Sunday, November 18, 2007

Dancer (Cereus peruvianus)

To be honest, I find the whole cactus family to be one big confusing blur. I know a lot of the names – Mammilaria, Ferocactus, Opuntia, Rebutia, Cephalocereus, Echinocereus, Parodia, Myrtilocactus and so forth – but telling them apart from one another is often more than I can manage. It doesn't help that the names change sometimes, further mixing up any small bits I've been able to pin down.

So for me, the cactus table at work is sort of like a huge family reunion for someone else's family – it's a big blur of individuals who all kind of look the same, more or less; at the same time, I can also tell that some of them are more closely related to each other than others. There are far too many of them to be able to meet them all, so I just greet everybody with a hearty cry of, "Heyyyy . . . uh, you. Guy," and hope that's good enough.

The exceptions are relatively few and far, but Cereus peruvianus is one. If that is, in fact, its real name (something I'm also confused about), and if I've identified it correctly (if I got it wrong, it's not for lack of trying; I've looked at so many pictures of bluish, columnar cacti with reddish spines that were all identified differently that I eventually despaired of ever getting a species ID and instead just wanted to get the right genus. Which I think I did.).

I bought these two guys in late February of 2004. They were, at that time, 17 inches (43 cm) tall, and that includes the height of the gallon pots they came in. They are now tall enough that they can look me in the eye: I think the last time I measured, they were five feet five inches (1.65 m), and that's been long enough ago that I know they've grown some since.

I liked them so well that I bought more, almost exactly a year ago:

These were at K-Mart, three to a pot, and I bought them and separated them and then spent many months trying to get the mealybugs off of them. 1 I'm not sure whether this has been successful or not; so far, every time I think I've gotten them all, I've wound up finding more soon after. Though it has been a couple months, now.

They've been doing reasonably well so far, even though (as you'll notice) the smaller ones are in plastic pots. Clay would be better, but I'm not going to worry about it until they need to be repotted: they're doing fine where they are, and they've been fine there for over a year, so I'll move them to clay when they tell me they want to be moved.

They will flower, though none of mine ever have. A recent customer of mine told me that she had one at home that was getting close to eight feet tall (!), that produced flowers. She was in the store because she wanted to cut it back and needed advice, though: apparently her plant is not only getting too tall for her, it's leaning badly, and when it produces flowers, the buds form next to the window it's leaning on, causing them to become deformed and never open properly. Which is a little bit tragic, for those of us who haven't been able to see it for ourselves.

The flowers are lovely, what pictures I've seen of them (I was unable to locate a public domain photo of one before this post; however, you can see some excellent pictures of unknown legal status here and here.), and it would, of course, be extraordinarily cool if one or both of mine did sometime, but I don't actually mind if they don't.

As Christmas approaches, they often like to pretend to be the Radio City Music Hall's Rockettes. I have no idea why.

I've been surprised by customers' ideas about watering cacti. People want to know why their cactus died, and when I ask how much water they were giving it, they almost always say almost nothing at all, honest – I watered it maybe twice a year at most, or something similar. People. You do have to water cacti. Kinda regularly, even. They'll die if they get too much, but that doesn't mean you should never give them any, or that you should only water them when it rains in Tucson (unless you've accurately reproduced the Tucson climate in your living room, which I kinda doubt), or that you should only give them a teaspoon at a time.

Also. Something about cacti seems to make people want to be mean to them, generally in a way that involves glue. They glue fake flowers to them, or cartoony googly eyes, or they top off their soil with pebbles and then glue the pebbles together so that you actually can't water or repot them (which is an ongoing frustration for me personally). I understand all these practices in some way or another – gluing the pebbles together makes them easier to ship, gluing flowers and eyes makes them more attractive to impulse buyers – but, again, you're selling the plant, right? So why wouldn't you want the plant to be good quality, likely to survive, and all that? Apparently not.

Snapshot taken during the All-Cactus Revue's Annual Tribute to Busby Berkeley.

