Growing Starfruit: Averrhoa carambola

Botanical Overview

A member of the Wood Sorrel family (Oxalidaceae), the Averrhoa genus contains two species, both cultivated for edible fruit. Averrhoa carambola, known as Starfruit, is more cold-hardy.

Description

Form: Short trunked, multi-branched tree.

Lifespan: 25-50 years.

Leaf retention: Evergreen in regions without freezes. Deciduous in low, near freezing temperatures.

Growth rate: Slow.

Mature Size: 20-30' (6-9m) high and as wide.

Flowers: Small, pink to purple, five petals, clustered, fragrant, edible.

Bloom: 2-4 times a year in regions without freezes.

Self-fruitful: Depends on cultivar.

Years before fruiting: 1-4 if grafted, 3-5 from seed.

Fruit: Yellow, waxy skin, usually five longitudinal ribs (can be 4-8), star-shaped cross section, edible. Dark yellow, translucent, juicy flesh with 0-12 flat, thin, edible seeds. The flavor varies from very sour (high oxalic acid) to slightly sweet.

Months for fruit to ripen: 2-3. The fruit are ripe when fully colored and rib edges are beginning to turn brown. The highest sugar content occurs on tree-ripened fruit. Fruit ripen very slowly off the tree and do not add sugar.

Storage after harvest: One week at room temperature.

Leaves: Green, grouped as 5-11 leaflets, tend to fold at night or when touched, edible.

Stems: No thorns.

Roots: In high pH soils, this plant should be grafted onto a suitable rootstock such as 'Golden Star'.

Cultivars of Note:

'Fwang Tung' Medium to large fruit, sweet, very good flavor, self pollinating, from Thailand.

'Kari' Medium to large fruit, sweet, very good flavor, self pollinating, from Hawaii.

Wildlife: The flowers attract bees and other insects.

Toxic / Danger: The fruit contains oxalic acid which can be dangerous for those with kidney disease.

Origin: Southeast Asia.

Cultivation and Uses

USDA hardiness zones: 10-13. Protect from freezing temperatures when young. Young plants can be killed at 32°F (0°C). Mature trees can withstand 27°F (-2.8°C) for short periods of time.

Chill hours: None.

Heat tolerant: All day part shade and extra water are needed above 95°F (35°C).

Drought tolerant: Increases with age from none to slight.

Sun: Full sun to part shade.

Planting: In regions with summer temperatures over 95°F (35°C), locate this tree in an area that receives part shade all day, especially afternoon shade. While full sun is normally recommended for better growth rate and fruiting, this plant cannot tolerate full sun in high temperatures. It must be protected from wind in order to prevent excess moisture loss and to prevent toppling. Dwarf varieties can be grown in containers.

Soil: This plant needs soil that is well draining, but it is generally tolerant of soil types. It performs best in pH 4.5-7.0 (strongly acidic to neutral), but can tolerate pH 7.1-7.8 (slightly alkaline) soil, although it will suffer iron, magnesium and manganese deficiencies. It is not salt tolerant.

Fertilize: Apply two applications of organic fertilizer a year. Apply plant micronutrients in irrigation water 2-4 times a year. If chlorosis occurs in winter, it will often disappear on its own in warmer weather.

Water after becoming established: Deep water twice a week, even in the winter. Avoid having the soil dry out entirely. Leaves that are wilting, folding, turning yellow and brown, and leaf drop are signs of insufficient water. This tree can withstand flooding for 2-10 days, but the soil must not stay waterlogged.

Mulch: Spread organic mulch under the canopy and 8" (21cm) from the trunk to reduce moisture loss and lessen root area temperature extremes.

First Three Years Care: Protect from freezing temperatures.

Prune: Prune to shape and size in mid winter. Flowers occur on both old and new wood.

Litter: Low except for unharvested fruit or dropped leaves in cold temperatures.

Propagation: Buds or shoots can be grafted onto hardy rootstock such as 'Golden Star' which performs better in high pH soils. Seed from ripe, fresh fruit can be used to grow this plant, although the seedlings are not true to their parents. Dried seed is not viable.

Uses: Ornamental, edible fruit. The fruit are often eaten raw but can be cooked. Peeling off the "wing" edges removes most of the oxalic acid.

Comments

Another common name for this species is Carambola tree.

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