By Larry Hodgson
Question: When I received this cactus, it had only a central stem with another colorful cactus on top. However, attractive top part died and for several years now, it has been growing very strangely. What should I do with this weird cactus?
Answer: Cacti with a colored cactus grafted on top of the stem of a green cactus are very popular. The red ball cactus (Gymnocalycium mihanovichii friedrichii ‘Rubra’, also called Hibotan), a small globular cactus that is entirely red, is the most common of these grafted cacti, but there are other colors and forms. Most are albinos and can’t survive unless they are grafted onto a photosynthesizing (green) cactus stem.
Usually, these cacti don’t live that long: a year or so, sometimes a bit more. Either the rootstock (the green part) dies, taking the root system with it, and then the whole plant is (obviously) dead or the scion—the colored part—dies, leaving you with only the rootstock, the green cactus, which is much less attractive. That’s what happened in your case.
Is the Rootstock Interesting Enough?
So, your pot now contains only the rootstock, the green stem the colorful cactus was grafted onto. What is it?
The traditional rootstock for commercially produced grafted cacti is the Queen of the Night cactus (Selenicereus undatus, syn. Hylocereus undatus or S. triangularis, syn. H. trigonus) and that is indeed what you have. At first, all you see is a green stem with the top cut off, but, as you’ve noticed, over time branches start to form. In nature, this cactus becomes a huge climbing plant. Its stems don’t wrap about stems and trunks like twining plants do, but instead produce aerial roots that cling to rough surfaces and even many smooth ones and thus help it grow up trees in the wild. That’s what the aerial roots clearly visible on your plant are doing: looking for something to cling to.
I must admit your cactus doesn’t look very healthy. I suspect it isn’t getting enough light. Even though the Queen of the Night cactus generally grows in an environment partially shaded by large trees in the wild, in our homes, where it’s always much more somber than we like to think, it really should be in full sun or nearly full sun, with several hours of intense light each day. For that reason, a location near a large south-facing window would help it grow more vigorously.
Also, you should repot your plant into a larger pot; one that has drainage holes, of course. You can use cactus soil or regular potting mix in doing so. It’s better to repot it in the spring or summer, when days are longer, than in fall or winter.
As for caring for this plant correctly, this is not your typical desert cactus, a plant the prefers long periods with no water at all, but rather grows under mesic conditions (in moderately moist soil), so follow the golden rule of watering and water thoroughly when the soil feels dry to the touch. Normal indoor temperatures are fine and a little fertilizer every now and then during the growing season will help your Queen of the Night cactus put on more vigorous growth.
Waking Up the Sleeping Dragon
However, when you give good care to a Queen of the Night, it tends to overstep is bounds. You’ve essentially woken up a sleeping dragon.
Well-cared for, your little awkward-looking cactus will turn quite readily into a big, unruly thug of a plant. It will send long branches out in all directions, branches that can easily reach 7 feet (2 m) in length, even much longer outdoors in the tropics where the plant can grow outdoors all year. And you might not find it all that attractive. Typically, people growing this giant indoors attach it to a large trellis or let it climb the walls, removing or shortening any branches that become excessively long, a type of pruning it tolerates surprisingly well. Many people who grow it in this way end up offering it most of the space in the room: a green wall in a sunroom, for example. Yes, it really turns into a dragon when it begins to expand!
On the other hand, after years of care (usually 10 and more), this big but none-too-pretty climbing cactus plant will show you where it gets the name “Queen of the Night” and start to bloom. The flowers are huge and gorgeous: white, trumpet-shaped and exquisitely scented. And they open only at night, closing early in the morning the next day, then fade, never to open again. The flower can measure 8 to 12 inches (20 to 30 cm) in diameter, depending on the variety. With such blooms illuminating the darkness, the plant truly is a Queen of the Night!
A ten-year wait for less than 10 hours of bloom? That might seem unreasonable, but … at least this first flowering indicates that the plant has reached maturity. So, from this moment on, it will probably bloom every year with more and more flowers every time. Some plants produce dozens, even hundreds of these giant flowers!
What About the Fruit?
Now for a bit of a surprise. The humble rootstock plant that turned into the striking Queen of the Night cactus also produces a fruit: a large, delicious fruit, sold in supermarkets everywhere under the names of dragon fruit or pitaya. Yes, those big red fruits with white flesh dotted with small black seeds come from a climbing cactus!
Outdoors in a tropical climate (hardiness zones 10–11), bats and insects take care of pollination. At least, that is, when there are two or more specimens in the area, as cross-pollination is normally required to fecundate the flower. However, the chances of your Queen of the Night producing fruit indoors are almost nil, because it’s very unlikely you’ll have two of these huge cacti blooming at the same time to ensure the necessary cross-pollination. And even if you did, you would have to stay up half the night to carry the pollen from the anthers (at the center of the flower) to the stigma, which emerges from it, yourself. Most homes simply don’t have the needed flower-pollinating bats and insects!
Only then could you theoretically grow your own dragon fruit … but I don’t know of anyone who has actually succeeded in doing this inside a typical home.
If you like a challenge and have lots of space, sure, do apply the above information to try and tame the dragon this plant will become! But if not, maybe it’s time to end the poor plant’s agony, as it obviously doesn’t have the conditions it needs for a happy life presently. As a gardener, you have to learn to know when the time has come to say goodbye to a plant that is simply not giving you the desired results.