orange kumquat fruits

Main varieties of Kumquat

Most popular varieties

Kumquat Nagami - Fortunella margarita

One of the most widely grown varieties! It is fairly vigorous and produces abundant fruit. Its fruits are ovate, slightly elongated, with a mildly acidic flavour.

• Flowering time July to September
• Height at maturity 2,50 m

See the product sheet

Marumi Kumquat - Fortunella japonica

Derived from species Fortunella japonica, the fruits of this kumquat are round, with a soft, sweet bark, while the flesh is tart. Leaves are also a little more rounded than those of other kumquats.

• Flowering time July to September
• Height at maturity 2,50 m

See the product sheet

Kumquat Fukushu - Fortunella obovata

This kumquat is less well known and less commonly cultivated than other varieties. Its fruits are slightly more acidic, but the fruit's bark remains relatively soft and sweet. Leaves have a fairly rounded shape.

• Flowering time July to September
• Height at maturity 2,50 m

See the product sheet

Planting

Where to plant?

Kumquat tolerates down to -10°C and is one of the hardiest citrus trees. However, its fruit are more sensitive to frost than the bush itself, and from -4°C its fruiting (which occurs in winter) may be compromised! Reserve planting in ground for mildest regions (south of France, Corsica). Elsewhere, best to plant in a pot and bring under cover for winter! Also avoid growing it all year inside a house or flat, as atmosphere would be too warm and dry.

Choose a sunny, fairly warm spot where it will benefit from plenty of light. However, if you live in the south of France, it is preferable that kumquat is sheltered from sun during hottest hours to avoid scorching the leaves. Conversely, in the northern half of the country, do not hesitate to place it in full sun! For example, it will thrive at foot of a south-facing wall. We also recommend choosing for kumquat a spot sheltered from wind.

Kumquat likes light, free-draining soil where water does not stagnate. Whether planted in ground or in a pot, it is generally best to add some coarse sand to planting substrate. A heavy feeder, kumquat needs rich, fertile soil. It is preferable to add well-rotted compost at planting time and, during culture, to apply some fertiliser. Grown in a poor substrate, it may become deficient, which could cause leaf yellowing or prevent fruit production. It prefers soils with neutral or acid pH, but — like many citrus trees — dislikes calcareous substrates.

When to plant?

Plant kumquat in spring, from April.

How to plant?

For planting in a pot:

1. Take a large container. You can for example choose a terracotta pot or a wooden trough. Important that base is pierced to allow drainage of watering.
2. Place a layer of clay pebbles or gravel at bottom, a few centimetres thick, to ensure effective drainage.
3. Fill with substrate, ideally a mix of potting compost, well-rotted compost and coarse sand. You can also add a fertiliser for citrus trees.
4. Plant your kumquat in the pot.
5. Replace soil around, but take care not to bury the collar!
6. Water generously.

For planting in ground:

1. Dig a planting hole two to three times size of rootball.
2. Place in bottom a mix of potting compost, well-rotted compost and coarse sand. Do not hesitate to also add a fertiliser for citrus trees.
3. Plant kumquat.
4. Backfill planting hole around the bush.
5. Water generously.

Do not hesitate to spread a layer of mulch (leaf litter, wood chips, BRF…) around your kumquat: this will help retain soil moisture while limiting weed growth. Moreover, in winter mulch provides additional protection against cold! Finally, as it decomposes, mulch enriches soil with organic matter.

Fortunella japonica (photo Krzysztof Golik)

Care

Pot culture

Water regularly from spring to autumn, providing water as soon as potting compost surface feels dry (waterings once or twice a week). We recommend using rainwater rather than tap water. In all cases avoid leaving water to stagnate in the saucer. A good tip is to place some gravel in the saucer to raise the pot slightly, preventing the pot base from sitting in excess irrigation water. As kumquat is a bush that is greedy for mineral elements, make regular liquid feedings, for example once a month. You can also use slow-release fertiliser. In winter, reduce water and feedings.

Unless you live in Mediterranean region, kumquat must be protected from cold in winter… otherwise you are unlikely to enjoy its fruit! In autumn, around October, bring it inside to a frost-free shelter, for example into an unheated greenhouse or a conservatory. Choose a bright but unheated spot: ideal temperature is between 7 and 10 °C. In spring, from May onwards, move kumquat outdoors to a sunny position.

For more information, discover our tips to overwinter citrus trees.

Repot kumquat on average every two years, preferably in spring. This will give kumquat more room by placing it in a slightly larger pot while renewing its potting compost. In years when you do not repot, perform a top-dressing: remove surface substrate a few centimetres deep and replace with fresh potting compost.

You can prune kumquat in spring. This helps give a more balanced, compact and ramified habit while limiting its development. It also improves air and light penetration to the centre of the bush. Prioritise removal of dead or damaged branches and those that seem badly placed. You can also remove some branches from the centre to open up the foliage.

