(This is the sixth and final plant profile in the Wizard of Oz series.)
I find Adenium obesum a frustrating plant to have to deal with. It's not so much that they're difficult to keep alive -- as far as I can tell, so long as you don't overwater them, they'll stay alive -- as that they're just absurdly easy to frighten. Which raises the question, how do you know when you've frightened an Adenium? My answer: when it drops all of its leaves. And how often does that happen? Pretty much constantly.
I have more experience with them at work than I do at home; the one time I've attempted them at home thus far, the plant defoliated more or less as soon as it got through the door, and I got angry at it and threw it away. This was, I now realize, an overreaction: the plant probably would have come back if I had tried. (On the other hand, I can't say I regret missing the chance to have a leafless stump sitting around the apartment, either.) They've been bigger frustrations at work, though.
We got a batch in in June that were in really magnificent, full bloom. Some had light pink flowers, some had "red" (really more of a dark hot pink) flowers, they were all leafy and healthy and awesome. So WCW and I were like, gosh, these'll sell like hotcakes, let's put them up toward the front so everyone will be able to see them.
It was a good idea in theory, but of course they all lasted about a week and then started throwing leaves and flowers and buds all over the place, necessitating a clean-up and a hasty move to a less accessible part of the greenhouse. We waited for them to get their act together, which took a few months, and then when they started blooming again, we moved them back. Almost immediately, they got spider mites (and probably also overwatered), dropped all their leaves, and went back to the back, out of the main sales area, where they've been since.
So, you know, if Adeniums drove cars, they'd all have this bumper sticker:
Outdoors in warmer climates, it's a different story: people keep them outside in pots, and not only do they do fine there, but they bloom continuously (or nearly continuously), and everybody loves them and thinks they're the bestest, most perfect plant ever!1!1!!!1!eleven!11!1 Greenhouses are apparently not acceptable substitutes, though.
As far as sales go, well, they sell pretty briskly when they're in bloom and everything. Of course, then there are questions to be fielded from customers about why their plant defoliated, and what they're supposed to do with it now, and sometimes that gets awkward. I understand, of course, having been there myself, and I try to sound reassuring and let them know that this is not necessarily a big deal, the plant's just gone dormant, and yes, it will resprout again in the spring, and yes, it can still flower, and no, I understand that you wanted more than just a stump, and so forth.
The crashes aren't even inevitable. If you provide your plant with the appropriate, Florida-level amount of heat and light (and maybe also humidity), you can keep yours going all year long, so long as you don't do anything to startle it in the process. But, you know -- try explaining to a customer that they can have their flowers year-round only if they invest in a bunch of lights and heaters and extra equipment. They lose interest quickly.
On the other hand, I didn't realize until I started researching for this post that these are also crazy popular. I mean, we're talking, Hoya- and Saintpaulia-level popular. People loooooove Adeniums. Clearly not everybody minds having a part-time plant.
This means, of course, that since I've already tipped my hand about not liking them much (it was #5 on the worst houseplants list), and since there's a lot of conflicting information about them out there (it's not like with the Saintpaulia profile, where there was a lot of information but it basically all said the same thing: everybody thinks they know the best way to grow Adeniums, and nobody does it the same way as anybody else), anything I say is going to be disagreed with by a ton of people, a situation to which I am quietly resigned. You can find other perspectives at mrbrownthumb or Water Roots.
For me personally, I find them disappointing. Some of this, I'm pretty sure, is that I was somewhat misled about what to expect from mine, but even had I known about the dormancy thing, dormancy's not supposed to begin in August. And pests (spider mites in particular) are a problem regardless. So no, I don't recommend this plant, particularly not if you're looking for something permanent, for a spot indoors. I'll give you the best information I've got anyway, and you shouldn't necessarily take my experiences to mean that you can't or shouldn't make an attempt if this is a plant you really want to grow. Everybody else says it's easy, actually. It's just that, you know, it's not necessarily going to be all pretty flowers and shiny green leaves.
Adenium as a genus is from East and South Africa, plus a little bit of the Arabian Peninsula. In fact, the name itself comes from the Arabic name for the plant, Oddaejn, which means Aden, with Aden being the old name for Yemen. Common names range from the cynically salesmanlike ("desert rose," "mock azalea") to the obscure ("Sabi star") to the ridiculous ("impala lily," "kudu lily"). It is of course not related to roses, azaleas, or lilies (to say nothing of impalas or kudus), and is actually in the Apocynaceae, the family of Nerium oleander, Plumeria spp., Pachypodium spp., Mandevilla spp., etc., which family I discussed at boring length in the Pachypodium profile, q.v.