Another bizarre thing people do to sell this species of cactus in particular is to claim that it's especially effective at reducing the radiation (or, in some cases, the static electricity) from cathode ray tubes. One site claimed that Cereus peruvianus is a natural negative-ion generator (read through the comments to see the specific claims). Another said that it can absorb radiation in general. A third claimed that just an extract of Cereus peruvianus would give a person "great protection" from "emission and other negative powers." This is a load of hooey, of course, on multiple levels. 2 There's actually so much accumulated hooey in these claims that it would take a whole separate post just to dismantle them, but I'll stick the short version in a (long!) footnote instead and you can read, or not read, as you like. 3

Anyway. Cacti need to be watered in general, and Cereus peruvianus in particular seems to do well if I give it a good, thorough drenching in my shower4 when the soil has gotten pretty dry, or completely dry: in practice, with the 5 ½-foot plants in the first picture, this means about every week and a half to two weeks, and for the smaller ones it's closer to every two or three weeks – I'm more conservative about them because they're in plastic, and their soil mix is also (accidentally) heavier, so I'll let them dry out, and then make them sit for another week or so before I water, just to be sure. In the winter, this slows down in both cases, due to all sorts of things (less light, colder temperatures, semi-dormancy), so it might be twice as long between waterings, but even then, they still get water from time to time, and I don't tease them with little sips.

The other necessary cactus care item is light. Indoor cacti need as much direct sun as they can get, generally speaking, but you can't actually move them out into full sun as soon as the weather warms up. They're not expecting that intensity of light, and it will bleach, scar, disfigure, or kill them to experience it all at once. Seriously. Indoor light and outdoor light are entirely different ballgames. Not even ballgames. I think one of them may be hockey.

Cereus peruvianus at work, photographed during a pirouette.

That said, if you have enough light for them, they're not terribly difficult. Given proper care, they're also quick-growing, which is a plus for me, though it wouldn't be for everybody.

I also appreciate that they're not spiny in every direction: when I'm taking the tall ones to the shower, I kind of have to hold on to the plant itself, somewhere, lest the plant start to tip and then smash itself into a wall. With some cacti, that's not really possible, but Cereus peruvianus has relatively minor spines, in fairly avoidable spots: I can grab either side of one of the ribs between thumb and forefinger and off to the shower we go. Easy care, relatively painless, quick-growing, and - you should see these babies dance.


Photo credits: all me.

1 A lot of cactus species naturally have white, slightly fuzzy spots near the areoles (the spots where the spines emerge), which makes it really easy to miss the presence of mealybugs, especially if you've been searching for the plant in question and are all adrenalized over having finally found one. As mealybugs and cactus go together like toast and . . . something that goes really, really well with toast, it's important to check these things.
2 Actually more like a hooey split: three scoops of hooey, on top of a flim-flam cut in half, served covered in snake oil and sprinkled with bullshit.
3 The central argument here seems to be the three-part claim that: 1) Cereus peruvianus specifically, 2) absorbs radiation emitted from cathode ray tubes (the newer liquid crystal displays, and other new types of displays, don't really emit anything dangerous and are therefore irrelevant), 3) which would otherwise reach you and cause you harm.
2) is true, but it's equally true of anything else: a piece of tissue paper, a coffee mug, a can of creamed corn, a corpse – all of these also absorb radiation. 3) is debatable, but plausibly true: cathode ray tubes, especially older ones, are capable of emitting some x-rays along with light, heat, and other kinds of radiation. Whether these are produced in large enough amounts to be worth worrying about, I'm not sure (I doubt it), but the most damaging, high-energy rays aren't going to be stopped by anything short of a few inches of lead, and putting a few inches of lead between yourself and your computer monitor sort of defeats the purpose of having a monitor. 1) is plausible, but I couldn't find any actual evidence that anyone has tried to test this, and the one sort-of reference I found just said that it had been found ineffective. It's plausible because, in theory, a plant that accumulated heavy elements (lead, thallium, mercury, gold, bismuth) from the environment would be capable of blocking radiation better than nothing at all, heavy elements being, generally, better blockers of radiation right up until you get to the really heavy elements, like thorium and uranium and plutonium, which are radioactive and therefore sources of radiation. Again, though, with our hypothetical bismuth-concentrating cactus, we have the problem of trying to read your monitor through a plant.
The claim is typically that placing the cactus next to your monitor will reduce radiation, but any radiation going out the side of your monitor was never going to affect you in the first place, and anyway if you're worrying about all radiation in every direction, your best bet would be to quit screwing around and encase your monitor in concrete already. At the very least you should surround it with lots of Chinese-made toys.
4 Like I do with all of my plants except one Cordyline: it's huge on its own, and in a massive clay pot, which is huger, the combination of which makes it more or less unliftable except for extremely special occasions.


