Pity poor Hylocereus undatus.1 Though a perfectly interesting species in its own right, you'll never see it when you're looking over the plants at your local Lowe's or supermarket or garden center or wherever you buy them, even if you're looking directly at it. Why's that? Because 99.99% of the time, you're seeing this:
These brightly-colored cacti are actually two different species of cacti grafted together. The top plant in these photos is a Gymnocalycium species, often called "moon cactus," which has mutated in such a way that it is unable (or maybe just unwilling: they seem kind of spoiled if you ask me) to produce the chlorophyll it needs to photosynthesize. These have been around for years: I remember seeing them as a little kid. The ones I remember, though, were always kind of a neon red: the pinks and yellows and oranges and purples like in the picture are a semi-new development.
The Gymnocalycium produces offsets pretty easily, even when grafted, and the offsets so produced can be grafted to a new base, perpetuating the plant, though it's my understanding that even the best grafts only last a few years, as the base grows faster than the Gymnocalycium. After that point, the difference in speed between the two becomes too great for the graft to hold together, and the two split apart. Some of the sites I ran across in researching this one seemed to be suggesting that the Gymnocalycium, if removed from the base and replanted, will remain colored until it dies from lack of food; other sites implied that severed grafts would spontaneously begin to produce chlorophyll even though they never had previously, and could be planted on their own. My personal suspicion is that both are true: the "purple" grafts, if you look closely, do contain some green, towards the center of the plant:
So they probably could begin making food for themselves if they really needed to. Peanut butter sandwiches, at least. At the same time, the neon yellow and orange and pink give no indication of having any green pigment in them whatsoever, and so I would guess that those probably couldn't make it on their own. We do have a few plain green Gymnocalycium at work, but they don't do anything terribly interesting and just look like your ordinary small green beanbag-shaped cactus. A couple of them do color up a little in the summer: they stay green but have a red / purple cast to them, especially on the most exposed portions of the plants. It's not especially attractive: mostly they just look kind of burnt.
But who cares about the Gymnocalyciums anyway, right? What we're really interested in is the base, the sad little, put-upon, servant of a plant that's doing all the heavy lifting.
The above is my own personal plant. I got it from Lowe's, after an excruciating wait to see whether anybody else was going to take it. It was one of a number of grafted cacti they had, all of them Gymnocalycium/Hylocereus types, but on this particular one, the graft had come off, and there were sprouts from each corner of the Hylocereus. I wanted to buy it, but the original plant was like $3.47, which seemed like a lot for a plant that was kinda, you know, broken. So I waited, and waited, and then finally there it was, waiting for me, on the half-price racks.
It's done well for me so far. It grew really quickly when it first arrived, and has settled down a little bit now that we're in the middle of winter. One of the bigger surprises was the sudden appearance of aerial roots from the center of the stem segments:
This is perfectly normal, just not something I was expecting to see. The aerial roots are like aerial roots on anything else: they're not mandatory. If you don't like them, you can cut them off; if they dry up and die, the plant isn't necessarily hurt any.
The thing I was most surprised about, though, was that when I started looking into it, I found out that this was the same plant that gives us the dragon fruit, or pitaya. As a bonus surprise, I found out that "dragon fruit" really existed: I'd actually assumed that there was probably no such thing. (Based on the name, it sounded like a marketing ploy to me, and it's not like I'd seen any in the grocery store.)2 But they are real, and they look like this:
I think you'll agree that "dragon fruit" seems like an appropriate name. The interior of the fruit is full of small, crunchy black seeds, which are (I hear) pretty easily sprouted; the pulp surrounding the seeds is white, pink, or red, depending on its ancestry. It is apparently typical for the fruit to be served chilled, and the flesh scooped out of the rind with a spoon. The taste is said to be something like a melon or kiwi (the crunchy seeds contribute to the kiwi comparison): sweet, but not intense.
The flowers are also kind of a big deal:
The flowers are short-lived, opening only for one night. They're pretty damned elaborate, as you can see from the picture, and are heavily scented. By all accounts, they're awesome flowers, but alas, I've never seen one of those in person either.
