Lychee

Lychees are widely grown between 10^o and 25^o latitude at lower elevations, particularly in Asia. The lychee is slow growing, reaching 30 to 100 feet in the tropics, but only 20 to 30 feet in California. The fruit resembles a reddish brown golf ball. (The fruit is red when fresh.) The eggshell-like covering contains within a translucent flesh (aril) that is similar to a grape with a sweet, subacid flavor. The aril surrounds a single (usually) large brown seed. The fruits are available fresh, frozen, canned and dried. That lychees are highly prized can be appreciated by the fact that emperors residing in northern China had bearing trees dug and transported so that ripened fruit would be available upon arrival. The juvenile lychee is very frost sensitive; however, once established it can survive low temperatures about as well as cherimoyas, temperatures that will severely damage such tropicals as mango and banana. Lychees have very finicky fruiting habits, particularly when removed from their native habitat. Propagation is costly since marcottage or approach grafting must be used. A market demand exists in the Asian community for the fresh fruit which is available only in limited quantities from south Florida in late June and early July.

Botany

The soapberry family, Sapindaceae, includes about 2,000 tropical and temperate species. The most infamous American member is the akee (Blighia sapida). Even though the fruit is poisonous when underripe or overripe, it is commonly used in cooking in the West Indies. The other American member of note, the mamoncillo, Spanish lime or genip (Melicocca bijuga)is more like the lychee. Little commercial attention has been paid to it since the fruit is normally too acidic and the edible pulp is minimal. Some superior selections have been made in Florida and Puerto Rico.

The fruits that are more closely related to the lychee have received far more attention. The longan, (Dimocarpus longan, sometimes known as Euphoria or Nephelium longana), is the more temperate zone relative. The fruit is easily distinguished from the lychee in that it is smaller and the shell is tan and smooth. The fruit flavor is more musky and less sweet. The fruit is esteemed by many Chinese, particularly in areas that are too cold for the lychee. A more tropical relative is the rambutan (Nephelium lappaceum). Its fruit is very similar to the lychee in size and shape except the outer shell protuberances end in hair-like structures, hence the rambutan is often called the hairy lychee. More tropical yet is the pulasan, (Nephelium mutable), which also tastes much like a lychee. It grows only in areas similar to its homeland of Borneo.

In California the lychee tree grows to about 20 to 30 feet. The tree is dense and as wide as it is tall. Its leaves are alternately pinnate, with 4 to 8 oblong, lanceolate, 2 to 3 inch leaflets. Marcots can start to bear in 3 to 5 years. It produces 3 types of small white flowers; male which are usually first, hermaphrodite fruiting as males, and hermaphrodite fruiting as female. Although the lychee is self-fruitful, it is capricious. Many techniques are employed to induce fruiting including girdling, withholding fertilization until after fruit sets, withholding water, and other techniques that will produce sufficient stress to induce fruiting. Fruits, borne in large clusters, ripen in California over a 3 to 4 week period between June and November, (the variation in ripening is primarily dependent on the area in which they are planted). The 1 to 1.5 inch ovoid fruits vary in color from brownish red to amber. The skin (called a shell) is tough with small protuberances. The shell is easily peeled from the grape-like aril. In better varieties the aril separates easily from the seed and the aril to seed ratio is high (about 80%). The fruits are often dried.

Climatic requirements

The lychee needs to be protected from frost until it is well established (about 3 years). Mature trees are much less sensitive and can survive temperatures as low as 26 degrees F for short periods of time. Lychees are native to Kwangtung and Fukien provinces of China where the winters are dry and the summers hot and very humid. This is the climate they require in order to set fruit readily. Although tropical in nature, lychees do need a seasonal variation in temperature to produce fruit. The chilling requirement is estimated to be about 100 to 200 hours between 32^o and 45^o F.

Soil Requirements

The lychee grows well on soil types ranging from sandy to clay. It prefers a pH of between 6 and 7.5. There is some evidence in California that clay soils can lead to root disease problems. Water logging definitely will cause problems.

Cultural Requirements

Spacing and training

Trees in California have been planted on 20 to 30 foot centers. Wind protection is advisable.

Watering

The lychee has a high water demand that must be met. Therefore, since the lychee has a very shallow root system, surface mulches should be used in hot, dry conditions. To encourage fruiting, water should be withheld 6 to 8 weeks before flower set; however, in hot, dry conditions, water may have to be judiciously applied. Too much water after fruit set can cause the fruit to be aborted. Therefore, watering needs to be increased gradually after fruit set.

Fertilization

Young trees are very susceptible to fertilizer burn at all ages, fertilizers should be avoided when the tree is in flush until the flush hardens. To encourage fruiting, no fertilizer should be applied after the last flush. Although fertilizer compositions and timing are very important in achieving fruiting, recommendations for composition vary greatly. Mature trees are heavy feeders suggesting that a good supply of nitrogen is necessary. Further, since chlorosis can be a problem, fertilizers with acidic reactions may be necessary and the use of chelates may even be necessary.

Pruning

Young trees up to 3 or 4 years are headed back 3 or 4 inches to produce a more dense tree. Older trees require minimal pruning because branches are clipped off when clusters of fruits are harvested and this induces the new growth that is necessary to produce the next crop. From this, one infers that if fruiting does not take place in a given year, tip pruning could be useful in inducing a crop the following year. Branches are sometimes girdled in the fall to induce better flowering and fruiting. On average, over two years, no more than half the tree limbs are girdled per season. An extreme example would be girdling all limbs every other year.

Pests and Diseases

Not much is known about pests or diseases in California. Elsewhere, one of the most serious pests is the leaf curl mite, (Aceria lychee). Others include the citrus aphid (Toxoptera aurantii) and the red spider mite (Paratetranychus hawaiiensis). Nematodes are also a potential problem.

Propagation

Since seedlings are extremely variable with regard to fruiting, clonal propagation, specifically marcottage (air layering), is almost universally used. Cuttings can be struck, but not easily. Grafting and budding are difficult at best. Approach grafting is sometimes used instead of marcottage.

Marcottage is practiced from spring to fall. Roots usually develop in 8 to 10 weeks. Hardening the marcot is critical. After removal from the tree, about half of the leaves are removed, and the marcots are placed in an area with controlled humidity until the roots are established. Trees are planted out the next season

Harvesting and Storage

Fruit is harvested in clusters. Individual fruits can clipped off later and packed in polyethylene bags. The denseness of the lycheee tree does not lend itself to the use of ladders, and fruit clusters are harvested with pruning poles. Partially ripe fruits can not be ripened after picking

Fruit can be stored at 30^o to 45^o F for up to 3 months; however, the bright red color turns brown in about 10 days. Ethylene dibromide fumigation does not effect the quality of the fruits.

Fiscal

Undetermined.

Market

Potential market acceptability of lychees is high since the fruit is well accepted in areas where it is available. A demand already exists in Asian markets which sell whole, frozen, unshelled lychees in lieu of the fresh product.

Compiled by Robert Vieth, Master Gardener