Aiyana said...

I had not heard the radiation absorption theory before. Those who say this must be distorting some obsure fact--sort of like those magazines near the checkouts in grocery stores.
The C. peruvianus can reach 30 feet tall, so you're going to have quite a job carrying them to the shower!

Anonymous said...

The best way to combat Mealys is to use a systemic insecticide that includes imacloprid. Beyer Rose insecticide has this chemical in some of their formulations.

As far as the names go, cacti are still going through a lot of reorganization and renaming. Cereus peruvianus is as good a name as any. The common name is San Pedro. It is also called Tricocereus or Echinopsis peruvianus. A good article about this plant is here:

This cactus also contains alkaloids which have been used by natives and/or hippies as a hallucinogen. YMMV! Perhaps eating the plant makes one feel as though you can repel microwaves with your mind. I can't say, never tried it. I believe they have to be fairly large to flower. When they get lots of sun, they branch heavily.


mjazzguitar said...

I have some like the one doing the pirouette.
Some say it is Cereus Peruvianus Tortuosa.
I had to cut them back because they were getting to big. The funny thing is, some of the new growth looks like the tortuosa and some just grow straight like the regular column cactus.
This is the second time I have heard of imacloprid, I'm going to have to give that a try, because mealy bugs seem to be impossible to get rid of.

Raty said...

I have recently purchased a 2 meter cereus peruvianus. I am putting in indoor, with plenty of indirect sunlight (whole wall is glass), but no direct sunlight. Do you think it will do ok? How much should i water it?

mr_subjunctive said...


Those are sort of impossible questions to answer in a useful way, because there are so many variables involved besides just the amount of light.

I think probably a whole wall of indirect sun would be sufficient to keep the plant going; I've had C. peruvianus get by on less. You can watch the plant for feedback to see how it's doing: if it's not getting enough light, it will either not grow at all for a year at a time, or it will produce very thin, weak, stretched-out new growth.

Watering is covered in the post. Water when the soil is dry, water thoroughly and let the soil drain, never make the plant stand in its own drainage water. This will probably mean you'll have to check every couple days for a while, to see whether the soil is dry or not, before you start to get a sense of how often to water. If you're unsure whether the soil is wet or not, wait a few more days and check again.

Raty said...

Thanks for the reply mr_subjunctive :)
The cereus is 3 meters away from the glass wall.
I will watch the feedback you reccommend.
Its in a cement pot, does that have enough drainage?

Thanks again!

Raty said...

What about putting an indoor grow lamp on top of the cactus to mimc the sun and to help the plant keep growing upwards (and not leaning towards the light)?

mr_subjunctive said...


The composition of the pot has no bearing on whether the drainage is adequate. The composition of the soil matters a little bit (you want something that won't absorb a lot of water in the first place, and that will lose what water it does absorb fairly quickly: mixes low in peat and high in coarse sand or fired clay are preferable), and whether or not the container has holes in the bottom for water to exit matters a lot. Matters so much that I wouldn't even try to grow a cactus in a pot that didn't have drainage holes.

Oddly, my experience with C. peruvianus has been that they're not very phototropic (inclined to lean in the direction of light) in the first place. It may nevertheless be a good idea to rotate the pot about 140 degrees every couple months anyway, but it's not something I'd worry about a lot.

Supplementary light could help, but the lamp would need to be either very bright or very close in order to add a significant amount of light. Moving the plant closer to the wall would probably do a lot more for it a lot more easily, if that's possible.[1] It's also possible, in a lot of cases, to convince a plant to accept a bad location by moving it to a good location periodically. If there's a bright spot in your home that gets some direct sun and could accommodate the cactus, moving it there for a couple weeks every couple months and then returning it to the darker regular spot could give it enough light to keep it growing properly.

