Star fruit (Averrhoa carambola L.) also known as carambola, bilimbi and five-finger, is a tropical plant native to Southeast Asia. Star fruits have been cultivated in many tropical and subtropical areas such as Sri Lanka, Indonesia and Malaysia. Star fruit was introduced to Florida over 100 years ago. The first trees planted in Florida had tart fruit but then seeds and vegetative material from Thailand, Taiwan, and Malaysia have been imported to the United States that were sweet. In the US, star fruit is grown commercially in Southern Florida and Hawaii. Commercial growers can be found in Dade, Lee, Broward, and Palm Beach counties.
Note: Star fruit should be avoided to eat if you have been diagnosed with kidney disease because the fruit may contain enough oxalic acid to cause a rapid decline in renal function.
Star fruit is a tropical tree and grow in warm and hot temperatures. Although they can grow in subtropical areas that experience only occasional freezing temperatures. The best temperature to grow star fruit is 68° to 95°F, and the temperature below 65°F slows down the growth. The tree can tolerate short-term freezing, but large branches and mature trees may be killed at temperatures of 20° to 24°F. Temperature of 30° to 32°F may kill young leaves, young trees, and twigs.
Star fruit can be cultivated in southeastern and southwestern Florida as this area have warm to hot temperature as well as enough soil moisture. In central and northern Florida, star fruit should be protected in winter to avoid sever freezing.
Flowering and Pollination
Flowers are perfect, meaning both male and female reproductive structures are present. They are pink or purple. Although some star fruit varieties require cross pollination, most of them can produce many fruits without requiring a different variety for pollination. The varieties such as ‘B-10’ and ‘B-17’ produce more fruit when cross pollinated with another variety.
There are two types of star fruit; tart and sweet. Sweet varieties are usually recommended for fresh fruit while both sweet and tart can be used for processing or fresh fruit.
Soil and Fertilizer requirements
Star fruit needs well-drained soil, continuous access to soil moisture, and protection from wind. They grow best in neutral or slightly acidic soil (pH 4.5 to 7).
The tree cannot tolerate drought and as low soil moisture results in appearing of drought symptoms such as leaf folding, leaf wilting, yellowing and browning of leaves, leaf drop, reduced flowering and fruit size, stem and limb dieback, and in severe drought, tree death. In contrast, they can tolerate flooding for about 2-10 days.
It is recommended to apply ¼ to ½ pound of a mixed fertilizer containing nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) to the young trees every 30 to 60 days. When trees become mature, you can increase fertilizer rate to 1 to 5 labs with an application frequency of 4 to 6 times per year.
Star fruit trees usually are grafted on seedling rootstocks. Veneer grafting and chip budding are two methods of grafting that give a good result, especially when applied on actively growing trees. In a desirable environment, star fruit may start producing fruit within 10 to 14 months after planting.
Star fruit trees should be planted at least 0 to 30 feet or more (7.6 to 9.1 m) away from buildings and other trees, otherwise they may not produce much fruit due to shading.
Pest and disease
Several pest and disease may attack star fruit and damage the trees. Scales such as plumose (Organelle longispina) and philephedra (Phil ephedra tuberculosa) may attacked to the leaves and twigs and causing defoliation and stem dieback. The diaprepes weevil (Diaprepes abbreviatus) causes damage to the roots, which may lead to root and shoot dieback.
Stink and squash bugs also damage fruits making small holes on fruits that may lead to infection by fungi which cause soft rot of the fruit. Other insects such as Fruit blotch miner, Brown scales, red-banded thrips, and red-banded thrips have been observed damaging the fruits. Birds, opossums, and raccoons may also damage fruits.
Various fungi may attack star fruit and cause damage. They may leave reddish colored leaf spots especially on older leaves or trees that are under stress. The control of these fungi is not necessary as the damage is minor. Root rot caused by fungus Pythium splendens may lead to general decline of the trees with the symptoms including loss of tree vigor, leaf drop, twig, shoot, and root dieback, and reduced fruit size and production. For more information and control measures, consult your local UF/IFAS Extension agricultural agent.
More Information: https://edis.ifas.ufl.edu/publication/MG269