Syzygium jambos

Rose apple (Syzygium jambos)
Scientific name	Syzygium jambos (L.) Alston
Genus	Syzygium
Family	Myrtaceae
Order	Myrtales
Fruit type	Fleshy berry
Growth form	Evergreen tree
Climate and hardiness	USDA zones 9 to 11; zone 9 is marginal
Mature height	7.5 to 12 m (25 to 40 ft) in ground
Mature width	Crown often wider than it is tall
Growth rate	Slow as seedlings, speeds up once established
Soil	Adaptable; prefers deep, moist soil and tolerates wet feet
Water	Regular moisture; tolerates seasonal dryness
Sun	Full sun once established. Young trees want partial shade.
Germination	10 to 120 days from fresh seed; sow fresh
Years to fruit	About 3 to 4 years from seed
Pollination	Self-fertile. Bees and other insects do the work.
Yield	Modest; about 2 kg per mature tree per season
Harvest	Dry-season bloom; fruit early in the wet season

Rose apple (Syzygium jambos; also Malabar plum, pomarrosa, jambu mawar, yambo) is a Southeast Asian tree in the genus Syzygium and family Myrtaceae, grown for its showy rose-scented flowers and crisp, aromatic fruit. The fruit is hollow, with 1 to 4 seeds rattling loose in the center, and so perishable it rarely makes it to market. Native to Malaya and the East Indies, it is now naturalized across the tropics.^[1]

Description

New foliage flushes rosy pink before maturing to glossy dark green. Photo by Tonton Bernardo, CC BY-SA 3.0, via Wikimedia Commons.

The common name "rose apple" is used for several Syzygium species. S. jambos can be recognized by the following combination of features:^[1][2]

• Lanceolate leaves 10 to 22 cm long, opposite, new flush rosy pink
• Big creamy-white flower puffs 5 to 10 cm across, made almost entirely of about 300 stamens
• Nearly round to slightly pear-shaped fruit, 4 to 5 cm, pale yellow to whitish skin, often pink-blushed, loose seeds rattling in a hollow center

• Rosewater scent when you rub or bite a ripe fruit

The species is usually a low-branching evergreen tree or large shrub, commonly 3 to 15 m tall. The bark is dark brown and fairly smooth, and the young twigs and mature leaves are glabrous. New leaves emerge reddish or rosy pink before turning glossy dark green. The leaves are lanceolate, generally 10 to 20 cm long, with a pointed tip and a short, inconspicuous petiole.^[1][2]

Flowers are produced in small terminal clusters on new growth. They are white to greenish white, and the numerous long stamens give each flower its conspicuous, powder-puff appearance. The flowers may be fragrant, but the strength of the scent varies. The ripe fruit is more consistently aromatic, with a strong floral or rosewater bouquet that accounts for the common name.^[1]

The fruit is thin-skinned, waxy, and usually 4 to 5 cm across. Its crisp, watery flesh surrounds a slightly fluffy hollow rather than the firm seed mass found in guava. One or two large, smooth seeds commonly lie loose in the cavity, although fruit may contain more. Shaking a ripe fruit can produce the characteristic rattle of the loose seeds. Fruit color ranges from pale yellow or greenish white to pink-blushed, and the skin bruises readily after harvest.^[1][2]

Most often confused with:

• Wax apple (S. samarangense): larger, glossy red or pink bell-shaped fruit, no rose scent
• Malay apple (S. malaccense): much bigger, deep red fruit
• Java plum (S. cumini): dark purple, astringent
• Watery rose apple (S. aqueum): pear-shaped, without the rose aroma

The rosewater scent of the ripe fruit is a useful field characteristic, but it should be considered alongside the leaf, flower, and fruit characters above.

Climate and site

Mature tree habit, showing the dense crown and wide-spreading branches. Hana Highway, Maui. Photo by Forest & Kim Starr, CC BY 3.0, via Wikimedia Commons.