Specialists disagree about how many species are in the genus: one (kinda extreme) school of thought is that obesum is the only species, and the variability of the plants around the continent (and they are highly variable, differing in size, flower color, and general trunk shape) merely points to the existence of a lot of subspecies. The opposing view is that different populations are different enough to count as separate species, and the taxonomists in this camp have assigned a variety of other names to these plants (Adenium arabicum, boehmianum, multiflorum, obesum, oleifolium, socotranum, somalense, and swazicum).1 Depending on who you know, you might be able to get hold of a plant by one of these names, but it may or may not be an actual species. Care should be at least mostly the same, regardless, as these are all from similar climates.
Adenium obesum is grown both for the flowers and for the sculptural,2 thickened trunk. The trunk is an adaptation for storing water during the prolonged dry season (or, in some cases, the habitat is just dry all the time, and there's not really a wet season and dry season, in which case it's for storing water whenever there's water to store). The roots are also thick: they disturb me in kind of the same way that Buddha's-hand citrons disturb me. (See a picture at davesgarden.com.)
The flowers are the main draw, though, and may appear at pretty much any time of the year, as far as I can determine: I don't think there's been any point between June and December when we haven't had at least one flower going at work (though the smaller, 4-inch plants are far less likely to flower, in my experience), and they are supposed to be perpetual bloomers when grown in warm climates. Indoors, of course, they're not going to bloom during dormancy.
So how are you supposed to take care of one, then?
LIGHT: Indoors, you want full sun. Period. In fact, outdoors, you want full sun, too, probably, though people do manage to grow them in outdoor shade. If you don't have full sun indoors, don't bother. Seriously.
WATERING: The general rule of thumb indoors seems to be to treat these like a regular tropical plant in the summer, like a funny-shaped smooth rock in winter, and ramp up watering in the spring and bring it back down in the fall. Some people who grow Adeniums don't water at all between October and April, and this works, I'm told, just fine.
They also need very lean soil, with very little capacity to retain water. This is not so much important during the summer (although they can be overwatered to death in the heat of the summer, it doesn't seem to be common), but in the spring and fall, it's a big deal. (In winter, you're safest not watering at all, though it's unlikely that anything bad will happen if you water once or twice. The catch is that if you water, the plant is going to try to come out of dormancy, so don't wake it up until the conditions are right to grow it, or else it'll just wake up, look around, grow a couple leaves, and then panic and drop them.)
It's also probably a good idea to use a clay pot, instead of plastic (clay dries out faster), and if you're offered the option, a deeper pot is better than a shallow one: the roots go down further, and get larger, than you'd think. Younger plants usually need fairly frequent repotting, and have been known to break old pots if they didn't get a new one quickly enough. As a general rule, repotting is a spring-only deal: repotting in fall or winter is likely to end badly, and repotting in summer might be okay, but it didn't work out so well with the one I bought, so I hate to recommend it.
HUMIDITY: Mostly irrelevant to the plant, though higher humidity may help keep the spider mites at bay.3 Dryer air might be preferable during the winter -- the less moisture, the less risk of rot, is my logic -- but if you're like most people, dry air isn't something you'll have to work at, and it's not necessarily helpful. Don't sweat the humidity, is the gist.
TEMPERATURE: Heat is not a problem at all. They actually seem to really like heat, and can handle temperatures at least into the 100s F (38-43C) with no problem. Cold is another story. Different websites give really different information, but it appears to me that about 50F (10C) is as low as you can go and be completely safe. Plants will sometimes survive light, brief freezes but will probably lose branches in the process (and frost-damaged branches can provide an opening for rot, so surviving the freeze itself doesn't guarantee that the plant will make it). If your plant has been accidentally frozen, there's a decent chance that something might be salvageable, depending on how cold, how wet, and for how long.4
PESTS: So far, the only pests I've witnessed have been spider mites, which unfortunately can develop into huge, writhing balls of mites so quickly that it's not uncommon to hear a sonic boom, as the growing sphere of mites begins to expand faster than the speed of sound.
That may have been slightly overstated. But only slightly.
