Pitaya, also called Pitahaya, Dragon Fruit

Selenicereus (Hylocereus) spp

Information given here focusses on the three main climbing cacti grown for fruit that are most readily sourced in WA: Selenicereus undatus (white-flesh, red skin species, WR), S. monacanthus, formerly H. polyrhizus (red-flesh, red skin, RR) and S. megalanthus (white-fleshed, yellow-skinned, WY).

Origin:

Native to Meso-America, including the Caribbean Islands. Now grown in many areas of Asia and elsewhere. WR and RR are diploid but WY is a tetraploid cross of 2 other species.  Inter-species and even inter-genera crosses are widespread, resulting in plants that are very heterozygous.

Climate:

Sub-tropical to tropical rainforests up to 1800m elevation and rainfall of 350-2000m pa.  Optimal temperature range is 21-29°C; temperatures above 40-45°C and frosts are damaging.  Excessive rain leads to flower drop and fruit rot. Although they are very drought tolerant, best yields are obtained with regular moisture as photosynthesis may decrease by 90% after only a week of water stress.

Plant Description:

This understory genus with a shallow but efficient root system has a vine-like climbing habit supported by surrounding trees or by trellises/posts.  The succulent green and photosynthetic stems, 2.5-5cm wide, have 3 flanges or ribs, spines instead of leaves and aerial roots. The spines occur in clusters of 1-5 (areoles) spaced 4-6cm apart along the stem edges.  Selenicereus use CAM metabolism for photosynthesis, making them extremely efficient in water use and able to survive under dry and arid conditions.

Relatives:

Cactaceae Family.  There are many other fruit-producing cacti: columnar, tree-like, creeping, shrubby or small globular, but the principal ones are Opuntia (cactus or prickly pear) and Cereus. Considerable polymorphisms are seen in Selenicereus, with variations in flowers, stem and fruit contributing to difficulties in taxonomy.  The Family consists of 120-125 genera and approx. 1600 species.

Soils:

Fertile soils are best but will still grow although with lower yields in very unfertile soils.  Most cacti do not tolerate soil salinity well.  There is a positive response in growth to the amount of organic matter in the soil.

Propagation:

Seeds or vegetatively. Almost any part of a cactus will regenerate a plant. Seeds are essentially only used for breeding experiments.

Cultivars:

There are many different varieties with different characteristics. Some have local names.

Flowering and Pollination:

The large and beautiful fragrant white flowers, up to 30cm long and wide, open for one night only usually from spring to late autumn. They open just before sunset and close just after sunrise. There are numerous stamens on a slender anther stalk and an unusually large style up to 20cm long.  The stigmas have 24 slender creamy green lobes.  WY is generally more self-fertile than the other two.  Pollination is primarily by moths, bats, bees and maybe ants. If all else fails, try hand pollination.

Cultivation:

These species grow well in shaded conditions necessary to avoid stress responses with extreme sunlight and heat.  They will become large, heavy vines that require a substantial support like a tree, a wall, a post or a purpose-built trellis. Avoid working the soil near the plants, to protect the shallow roots.  Flower induction is enhanced with reduced watering during winter-spring but thereafter good moisture levels should be maintained. Even under similar conditions and management, there is large variation in propensity of flowering and fruiting between varieties.  They respond to regular fertilizer, particularly N and K, either by foliar or soil administration.  Micronutrients may need attention, especially in alkaline soils.

Wind Tolerance

Given good support, they fare well. Pieces may break off.

Pruning:

Carry out regular inspections and remove excess and old growth.  Post-harvest pruning encourages the growth of new young shoots that wil bear flowers the following year.

The Fruit:

Fruits are ovoid, WR and RR 10-15cm long X 10cm wide with WY less than half this size. WR and RR have attractive green, yellow or pinkish pointed scales, 2.5mm long, around the periphery with hundreds of small edible black seeds in the pulp. WR and RR fruits can weigh up to 800g, WY up to 350g. The latter have a higher sugar level and are usually sweeter than the other two. There are spines on WY fruit but these either abscise or can be rubbed off when mature. Fruit size is related to the effectiveness of pollination and seed number, and flesh weight is about 70% of the whole fruit. There is a reasonable level of vitamin C and antioxidants.

Fruit Production and Harvesting:

Cropping with cutting-grown plants may begin within 2 years and yield will steadily increase over the next several years.  WR and RR fruits begin to ripen 4-5 weeks after flowering; WY may take 12-20 weeks.  WY yield is less than for the other two. Cropping is staggered over some months, suiting the home grower.  For full flavour as a non-climacteric fruit they are best picked when fully coloured; this is compromised if insufficiently mature.

Fruit Uses:

They have a delicate texture, and good varieties are delicious eaten fresh or after chilling by simply cutting them in half and spooning out. They’re also dried or frozen (they can be frozen whole) and used in ice creams, fruit salads, purees, jams and marmalades.  The sugar/acid ratio is typically high, so addition of some lemon juice may improve taste for some people.  Storage life at 10°C is about 14 days.

Other parts of the cactus can be eaten, such as the cladodes which have been peeled, sliced in strips and cooked. The flowers can also be cooked.

Pests and Diseases:

In Australia, birds, possums, rats, or bats may be the main cause of any problems.

Comments:

Fruits are most attractive and marketers say this is the main selling feature.  But they’re more than that – very productive in our dry climate provided you give them a shade screen for our very hot summer weather.  Strong support is needed as over the years they become quite heavy.  Try and obtain cuttings from plants you know to be tasty and relatively self-fertile.  With WR and RR plants, different varieties will assist cross-pollination but for top yields you might still need or wish to hand-pollinate. 

Be aware that other species of edible cacti fruit can be called 'pitaya'.