Hydroponic How-to: Dragon Fruit
Colorful, healthy, delicious, and well-suited to thrive in a hydroponic setup, dragon fruit are quickly becoming popular among indoor growers.
Vividly colored and clad in scales, dragon fruit, also known as pitaya, is an exotic fruit growing in popularity for its purported health benefits. While native to the tropical rainforests of Central and South America, dragon fruit have been cultivated in Asia for more than 100 years and are now being identified as a potentially profitable commercial greenhouse crop. With skin colors ranging from deep red, pink, or yellow, the flesh is succulent, sweet, and flecked with small black edible seeds. Plants are prolific and fruit size is typically between 350-450 grams, however, some cultivars can produce fruit of up to 900 grams. Usually eaten as a fresh fruit with flesh which ranges from white to deep red, pitaya can also be used in juices and smoothies as well as jellies, ices, yogurt, and similar dishes.
Dragon fruit (Hylocereus sp.) are a unique crop because the fruit are produced on a large, climbing cactus which, in their native environment, trail up tree trunks and are anchored by aerial roots. Under cultivation, the plants are provided with supports or stakes and pruned to restrict height and improve productivity. Plants are long lived and can be kept in production for up to 20 years with the first fruit forming within two years of propagation from cuttings. The dragon fruit plant has fleshy triangular stem segments that are tied to trellising systems to support the weight of the fruit and provide a surface to which the aerial roots can anchor.
Plants require a warm, humid climate, however, unlike many desert cacti, dragon fruit are sensitive to high light levels and require shading for optimum growth and yields. Having adapted to the growing conditions of a tropical rainforest understory, plants need protection from intense sunlight as excessive light will cause the stems to become bleached and restrict growth. Under hydroponic production the use of shade or net houses provides an ideal climate, however, dragon fruit can also be grown indoors under artificial light sources when plant size and height are carefully controlled. Being tropical or subtropical in nature, dragon fruit plants require warm temperatures in the optimal range of 77-90°F, though temperature sensitivity varies between different cultivars. Most pitaya plants can withstand cool temperatures for a short period of time, although this will delay growth and development. Temperature extremes of below 37°F and above 112°F will damage plant tissue and may result in plant death.
Propagation and Young Plant Care
What makes dragon fruit a particularly appealing new crop for small hydroponic growers is it can be easily and rapidly grown from seed collected from mature fruit.
With dragon fruit becoming more available, extraction of the small, highly viable black seeds from the flesh and germinating these to grow a few plants is relatively simple. Seed should be well washed so all flesh is removed and can be sown immediately onto a sterilized, fine seed-raising medium and lightly covered. Under warm temperatures of 77-81°F these should germinate within three weeks and can be grown until large enough to plant into a hydroponic production system. Young dragon fruit plants make attractive specimens as house plants and have the appearance of a tall cactus with a similar growth habit. The main issue with seed-raised pitaya plants is the time to first fruit production is slower than plants propagated from cuttings, taking up to four years. Seedling growth is relatively slow in the first one to two years.
Read also: Growing Fruit Trees Using Hydroponics
Propagation from cuttings is the preferred method for commercial plantations of dragon fruit and ensures newly raised plants are genetically identical to the parent so will have known fruiting characteristics. If cutting material can be obtained from a suitable cultivar, it’s a more rapid method of establishing a crop. Dragon fruit plants produce a large number of side shoots that can be removed and used for propagation. Well-hardened cutting material of at least eight inches or longer is sliced from the parent plant and the cut surface allowed to cure and callus for a week before planting out. This process helps to prevent rotting during the root formation stage. Cuttings are then placed into a free-draining, sterile rooting medium and left under warm, shaded conditions or on a heated propagation bed until new roots have formed.
Dragon fruit plants can be grown in a containerized system and respond well to the controlled irrigation of hydroponic systems. Since at fruiting the long-lived plants are large and require support, a suitable root volume needs to be provided. Dutch bucket systems or containers with at least 12 inches of depth are suitable for young plants. At the time of planting out, a stake or support needs to be installed for the young plant to climb. The main stem should be pinched out at the top once it reaches the height of the support post. After this, three to four branches will grow and extend outwards. These will bear the first fruit of the plant. Branches need to be guided to grow downwards and have the tips pruned out when they reach around three feet in length. This helps restrict the height of the plants by preventing unpruned stems growing upwards indefinitely and maintains a more productive and compact plant shape.
Drainage is essential with dragon fruit plants, with substrates such as expanded clay, gravel, and coarse perlite being mediums that help prevent over saturation of the root zone. Drip irrigation of nutrient solution in either an open or closed system is suitable and helps to maintain aeration around the roots. While dragon fruit require a similar amount of water under warm growing conditions as mature tomato or cucumber plants, this needs to be applied in small but frequent amounts as the root system is quite shallow and fibrous.
Water and Nutrient Requirements
Like most fruiting crops, dragon fruit requires higher ratios of nitrogen in the vegetative stages of growth and increased potassium when in fruit. Since a number of relatively large fruit are produced in a short time frame on each plant under optimal growing conditions, sufficient potassium needs to be supplied to maintain fruit yields and quality. Pitaya do not require the same high Electrical Conductivity (EC) that may be applied to crops such as tomatoes to maintain fruit quality. EC levels in the range of 1.0 for young plants up to 1.4 (with a pH of 5.8–6.0) are suitable for long-term production.
EC levels should be measured in the drainage or leachate solution draining from each growing container to ensure EC is not climbing during warm growing condition as plants are sensitive to salinity damage. Under optimal temperatures, mature plants can use as much as one to 1.3 gallons of water per day or as little as 0.6 gallons under cool growing conditions.
Flowering, Pollination, and Fruit Set
Under indoor or greenhouse cultivation, dragon fruit can be manipulated to increase the length of the flowering and fruiting period. Being a long-day plant, control over flowering with use of artificial lighting is possible and can increase yields and productivity significantly. While day length can be extended with the use of lighting, it is also possible to induce flowering by using a night break by providing a low level of light between 11 p.m. and 2 a.m., similar to commercial cultivation in Taiwan.
Pitaya are night bloomers and fragrant flowers are only viable for one to two nights with petals opening in the evening and wilting by daybreak. In their native environment, moths and bats pollinate the flowers, however, many commercially available cultivars are now self compatible and do not require cross pollination.
Hand pollination, however, can help give higher levels of fruit set and greater fruit weight. This process involves physically removing the anthers from one flower and touching them to the stigma of another flower at the time of opening. Alternatively, the pollen can be collected using a small brush and used to pollinate several different flowers. Once pollination has been successfully completed, fruit development is rapid and harvest typically occurs 28 to 30 days after the flower closes. Once fruit have fully expanded and have a good level of skin coloration, harvesting can occur. However, leaving the fruit on the plant for an additional 10 to 15 days has been shown to improve brix (sugar levels) in many cultivars. Brix levels for dragon fruit are usually between 12 to 13 percent but can be as high as 20 percent in the red-fleshed varieties. Once harvested, fruit can be stored for up four weeks at temperatures of 43-50°F with a relative humidity of 90 to 95 percent to prevent desiccation.
Dragon fruit are a fascinating and attractive plant with fragrant night blooming flowers and exotic fruit. They are also a crop with good potential for the well-controlled irrigation and nutrition that hydroponic methods can provide. Through use of artificial lighting, day-length extension, and careful selection of growing substrates, pitaya are likely to become a popular greenhouse and indoor garden specimen.