A true tropical that can be grown in warm subtropical areas. It is generally listed for USDA zones 9 to 11, although zone 9 is marginal. The tree may survive with protection, but regular freezes usually prevent fruiting. At the cool edge of its range, including coastal California and San Francisco, it can grow vigorously without setting fruit. It flourishes with daytime temperatures of 18 to 38 °C, tolerates 5 to 40 °C, and grows from sea level to about 1,200 m in the tropics (2,300 m in Ecuador). Above those elevations, fruiting becomes unreliable.^[2][3][6]

Provide regular moisture. In the wild it is commonly found along streams and can tolerate wetter soils than many fruit trees. It also tolerates semi-arid conditions, but prolonged dry periods reduce vigor and fruiting. It prefers 1,200 to 1,600 mm of annual rainfall and tolerates approximately 700 to 4,000 mm. The tree is moderately wind-resistant and tolerates seaside conditions, but it is not highly salt-tolerant and should be protected from direct salt spray. Young trees benefit from partial shade and do not transplant well, so pot them up early and plant them out while still small.^[2] Its native soil setting is best understood as moist, seasonally wet ground along canals, streams, and other low-lying drainage lines rather than permanently stagnant swamp. Deep loam is ideal, but the species also grows on sand and limestone with little organic matter. That combination suggests a tree that appreciates a steady water supply while still benefiting from aerated root zones. Heavy clay can work if excess water can drain away after rain; permanently waterlogged, anaerobic soil is a poorer choice even though the tree tolerates wet feet better than many fruit trees. In a garden, improve compacted clay with organic matter and use a raised planting position where water stands for more than a short period.^[1][2]

Soil

In its native tropical setting, rose apple is often found on deep, moisture-retentive soils beside streams, canals, and other drainage lines. These soils may be alluvial loams with a substantial leaf-litter layer. The species also tolerates sand and limestone soils, but natural wetness should not be confused with permanently stagnant swamp; roots still need oxygen and drainage between floods.^[2]

Sun and humidity

Mature trees fruit best in full sun, while young trees benefit from partial shade during establishment. The native climate is humid and warm, with regular atmospheric moisture. Shelter from drying winds is useful even though established trees tolerate wind better than many tropical fruit trees.

Seasonal changes

Growth is strongest during warm, wet periods. In climates with a distinct dry season, flowering commonly occurs toward the end of the dry period and fruit develops as rains return. Cooler subtropical winters slow growth, and repeated frost can stop fruiting even where the tree survives.^[2]

Propagation

• Seed is the standard method. Seeds are recalcitrant, with no dormancy and a storage life measured in days, so sow them fresh after cleaning. Germination takes 10 to 120 days. Seeds are polyembryonic, meaning that one seed can produce 3 to 8 seedlings, most of them close to the parent type. Surface-sow in shade, firm the seed into the medium, and keep it moist. Young plants transplant poorly, so pot them individually before the roots become crowded.^[1][2]
• Air-layering is the most useful clonal method. Spring layers treated with 1000 ppm NAA have produced about 60% rooting. Air-layers taken during the rainy season may fail to root. In West Bengal, air-layering is performed in July, with planting out in October and November.^[1]
• Cuttings and grafting have produced inconsistent results. Hardwood cuttings did not root even with hormones, while semihardwood cuttings achieved about 20% success. Chip and T-budding were unsuccessful. Veneer grafting of spring-flush scions onto one-year-old rootstocks succeeded in about 31% of plants.^[1]

In India, vegetative propagation work has focused on selecting and maintaining dwarf types. These selections may be particularly useful for container growers.

Flowering, fruiting and harvest

Cream-colored flowers in terminal clusters. Photo by Ajtjohnsingh, CC BY-SA 4.0, via Wikimedia Commons.

The species is self-fertile, and bees and other insects provide pollination. Flowers are produced on new growth, from late winter through spring and early summer in the subtropics, and sporadically throughout the year in the deep tropics. A tree may carry ripening fruit while producing additional flowers.^[1]

In the native Southeast Asian range the calendar follows the rains. Bloom comes in the dry season, and fruit follows 8 to 12 weeks later, early in the wet season. Regional examples:

• South India: blooms January, ripe March to April
• Central India: blooms February to April, ripe June to July
• Jamaica and Puerto Rico: sporadic nearly year-round, a bit less in summer
• Florida and Bahamas: main crop May to July^[1]

Fruit is non-climacteric and should be harvested at full color. It bruises easily and deteriorates quickly after picking, which limits its value for commercial shipping. Crops are modest. A mature tree in India yields approximately 2 kg per season.^[1]

Fruit and uses

Fruit cut open, showing the loose seeds in the hollow center. Photo by JonRichfield, CC BY-SA 3.0, via Wikimedia Commons.