Supplemental light is unlikely to hurt anything: worst case scenario is that you use unnecessary electricity. I don't think you probably need to add lighting, though, unless the walls, ceiling, furniture, floor, etc. are dark and it's impossible to get the plant any closer to the wall.


[1] Light intensity changes as the square of the distance. This means that if you move the plant to 1.5 meters from the wall, it will receive four times more light than it gets at 3 m. Move it to 1 meter from the wall and it will get nine times more light than it gets at 3 m.

Raty said...

Thanks again for such a comprehensive reply.

I thought the cement pot, as it is a porous material, drains well. Should I change the pot? (Maybe to a geotextile pot)

I will find out which type of soil it has and see if I can change it for a coarser one.

Lightning is very bright in the apartment, walls are white, so maybe I can get away with no extra lightning. I will purchase some wheels to move the cactus closer to the window when im not home.

Thanks for everything again! :)

mr_subjunctive said...


I wouldn't change a cement pot with a drainage hole, but I would absolutely change any pot that didn't.

It's possible that cement wouldn't be a good material for some kinds of plants (I think there's some chemistry involved that makes cement better for plants that prefer more alkaline soil, though I haven't researched this so don't take it as gospel.), but I'm not aware of any reason it would necessarily be a problem for desert cacti.

Unknown said...

Do you ever get scale on your cactus? I never had a problem with this until the last few years. Dull grey spots that I can scrape off with my fingernail or a wooden popsicle stick. Some columns were so bad I just lopped them off and threw away. It started with low light issues and the trees have since beeen cut back. What to do? Alcohol? I’ve had the ‘momma’ cereus since 1976. I have been giving away cuttings for years. A friend in Albuquerque has hers flower profusely every summer. Huge, hand sized flowers. Mine, nada. And I have 10 mature columns now!


mr_subjunctive said...

Yoanna Baumgartner:

I have seen scale on Cereus, though it's been so long ago that I can't remember whether I've ever had any on my own personal plants. (I definitely remember mealybugs, which are very closely related to scale.)

I hate to suggest it, but to get rid of the scale, you probably need to treat the plant, and any plants nearby that might also harbor scale, with a systemic insecticide like imidacloprid: nobody's eyes are good enough to get every individual insect off of a plant as large as you describe, and trying to remove insects by hand generally only works on plants that are very tiny or infestations that are very new. Even a systemic pesticide won't necessarily be successful, but it's the only thing that has ever worked at all for me.

The bad part is that imidacloprid kills lots of different insects, not just scale, and is kind of an environmental problem, and because it's used against lots of agricultural pests, it's only a matter of time before some of them develop resistance to it. So if your plants will be outdoors during treatment, and especially if they're planted directly into the soil, I'd advise against imidacloprid even though it's the remedy most likely to work.

If you don't want to or can't use a systemic, it's possible that something like neem oil could work, but neem oil 1) smells very weird, if not bad; 2) will need to be reapplied repeatedly for at least a couple months; and 3) may or may not be a problem for the plant on its own. (Some plants are touchy about oils. I don't think columnar desert cacti are normally among them, but when I've tried spraying with oils, sometimes plants have dropped most of their leaves, or all the flowers and flower buds, or the oil left permanent marks on the stems.)

Spraying with rubbing alcohol before spraying an actual insecticide is supposed to be helpful; I don't know of any science to prove that, but the theory is that rubbing alcohol can partly dissolve the protective waxy coating on scale and mealybugs, and make it more likely that a sprayed-on insecticide can penetrate it. Given the size of the plants you seem to be talking about, I suspect that it isn't practical to spray rubbing alcohol everywhere and then spray something else, but it's still an option to consider.

You could also look into biological controls -- my personal experience with biologicals was very (very!) disappointing and expensive, and I'm not aware of anything that controls scale specifically, but probably there's something. I mean, something has to eat scale in the wild.

Sorry this isn't more encouraging, but scale is a difficult problem and doesn't really have good, easy solutions.

Unknown said...

Thanks for the comment. A systemic pesticide is out of the question for me. Besides the scale and mosquitoes, I like most of the other bugs around my yard! I’ll try alcohol and neem oil on one of pots that has fewer columns. I don’t mind taking the time, it would be great if there was something harmless to put in the soil to make it unpalatable to the scale.