Rambutan is occasionally only shrub-like, but is usually an evergreen tree with an open, spreading crown; it usually grows from 9 - 15 metres tall in the wild, though exceptionally can reach up to 44 metres, whilst cultivated forms are more commonly 4 -7 metres. The straight bole is usually around 40 - 60cm in diameter, exceptionally to 125cm with buttresses up to 400cm.
This is one of the most popular fruits of the tropics, the plant is widely cultivated in suitable climates around the world, both commercially and in gardens, for its edible fruit and also as an ornamental.
The plant also has a range of local medicinal uses and supplies dyes, oil and a useful timber.
The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species.

Known Hazards

The fruit wall contains a toxic saponin; cases of poisoning are known.

Habitat

Found in the lower or middle storey in different types of primary and secondary forest ranging from dryland to swamp.
Lowland humid forests.
Usually on alluvial sites and hillsides with clay to sandy soils; at elevations up to 1,200 metres.

Cultivation Status

Cultivated, Ornamental, Wild

Cultivation Details

Rambutan grows best in the lowland humid tropics at an elevation below 600 metres, though it can also be grown non-commercially up to 1,950 metres.
It grows best in areas where annual daytime temperatures are within the range 21 - 35°c, but can tolerate 10 - 42°c.
When dormant, a mature plant may survive temperatures down to about -1°c, but young growth does not tolerate any frost and will be severely damaged at 4°c.
Temperatures down to about 5 - 6°c will cause defoliation.
It prefers a mean annual rainfall in the range 2,000 - 3,000mm, but tolerates 1,400 - 4,000mm.
It prefers climates with all-year rain, but can tolerate up to 2 - 3 dry months.
Prefers a sunny position, though young trees appreciate the shelter and dappled shade of trees growing overhead.
Prefers a clay loam soil, though it can be grown in a wide range of soil types, even ones with poor drainage, so long as they are not waterlogged.
Requires a moist fertile acid soil rich in organic matter.
Requires shelter from drying winds.
Prefers a pH in the range 5 - 6.5, tolerating 4.5 - 7.5.
Seedling trees take 6 - 8 years to produce their first crop, whilst grafted trees can fruit in their second year.
Fruit yields increase for the next 8 - 10 years; the tree has an economic life of about 15 - 20 or even 30 years, whilst it might live for up to 60 years.
Trees usually fruit twice a year, yielding 1,000 - 1,500 fruits per tree per year at age 5 - 7 years and 5,000 - 6,000 fruits per tree for older trees.
Very good trees may yield up to 170 kilos per tree and yields per hectare may be from 2 - 20 tonnes.
The fruit travels well if packed properly, but shelf life is only a few days, mainly because the fruit loses weight rapidly and appendages and skin turn black. Keeping the fruits moist and shaded prolongs this period slightly.
There are many named varieties.
Trees are usually dioecious, but most commercial cultivars are females that also produce a few male flowers (up to 0.5%) and, with adequate bees and other pollinators present, these are sufficient for fertilization to occur.

Edible Uses

Fruit - raw or cooked.
The sweet, juicy, light-coloured flesh is delicious eaten raw.
The edible portion is the layer of white, melting, subacid pulp that surrounds the rather large seed.
Sour forms are often cooked - they can be stewed, canned in syrup, used in jams, jellies etc.
The bright red, ovoid fruit is 5 - 6cm long and is produced in clusters of 10 - 12 fruits.
Seed - occasionally roasted and eaten.
A bitter flavour, it is also said to have narcotic properties.
An oil or tallow similar to cacao butter, with a high level of arachidic acid, can be rendered from the seeds.

Medicinal

The green fruit is said to be astringent, stomachic, and anthelmintic.
It is used in the treatment of various diseases, especially fevers and diarrhoea.
The leaves are used in poultices for headaches.

The shell of the fruit contains tannins and is used as an astringent.
In Java, the toxic saponin found in the fruit wall is dried and used as medicine.
In Malaysia, the roots are used in a decoction for treating fever.
The bark is used as an astringent for tongue diseases.

Agroforestry Uses

Legumes with low growth habits, such as Canavalia, Crotalaria and Vigna, can be beneficially intercropped with rambutan.

Other Uses

The young shoots are used to produce a green colour on silk that is first dyed yellow with turmeric.
The fruit walls are used, together with tannin-rich parts of other plants, to dye silk black after a preliminary red staining.
The leaves are used, together with mud, as an impermanent black dye.
A red dye used in batik can be obtained from the leaves and fruit.
The seeds contain an oil that has been used for illumination and a fat that has been used to make soap.
The seed kernel can be used for the production of rambutan tallow, a solid fat similar to cacao butter, which is used for soap and candles.
The reddish coloured wood is liable to splitting during seasoning. It is moderately hard to very hard, strong and tough. It is easy to work and can be finished well. It is durable under cover and generally resistant to insect attacks, but susceptible to fungal attacks. Usually too small to be valued as timber.

Propagation

Seed - it has a very short viability and so needs to be sown as soon as it is extracted from the fruit.
Wash the seed first to remove traces of the fruit.
Sow the seed in containers or in a nursery seedbed in light shade - germination should take place in 7 - 20 days.
Properly cared for, the seedlings grow rapidly.
They quickly produce a large root system and so need to be planted out into their permanent positions when still young.
Layering.
Grafting.