Papaya is a short-lived perennial growing to 30 ft (9.14 m) high. Its hollow, herbaceous stem is usually unbranched. The deeply lobed, palmate leaves are borne on long, hollow petioles emerging from the stem apex. Flowers occur in leaf axils. Older leaves die and fall as the tree grows.
Papaya flowers are fragrant and have five cream-white to yellow-orange petals 1 to 2 in (2.5 to 5.1 cm) long. The stigmatic surfaces are pale green, and the stamens are bright yellow.
Papaya fruits are smooth skinned. They vary widely in size and shape, depending on variety and type of plant. Hermaphrodite plants of commercial ‘Solo’ varieties in Hawaii usually produce fruits that are pear shaped and weigh approximately 12 to 30 oz (340 to 851 g). Female plants of ‘Solo’ varieties produce round fruits. Other papaya varieties produce variously shaped fruits, which may weigh up to 20 lb (9.1 kg). The fruits usually contain many seeds surrounded by a smooth yellow to orange-red flesh that is sweet in good varieties.
Flower type. Flower type is determined by the presence or absence of functional stamens (male parts) and stigma and ovary (female parts). Within varieties, flower type is usually identified by flower size and shape.
Female flowers are relatively large and rounded at the base. They have a stigma but lack stamens. They generally must receive pollen in order to set fruit. Pollen can be carried by wind or by insects.
Male flowers are thin and tubular. They have perfect structure (i.e., they contain both male and female organs), but the small, vestigial ovary is nonfunctional. Male flowers are usually borne on a long flower stalk (peduncle).
Hermaphrodite flowers are intermediate between female and male flowers in size and shape. They are less bulbous than female flowers, but not as thin as male flowers. They have perfect structure with functional stigma and stamens and usually are self-pollinating.
Plant type. Three types of plants are recognized based on flower type: female, hermaphrodite, and male.
Female plants always produce female flowers. If no male or hermaphrodite plants are nearby to provide pollen, female plants usually fail to set fruit. Unpollinated female plants occasionally set parthenocarpic fruits, lacking seeds.
Male plants are distinguished by their long flower stalks bearing many flowers. Usually they do not produce fruit, but on rare occasions there is female expression in the flowers, and they may set fruits .
Hermaphrodite plants may have male flowers, hermaphrodite flowers, or both, depending on environmental conditions and the time of year. Hot, dry weather may cause suppression of the ovary and the production of female-sterile (i.e., male) flowers. This accounts for occasional seasonal failure of hermaphrodite plants to set fruit. Male flowers on hermaphrodite plants are borne on short peduncles.
Hermaphrodite plants tend to produce selfpollinated seeds, which result in relatively uniform progenies. Seeds from hermaphrodite plants of ‘Solo’ varieties characteristically produce one-third female and two-thirds hermaphrodite plants, but no male plants are produced.
Although hermaphrodite and female plants have similar fruit texture and quality, female plants may be less productive, and the round female fruits are marketed only in small quantities in Hawaii as direct sales from growers to consumers. Female plants are removed from commercial orchards as soon as they can be distinguished at flowering. In home gardens, female plants may be kept if hermaphrodite or male plants are nearby to serve as a pollen source.
Papaya grows well on many types of soil, but they must be adequately drained. Restricted soil drainage promotes root diseases. Most commercial production in Hawaii is on porous aa lava. Production on other soil types is limited to low rainfall areas where restricted drainage is less likely to cause problems. Heavy clay and pahoehoe lava soils should be avoided. Soil pH near neutral (pH 6.0 to 7.0) is preferred.
Soil categories used for commercial production vary from island to island. On Hawaii, both aa lava and soils are used. On aa lava lands, additional soil is usually brought in and placed in the planting hole. The soils used for papaya on the island of Hawaii have a high preplant phosphorus fertilizer requirement. These soils, as well as the organic soils derived from lava, are usually acidic, and liming may be necessary. On Kauai the soils used for papaya usually require liming and high levels of phosphorus fertilization. On Oahu the soils on which papaya is grown are often poorly drained.
Papaya grows best in warm areas below 500 ft (152 m) elevation. Fruit production and quality decline at higher elevations, where cooler temperatures cause flower drop and cat-faced (carpelloidic) fruits. (Carpelloidy is the abnormal development of stamens into fleshy structures.)
Papaya can tolerate moderate winds if well rooted. Forty to 60 in (102 to 152 cm) of rainfall evenly distributed throughout the year is adequate for growth. With higher rainfall, soils should be porous and well drained. Planting on slopes or on raised hills helps to prevent waterlogging.