The fruit is best eaten fresh, when the skin and crisp flesh are still firm. The hollow center makes it light and refreshing, with a rosewater scent. Some descriptions compare the flavor to apple and watermelon with a mild rose aftertaste. Other uses include:

• Jam or jelly, usually with lemon juice to sharpen the delicate flavor
• Syrup for cold drinks
• Stewed with sugar as dessert
• Candied halved fruit the Jamaican way (stewed in heavy sugar syrup with cinnamon)
• Stuffed and baked (halved, filled with sweet or savory filling, baked about 20 minutes)

The flowers are edible and provide useful bee forage. The tree is a minor honey source in Cuba. The seeds should not be eaten; they are reported to be poisonous. Hydrocyanic acid has also been reported in the roots, stems, and leaves.^[1][5]

Pests and diseases

The species has few serious insect problems. In humid climates, the main reported problems are:^[1]

• Aphids, with sooty mold following on the honeydew
• Leaf spots: Cercospora, Gloeosporium, Phyllosticta; algal leaf spot (Cephaleuros); anthracnose
• Root rots (Fusarium, mushroom root rot) on badly drained sites

Container-grown plants may experience fewer leaf-spot and sooty-mold problems than trees grown in humid tropical conditions, especially when good air circulation is maintained.

Cultivars and selections

Few formally named cultivars are documented.^[1] Most trees are seedling-grown, and polyembryony means that many seedlings remain reasonably close to the parent type. The most obvious variation is in fruit color, from pale yellow to pink-blushed, and in fruiting time. Some Indian selections fruit in February and March rather than during the usual June and July crop. India has also investigated vegetative propagation to maintain dwarf types.

Growers who find a tree with superior flavor, larger fruit, or an earlier season can preserve those traits by air-layering. Seedlings may not reproduce the parent tree exactly.

Container growing

Rose apple is well suited to container culture.^[4] It has a naturally branched habit, can fruit in a pot, and can be maintained at 2 to 3 m with regular pruning. This makes it a practical choice for growers in marginal climates who need to move the plant under cover during winter.

• Pot size: Start in a 5-gallon container and move to a 15- to 25-gallon container as the tree matures. Use a well-drained potting mix amended with perlite or pumice.
• Water: Keep the mix evenly moist, but do not allow the container to remain waterlogged. Container-grown trees dry out faster than trees in the ground.
• Fertilizer: Apply a complete fertilizer containing micronutrients two or three times per year. On high-pH soils or with alkaline irrigation water, watch for micronutrient deficiencies and use foliar correction when appropriate.
• Light: Full sun once established. Young plants benefit from some shade. In marginal zones, place the container where it receives maximum sun and reflected heat.
• Overwintering: Growers in zones 8 and 9 can keep a container tree in a greenhouse or move it indoors during freezes. It needs warmth to fruit, so a cool, dark winter may preserve the plant without maintaining productivity.
• Pruning: The tree tolerates hard pruning and has been used as a living fence in Guatemala. Prune to control height and width, and remove weak or crowded branches.

Zone pushing

For growers in zones 8 and 9 testing the limits of outdoor culture:

• Mature trees survive brief dips to -3 °C (26 °F), but young trees require protection.^[2][6] Cover the canopy and mulch the root zone when frost threatens.
• Regular freezes usually prevent fruiting. In areas that freeze every winter, the tree is more likely to remain ornamental than productive.
• A south-facing wall, protection from frost pockets, and overhead canopy cover can improve an in-ground tree's chances by moderating cold.
• Container culture with winter protection is the most reliable strategy in marginal zones. The tree can be moved indoors or into a greenhouse during cold weather.
• In coastal California, the tree may grow vigorously without setting fruit. Adequate heat accumulation is important for flowering and fruit set.

References

1. ↑ Morton, J. 1987. Rose Apple, Fruits of Warm Climates. Purdue NewCROP. Includes descriptions of the fruit, seasons, propagation, yield, pests, uses, and reported hazards.
2. ↑ Useful Tropical Plants: Syzygium jambos. Climate tolerances, polyembryony, germination, transplanting, and frost tolerance.
3. ↑ Growables: Syzygium jambos. USDA zones, common names, and related species.
4. ↑ Top Tropicals: Rose Apple. Container culture, fruiting, care, and cold tolerance.
5. ↑ Plants For A Future: Syzygium jambos. Hardiness and reported hazards.
6. ↑ San Marcos Growers: Syzygium jambos. Frost tolerance and the relationship between cold conditions and fruiting.

Image credits

• Whole fruit: PMATAS, CC BY-SA 4.0
• Flowers: Ajtjohnsingh, CC BY-SA 4.0
• Young leaves: Tonton Bernardo, CC BY-SA 3.0
• Fruit and seeds: JonRichfield, CC BY-SA 3.0
• Tree habit: Forest & Kim Starr, CC BY 3.0