Rambutan - Cultivation

Cultivation

Rambutan is adapted to warm tropical climates, around 22–30°, and is sensitive to temperatures below 10 °C. It is grown commercially within 12–15° of the equator. The tree grows well on heights up to 500 metres (1,600 ft) above sea-level and does best in deep soil; clay loam or sandy loam rich in organic matter, and thrive on hilly terrain as they require good drainage. Rambutan is propagated by grafting, air-layering, and budding; the latter is most common as trees grown from seed often produce sour fruit. Budded trees may fruit after 2–3 years with optimum production occurring after 8–10 years. Trees grown from seed bear after 5–6 years.

The aril is attached to the seed in some commercial cultivars, but "freestone" cultivars are available and in high demand. There is usually a single light brown seed, which is high in certain fats and oils (primarily oleic acid and arachidic acid) valuable to industry, and used in cooking and the manufacture of soap. Rambutan roots, bark, and leaves have various uses in medicine and in the production of dyes.

In some areas rambutan trees can bear fruit twice annually, once in late fall and early winter with a shorter season in late spring and early summer. In other areas like Costa Rica there is a single fruit season, with the start of the rainy season in April stimulating flowering and the fruit is usually ripe in August and September. The fragile nutritious fruit must ripen on the tree, then they are harvested over a four to seven week period. The fresh fruit are easily bruised and have a limited shelf life. An average tree may produce 5,000–6,000 or more fruit (60–70 kg or 130–155 lb per tree). Yields begin at 1.2 tonnes per hectare (0.5 tons/acre) in young orchards and may reach 20 tonnes per hectare (8 tons per acre) on mature trees. In Hawaii, 24 of 38 cultivated hectares (60 of 95 acres) were harvested producing 120 tonnes of fruit in 1997. It has been suggested that yields could be increased via improved orchard management, including pollination, and by planting high yielding compact cultivars.

Most commercial cultivars are hermaphroditic; cultivars that produce only functionally female flowers require the presence of male trees. Male trees are seldom found as vegetative selection has favored hermaphroditic clones that produce a high proportion of functionally female flowers and a much lower number of flowers that produce pollen. There are over 3,000 greenish-white flowers in male panicles, each with 5–7 anthers and a non-functional ovary. Male flowers have yellow nectaries and 5–7 stamens. There are about 500 greenish-yellow flowers in each hermaphroditic panicle. Each flower has six anthers, usually a bi-lobed stigma, and one ovule in each of its two sections (locules). The flowers are receptive for about one day but may persist if pollinators are excluded.

In Thailand, rambutan trees were first planted in Surat Thani in 1926 by the Chinese Malay Mr. K. Vong in Ban Na San. An annual rambutan fair is held during August harvest time.

In Malaysia, rambutan flowers from March to July and again between June and November, usually in response to rain following a dry period. Flowering periods differ for other localities. Most, but not all, flowers open early in the day. Up to 100 flowers in each female panicle may be open each day during peak bloom. Initial fruit set may approach 25% but a high level of abortion level contributes to a much lower level of production at harvest (1 to 3%). The fruit matures 15–18 weeks after flowering.

Rambutan cultivation in Sri Lanka mainly consists of small home gardens. Malwana, a village located in the Kelani River Valley, is popular for its rambutan orchards. Their production comes to market in the months of May, June and July, when it is very common to observe seasonal traders along the streets of Colombo. Sri Lanka also has some off-season rambutan production in the months of January and February in areas like Bibile, Medagama and Monaragala.

Both male and female flowers are faintly sweet scented and have functional nectaries at the ovary base. Female flowers produce 2–3 times more nectar than male flowers. Nectar sugar concentration ranges between 18% and 47% and is similar between the flower types. Rambutan is an important nectar source for bees in Malaysia.

Cross-pollination is a necessity because anther is absent in most functionally female flowers. Although apomixis may occur in some cultivars, research has shown that rambutan, like lychee, is dependent upon insects for pollination. In Malaysia, where only about one percent of the female flowers set fruit, research revealed that no fruit is set on bagged flowers while hand pollination resulted in 13 percent fruit set. These studies further suggest that pollinators may maintain a fidelity to either male or hermaphroditic flowers (trees), thus limiting pollination and fruit set under natural conditions where crossing between male and female flowers is required.