When under cover, kumquat can be attacked by scale insects (notably mealybugs). They are visible as small whitish, cottony clusters. They weaken the bush and can lead to development of sooty mould (a fungus characterised by a black deposit on leaves). To remove scale insects, use a cloth soaked in 90% alcohol, black soap and vegetable oil. Kumquat can also be attacked by red spider mites. As they particularly favour dry atmospheres, you can easily get rid of them by spraying water onto the foliage… they hate humidity! Finally, aphids can also cause problems. These small insects settle on stems or leaves and extract sap, which weakens the plant and can lead to sooty mould. To eliminate them, spray foliage with a solution of black soap diluted in water.

Outdoor cultivation

If you have planted your citrus tree outdoors, remember to water regularly, at least during the first year, then later during dry spells, preferably using rainwater. Also add organic fertiliser or well-rotted compost to feed the bush. It is also preferable to mulch around the base with dead leaves, pine bark or ramial chipped wood, as this helps keep soil cool for longer while limiting weed growth.

In autumn, when temperatures fall, you can use horticultural fleece. This mainly protects the fruit, which are fairly frost-sensitive, while the bush can tolerate down to −10 °C.

Harvest and consumption

Fruits are generally harvested between November and January, sometimes as late as March, depending on varieties and growing conditions. When ripe, they develop a lovely orange colour and come away easily. They can naturally remain on the bush for a very long time before falling (they become progressively sweeter… but over time they may lose flavour! It’s therefore better to harvest them beforehand). Conversely, before ripeness, fruits taste bitter.

When ripe, kumquats have a fairly sweet, sugary and tangy flavour. As with most citrus trees, their fruits are rich in vitamin C. They contain relatively few pips. They are usually eaten raw, as they are, their small size making them perfect for snacking at any time of day! Unlike other citrus trees, kumquats are eaten with their skin, which is quite sweet and thin. Kumquats can also be cooked, used in jam, marmalade or chutney… They can also be candied or made into sorbets. They can also simply be used to decorate desserts and cakes. They accompany savoury dishes (tagines…), or are used in sweet-and-sour sauces, for example in Asian dishes.

Fortunella hindsii

Multiplication

Sowing

Sowing is carried out in spring, preferably using fresh seeds. Best is to use seeds collected from a ripe kumquat intended for eating. Rinse seeds but do not let them dry.

1. Take a pot and fill it with special seed-sowing compost.
2. Sow seeds, then cover with a layer of compost about 1 cm thick.
3. Firm down lightly.
4. Water with a fine spray.
5. Place pot in a bright spot at a temperature between 19 and 24 °C.

Ensure substrate remains slightly moist until germination.

It will take several years before kumquat begins to produce fruit.

Grafting

Grafting of kumquat is carried out in spring from May to take advantage of fairly mild temperatures. A shield graft is performed.

As rootstock, Poncirus trifoliata is generally used, a thorny citrus that has the advantage of being robust and very hardy. It is also possible to graft kumquat onto bitter orange.

Propagation by cuttings

Kumquat is propagated by cuttings in summer, around August until early September.

1. Take a segment of stem about 15 cm long, cutting just before a node (point where leaves attach to the branch). Make a clean cut using a sharp, disinfected knife.
2. Remove leaves at base of the cutting, leaving only a few at top of the stem.
3. Prepare a pot with a mix of compost and coarse sand, and water to moisten.
4. Plant base of the stem into the substrate and firm well around it.
5. Place a clear bag or a plastic bottle over the pot to create a humid atmosphere (cutting under cover).
6. Place pot in a bright spot, out of direct sunlight.
7. Ensure substrate remains slightly moist, and occasionally air the cutting to prevent rotting.

Association

In the garden, kumquat can find a place alongside other fruit and unusual bushes. Discover for example Asimina (pawpaw), Feijoa, Japanese goumi or Zanthoxylum! Some citrus trees are relatively hardy: mandarin ‘Satsuma’ or bitter orange, which seem able to withstand −10 °C. You can also enjoy unusual fruits of the strawberry tree.

For more ideas and inspiration, discover Ingrid’s article on our blog: “7 exotic, hardy fruit trees to grow in the garden”

In the south of France, it will feature in a Mediterranean-style garden! Pair it with oleanders, bougainvilleas, lavender, olive tree, santolina… These low-maintenance plants enjoy full sun and tolerate poor, dry soils well. They will need little maintenance! Also enjoy originality of euphorbias and colourful flowering of rockroses.

If you live in a cooler area, you can still create this southern feel. Grow kumquat in a pot and, from spring to autumn, place it on your terrace or another sunny spot among Mediterranean-style plants.

Use kumquat to create a Mediterranean ambience. Fortunella margarita, lavender, oleander (photo Challiyan), rockrose ‘Ben Fhada’ and olive tree

You can also plant it on its own, or simply plant a few perennials at its base, such as grasses. This will give it room to develop well, and its foliage will not be hindered by shade from other trees or bushes.