Longan – Dimorcarpus longan
Longan is known as the “little brother of lychee” It is noted not only for its nutritious and sweet fruit but also for its ornamental appeal.
The longan tree grows up to 40 m tall. Its trunk reaches a diameter of 1 m , although some specieds are considered creeping shrubs. The branches are cylindrical and sometimes have horny projection on the bark.
The leaves are densely hairy and occur in two to six pairs. The flower cluster is long and borne at the end of the shoot. It has small and yellow to brown flowers.
The fruits grows in lose clusters. It is round to egg-shaped, yellow to brown, and smooth or rough in texture. The edible pulp which encloses the seed is sweet, thin, and translucent white. The seed is round with a shiny blackish brown coating.
The fruit is eaten fresh and contains proteins, carbohydrates, minerals, vitamins, and fats. It can be canned and prepared in its own juice with little or no sugar. The dried flesh is prepared as a refreshing drink. The flesh can be macerated in alcohol to produce liquor.
The seeds that contain saponin can be used as shampoo. The seed, fruit flesh, leaves, and flowers have several medicinal uses.
Soil and climatic requirements
Longan thrives one rich sandy loam soil, rocky limestone, or in river banks. However, they grow satisfactorily in deep, fertile, and clay loam soils with a high water table.
This subtropical tree grows well in the tropics with a mean temperature of 15-22 degrees Celsius during flowering. Night temperatures, however, should not be warmer than 20-25 degrees Celsius. Areas with an annual rainfall of 1,500-2,000 m are preferred.
Propagation. Propagate longan by air layering and approach grafting. Use seedlings of the same cultivar as roostock. Air layers root in two to two and a half months during the rainy season. Nurse seedlings in the shade for 6-12 months after separation from the mother plant.
Planting. Plant the trees with a space ranging from 6 m x 6 m – 12 m x 12 m. For orchards, the trees may be spaced 10 m x 10 m in a square pattern.
Irrigation. Provide longan with ample moisture from flowering until shortly before harvesting. Apply mulch and supplement irrigation during this period.
Fertilization. Apply fertilizer once the young trees have become established and have produce their first growth flush. For bearing trees, apply 0.4 kg of complete fertilizer (14-14-14) per tree per year, 40% at fuit set and 60% after fruiting. Avoid application of fertilizer prior to flowering time. It is also a good idea to do regular light applications of poultry manure to the mulch.
Pruning. Prune young trees to limit the number of main branches. Cut off some of the unproductive twigs soon after harvest. Remove twigs that are least likely to fruit the following year.
Pest and diseases. The common pests that attack longan are the stink bugs, caterpillar, piercing months, and fruit flies. Control the damage of stink bugs with a parasite. Prevent the damage on fruits by bagging the panicles with plastic or paper bags.
An important disease that attack longan is rosette shoot or witches broom. To control this, cut the addected trees and burn them. Other important diseases include thread blight and powdery mildew.
Harvesting and Postharvest handling
Harvest only ripe fruits since harvested unripe fruits do not ripen anymore. Sample a few fruits for sweetness before harvesting the rest. Ripe fruits have a dark, smooth skin, and sweet flesh. Pick fruits twice at an interval of seven to ten days.
Cut the whole panicle with a knife or scissors and do not drop it. Sort the fruits and bunch them.
Pack longan fruits in bamboo baskets with stalks intact. Line baskets with longan leaves. If the fruits are for export, detach them from the panicles and pack them in corrugated boxes or plastic baskets. Store at 5 degrees Celsius for 40-45 days and at 10 degrees celcius for 20 days. Fumigate with sulfur dioxide (SO2) for long term storage.
Source: PROSEA Leaflet no. 26