Night blooming cactus
The Florida Extension has an extensive publication with information on this plant:
For home culture, the University of Oklahoma Microbiology Dept offers this information:
Hylocereus undatus or Night-Blooming Cereus, is widespread in the American tropics. Its exact origins are unknown. The stems are 3-winged and green with wings that are 1 to 2 inches wide. Areoles are about 1 ½ inches (4.5 cm) apart with 1 to 5 spines to 5/32 of an inch (1 cm) long. They climb by use of aerial roots and can reach a height 30 feet (~10 meters) or more growing on rocks and trees. As indicated by the name, the blooms appear at night and soon close after the day starts.
Blooming Time: In late spring to early summer the very large white fragrant flowers adorn the plant. Individual flower are 14 inches (35 cm) long by 12 inches (30 cm) across ... very showy! If pollinated, they produce edible red fruits up to 5 inches (12 cm) long.
Culture: Hylocereus undatus need full sun to partial shade with intermediate to warm temperatures. We use a well-drained soil mix consisting of 2 parts sand to 1 part loam to 1 part peat moss. During the growing season (March-August), the plants are watered on a regular basis, making sure that they never dry out completely. They are fertilized on a monthly basis with a balanced fertilizer during this period. In late August, water is restricted to about once a week until January. Night temperatures at this time should be about 50° F (10° C). In January or February, watering is stopped for a period of 4 weeks to aid in flower formation. In March, regular watering is resumed and the plant will flower in 6 to 8 weeks.
Propagation: Hylocereus undatus is propagated by cutting or by seed in the spring. Seed should be sown in well-drained compost and should germinate in 14 to 28 days at 65° to 70° F (18° - 21° C).