Plants have to be large, if not old, in order to set blooms and fruit. Mine clearly has a ways to go. They are supposed to grow faster and do better in general if you give them something to hang onto, like with Monstera deliciosa, though since they get big (20 feet is not unheard of), you're going to want to choose something you can add to over time. They will climb trees in the wild, though they're not picky, and will attach to burlap-covered poles, concrete walls, slow-moving pets, or whatever.3 At least a couple places I ran across on-line seemed to be suggesting that it's reasonable to expect blooms at about two years old and / or two feet tall; to get fruit you need somewhat bigger plants, and the flowers have to be pollinated. I haven't seen anybody address the question of whether plants are self-fertile.
Care is fairly typical cactus, though since this is a jungle species (the Hylocereus genus as a whole is native to the Caribbean and Central America south to the northmost part of South America), it's somewhat more flexible about certain things. Full sun is desirable indoors; the plant can be moved outside during the summer but should be shaded from the hottest summer sun, and obviously one will want to make any big shifts in light level somewhat gradually. The plant adapts to a pretty wide range of soils, and tolerates very hot and very cold conditions (up to 110ºF/43ºC, down to freezing or below, though they can only withstand short periods of cold, so don't push this too hard). Humidity is essentially a non-issue.
Propagation is said to be pretty simple: they root easily from cuttings that have been allowed to dry for a day or two: stand the cutting up on a well-draining soil and water when the soil gets dry, and the plant will handle the rest. It's also supposed to be a piece of cake to sprout seeds, if you're lucky enough to get a fruit to take seeds from: my understanding is that a moist but not soggy, fairly loose soil mix, seeds sprinkled around on top, and a plastic bag over the top of the mix is all you really need. Seedlings can be transplanted when they've grown beyond their seed leaves.
I'm a little clueless on watering; I've been going with the standard cactus approach of letting it get pretty dry between waterings, which with my plant winds up being about every 10-14 days. So far, so good, though I have seen a few things around the net that suggest that this needs to be cut back even further during the winter. So far, there are no complaints, so I'm inclined to keep doing what I've been doing. But we'll see how it goes.
I'm going to assume mealybugs can be a problem, because when the hell are they ever not, but I haven't had any yet.
They're known for getting kind of top-heavy. Wider, shallower pots are sometimes advised for this, to lower the center of gravity, but you still have to bear in mind that the roots only need as much soil as they need, and you can't move them into a pot that's larger than they need without there being some consequences.
I don't expect to get fruit from this plant. I don't even really expect flowers, to tell the truth. But I do like it, all the same, for being this totally cool plant that was hidden in plain sight: crazy flowers, alien-looking fruit, a tree-climbing cactus, and the only time I ever saw it, it was relegated to being the low-key servant for some lazy-ass Gymnocalycium that won't even make their own chlorophyll. Not that you should go to your local plant supplier and start liberating the Hylocereus by knocking off their grafts: that would be wrong, if amusing ("Grow, my pretties! Grow and be free!"). But, you know, sooner or later you'll see one where the graft has come off on its own, through normal handling or whatever,4 and depending on where you find yourself, you may be able to get it for a song, if you ask the right people. And it'd be worth getting.
Photo credits: fruit and flower as noted in text; all others are my own.
2 (I can sometimes be too skeptical for my own good.)
3 There is considerable on-line disagreement about exactly how fast these grow, with some sides saying they're practically a blur and others saying that they take forever to get anywhere. Based on the speed of my own, thus far, and the information at this site, I lean towards blur, but your results may vary, especially if you and I actually own different species. Selenicereus spp. are similar-looking, and also have big Las-Vegas-showgirl flower production extravaganzas, but appear to work much more slowly. Also different Hylocereus species can, I think, reasonably be expected to grow at differing speeds. Anyone with actual information about this, even anecdotal, is encouraged to share in the comments.
4 Thus far, nothing like this has happened to the batch we got a couple weeks ago, for which I am grateful. They've actually even sold pretty well. I'm not a fan of grafted cacti, never have been, and I liked them even less well when I read that the graft isn't stable for more than a few years, so I was kind of against ordering them in the first place, but apparently the rest of the world likes the damn garish and fake things better than I do.