They are also attractive to the oleander caterpillar, which as you can guess from the name is a caterpillar that mostly feeds on Nerium oleander.5 Caterpillars are really only worth worrying about if you leave your plant outside for part of the year, though, and they're killed by cold weather so they're not normally found north of Florida anyway. Mealybugs are also a concern, according to a commenter at the davesgarden.com page on this plant (scroll down to the comment by "CropDoc"). The same commenter advises against using insecticides on Adenium (Why? He doesn't say.), and recommends alcohol, applied by cotton swab, which sounds like a fun way to spend an afternoon.6 Then of course there's rot. And scale (for which the treatment should be the same as for mealybugs). And whiteflies.
PROPAGATION: I'm not sure where one would buy seeds, but Adenium obesum can apparently be grown from seed fairly easily, and seed-grown plants will develop the bulbous trunk from the beginning. Sometimes, plants will spontaneously produce seed pods as well, which are 8-12 inches long when mature and may contain 50-60 seeds. These are apparently very easy to sprout: most will germinate within a week. One can also take stem cuttings, which are apparently not that difficult either, though cuttings have to be allowed to dry and callus before planting and do not immediately develop bulbous trunks (I think they still do eventually, but I was unable to confirm this.). See mrbrownthumb for more detailed instructions on how to propagate Adenium obesum from cuttings.
It's common for the more interesting cultivars to be propagated by grafting cuttings onto the caudexes (caudices?) of more common varieties, because plants do not necessarily come true from seed. This is not likely to have any effect on the casual grower, though I can maybe envision a situation where a plant that was cut back could resprout new stems from the base, which would have the flower color of the stock plant, instead of the desired cultivar. Not terribly likely, though.
It's worth pausing to note that, like most (all?) of the plants in the Apocynaceae, Adenium obesum is poisonous in an especially hardcore and not-to-be-fucked-with way (hunters have used arrows coated with Adenium sap;7 if it can take down an antelope, it can knock you dead too). So be careful if you're going to try to take cuttings. One person at Garden Web reported that a friend of theirs worked in a nursery and sometimes had to handle large quantities of bareroot Adeniums, and that "he gets a metallic taste then nauseous just from touch[ing] so many, he now [wears] gloves when handling." So if you start to get a metallic taste in your mouth and feel nauseous, you should stop messing with the plant and go wash your hands, at the very least. Or you could just wear gloves to start with.
GROOMING / SPECIAL CARE: Well, you'll need a broom.
The most special special-care issue with Adenium is learning how to manage the annual cycle: when to start easing back on the watering, when to start watering again, and so forth. This is difficult stuff, though the penalty for getting it wrong is not that bad, and basically amounts to -- you guessed it -- defoliation. Getting it really wrong results in rot, which is more of a problem, obviously, but also less likely.
During the research, I ran into some people asking if there was a way to promote caudex growth. The advice they were given (in this Garden Web thread) was to plant the plant a little bit higher with every repotting (only about an inch), so that over time the roots are gradually raised out of the soil. Judging by the spectacular picture at that link, this is a good way to get an impressively twisted plant.
Plants are said not to get significantly taller after a few years of growth: if you want a tall plant, you have to get it tall while it's young. After that, they mostly just get wider.8 Species other than obesum can get to be tall, though (ten feet is not unheard of).
FEEDING: The usual recommendation is to feed with a balanced but weak (20-20-20 at quarter-strength, e.g.) fertilizer with every, or at least most, waterings when the plant is actively growing. Some people prefer a couple full-strength feedings during the growing season.
When possible, it's probably best to try to obtain plants grown near your home, rather than going to a box store that's had them shipped in from across the country. There are two reasons for this. One, shipping is fairly traumatic for the plants. The plants we got in at work dropped all their flowers and a good chunk of their leaves all at once not so much because of the move itself, but because of how the move was done: in that particular case, I think the plants were watered, wrapped in brown paper sleeves, loaded into cardboard boxes, and then stuck on a truck for three days. You'd be scared too. (It's a wonder they didn't rot.9)
Two, the interests of the grower and the interests of the consumer do not necessarily overlap. Just before I started writing this post, I e-mailed Cactus Blog to ask just what the hell it is that Adeniums want, and why they're such a pain. Peter was kind enough to e-mail back, and his advice was incorporated into the above care instructions, mixed with various bits and pieces I've gathered from elsewhere on the web. But there was one thing I didn't see addressed anywhere else. Peter:
. . . the key problem with most adeniums you'd get in are that they're pushed in greenhouses to bloom, and they grow what we take 5 years in 1 year or so. So they're not healthy to begin with.
