By Richard Frost, for Let’s Talk Plants! October 2021.
The Guatemalan dragon fruit, S. guatemalensis, harvest from a plant in the SE corner of the author's Vista, CA yard. None were hand pollinated. Posted July 23, 2021 Richard Frost Facebook.
About two decades ago I learned about Dragon Fruit from a colleague in the California Rare Fruit Growers. I looked it up in my then new copy of Cornucopia II. I heard that the red fruited varieties were the best tasting so I ordered Pitahaya Roja, Selenicereus ocamponis, from reference G18. The following year I shared a cutting of it with Edgar Valdivia who rebranded it Valdivia Roja. That year I also received Guatemalan Pitahaya, S. guatemalensis, and Physical Graffiti, S. hybrid? from Ramiro Lobo, and the following year Paul Thomson gave me a cutting of his S. undatus selection. Those plants and others grew slowly at first, but picked up speed later - eventually I was pruning them twice a year. Since those early days thousands of named cultivars have emerged among collectors and sellers.
All dragon fruit species and most of the cultivars and hybrids are self-fertile and intra-fertile. The issue is with getting pollen from the anthers to the stigma - which typically is extended well past the anthers, and also with knowing when the pollen is ripe. In nature there are tiny beetles - about half the length and width of an ant which visit the plant in the early morning when the flower is closing. They are attracted to the interior of the flower and wander around in there, inadvertently pollinating the ovum. In fact, I have seen them, here in Vista and previously in Peñasquitos. But local beetles typically aren't aware of newly established plants and so it's a good idea to hand pollinate for the first several years. A toothbrush or a short horsehair 1/4" wide paintbrush works well.
Flowers typically sprout on pods that grow out in the early spring or have overwintered at least once. The quantity of flowers depends upon the quantity of soil roots and air roots, plus local climate and cultural practices. I water them once per week and feed them 20-10-20 orchid food the equivalent of once per month - in moderation. There is no need to stimulate them with bloom formula, which sometimes can have deleterious effects. They are susceptible to bacterial spot disease which is unavoidable as it is hosted by western chaparral plants. However, you can keep it to a minimum by treating them in winter, spring, and fall with a copper spray such as LiquiCop.
Dragon fruit plants can become unwieldy with age. I recommend providing them a large trellis and tying them with clothesline rope to secure the pods for several years of production. Also don't be afraid to use clippers to keep them to a manageable size.
Selenicereus ocamponis has thick, heavy pods and the flower sepals are variegated red and yellow. It is a shy bearer at first but once established the pods are eight feet long and produce a lot of fruit the following years. It is my favorite for taste.
The Guatemalan Pitahaya was rebranded "American Beauty" by Pine Tree Nursery in Florida twenty years ago. It has "standard" pods but produces excellent, red-fleshed fruit. This one and the Roja are the only ones I grow nowadays.
Physical Graffiti has slightly more bulky pods than the Guatemalan but the same skin color. The fruit flesh is light red. I'm guessing it is a selection of undatus x polyrhizus. In my opinion it has an okay but slightly bland flavor.
The S. undatus have "standard" pods with white-fleshed fruit. In my opinion they are like a sweet but flavorless melon. However, they are preferred in the orient where the red fleshed is less popular. Thomson's is very good for an undatus.