You'd expect stressed-out plants that are pumped full of steroids10 and made to grow faster than they naturally would to sell about as well as plants that are grown in a slower, sturdier fashion, and obviously they're going to take much less time and work to produce, so you'll get them cheaper, too.11 The catch is that such plants may also have a much tougher time adapting once they get to your house, and so you might wind up losing more plants, having to work harder to keep them alive, getting weird-shaped growth as they adapt, or etc. If at first you don't succeed, try, try again with a plant from a different establishment. Or the same establishment at a different time, possibly.
I don't know that I'll be retrying. I try to avoid plants that are exceptionally mite-prone (though there are some grandfathered exceptions, the main one being Cordyline fruticosa), and plants that I have had bad prior experiences with, both of which apply here. And I'm also leery of anything that's semi-deciduous (I even worry a little about Ficus benjamina and F. religiosa.). So the odds don't look good. But I've changed my mind about plenty of plants before, and I imagine these will be especially tempting when they start blooming again, whenever that is. We'll see.
References: species/subspecies designations from University of Wisconsin. Origin of name from valentine.gr. Poison-arrow Euphorbia species ID from African Ethnobotany.
Photo credits: Cowardly lion via shawnnacox.com; plant photos are my own.
1 Please don't feel obligated to care, but: Tropicos, which I had somehow neglected as a resource until reminded of its existence by exoticrainforest.com, lists arabicum, arboreum, boehmianum, cotaneum, honghel, lugardii, multiflorum, namaquanum, obesum, oleifolium, socotranum, somalense, speciosum, swarzicum, swazicum (possibly a typo of swarzicum, or vice-versa?), and tricholepis, plus several subspecies of obesum, some of which overlap with the species listed, e.g. Adenium socotranum and Adenium obesum var. socotranum.
2 "Sculptural" in the Henry Moore sort of sense.
3 There's some confusion on this point, as I've seen it said that humid air can actually make mite problems on Adenium worse. Might have been a typo, though. This isn't beyond the realm of plausibility, but it's not the usual way of things: generally, mites like hotter, dryer air.
4 In fact, if you want to see a flame war erupt over the proper winter temperature for Adeniums (and who among us doesn't?), check out this Garden Web thread. It's pretty incredible. It's also, in the end, fairly unilluminating, and ends without any obvious victor, so the question remains unanswered. In general, I find that when people who have obviously grown the plant in question disagree about its care like this, it usually means that either method is acceptable, and the debaters have just had different experiences for some reason or another. Only rarely is somebody just plain wrong.
5 Not particularly surprising, as Nerium oleander is a close relative of Adenium obesum. For more on the oleander caterpillar, interested readers should check out Wicked Gardener.
7 Interestingly, or maybe not interestingly: the hunters who do this don't use the Adenium sap by itself, but mix it with the sap of a Euphorbia, and sometimes many other ingredients. The Euphorbia in question is one I'm not familiar with (E. subsala), and appears to be more a thickening agent and adhesive, as opposed to being an active ingredient.
8 (Like people!)
9 They shouldn't be sending us specimens of rot-prone plants right after watering them, of course. My guess is that plants in Florida heat either have to be watered so often, or get rained on so much, that any plants the grower picked would be at least somewhat wet at any moment. This is not good, and it's caused us problems before, but there's likely nothing that can be done, really, and I can't say we lose a lot of plants to it: it just makes me anxious.
10 Metaphorically speaking: it'd actually be fertilizer and maybe the occasional hormone, not steroids. I don't think giving plants anabolic steroids does anything for them, and it certainly wouldn't make them grow bigger/faster/musclier.
In one sense, though, Adeniums are probably already pumped full of steroids: I couldn't track down a structure or even a definitive name for the toxin(s) in the plant, but they were often compared to digoxin, the toxin in Digitalis (foxglove), which does contain the particular arrangement of carbon atoms called the steroid nucleus: three six-membered rings and one five-membered one, arranged just so (ignore the numbers):
This particular arrangement shows up all over the place in nature, with other atoms attached to it, in everything from cholesterol to testosterone to yams to poison-arrow frog venom. So technically, Adeniums're already full of steroids, just not the ones you were probably thinking of.
11 As I am occasionally reminded at work, plants cost us money even if they're just sitting there, not doing anything: they have to be heated, fed and watered, none of which are free, and then also people have to be paid to watch them.