Those readers who only look at the plant profiles for the sake of finding interesting and weird plant-related trivia, I'm going to do you a favor and give you the weirdest stuff up front. My new favorite piece of houseplant-related trivia of all time, replacing my Calathea-related favorite from a couple years ago,1 is this: Aloe vera gel, the liquid taken from the centers of Aloe vera leaves, is sometimes used to dilute sheep semen. (Let that sink in for a second.)
You may ask, Why would anyone ever want to dilute sheep semen?
[pondering]
Well I think the real question is why wouldn't you want to dilute sheep semen. What the fuck are you going to do with concentrated sheep semen?2

I don't know why knowing this tickles me so. Perhaps it's just that it was so unexpected. Aloe vera has been used in a lot of different ways through the ages, so I suppose I maybe shouldn't have been that surprised, but . . . well, you know, I wouldn't have thought of overly-concentrated sheep sperm as even being one of the world's problems, much less anticipated that Aloe vera might be the solution.
But so now that we've gotten that out of the way, let me introduce you to Aloe vera.
The first thing to know is that it's sometimes called Aloe barbadensis, and in fact I've been calling it that for the last couple years, because I thought the name had been officially changed. It wasn't until I started researching this post that I found a lot of places, including some that have a lot of credibility with me, like GRIN and davesgarden.com, calling it A. vera. As I didn't come across any explanations for why the name change or any definitive answer on which was correct, and as vera is more familiar to most people and marginally faster to type, I'm going with vera.
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There are a lot of things sort of like that about the plant, though. Not only does it have two more or less interchangeable names: the good, pure, familiar vera ("true") and the more difficult, scientific, weirder barbadensis ("from Barbados"), either of which could be correct at any given moment, but we also don't know where it came from, or even whether it's a species at all, originally. Coleus (Solenostemon scutellarioides3) has name-change and obscure-origin problems too: these things happen.
The prevailing theory, as far as I can determine by reading around, is that it originated along the north coast of Africa4 and was spread around all over the place by humans. There are some indications that it may have started out as a hybrid, too: it has certain strong genetic similarities to a handful of other Aloe species that are mostly from northeast Africa.5 Whatever its origin, A. vera now grows pretty much anywhere in the world that's warm and dry enough for it, including Hawaii, India, Australia, Paraguay, South Africa, Jamaica, and southern Europe. Some of this is deliberately cultivated, and some is naturalized.
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Aloe vera in mass production, location unknown. Photo by sdm9093, found via Wikipedia.As with any even remotely medicinal-type plant, people have tried using
Aloe vera against pretty much every condition imaginable. In a lot of cases, nothing particularly useful happened, but there are two conditions for which
Aloe vera seems to be especially helpful, using the word "helpful" kind of loosely. Both use the leaves, but different parts of the leaves.
The bulk of the leaf contains a gel which is not only a great sheep semen diluent, but it also soothes and speeds healing of burns. This is the use most of us are most familiar with, and
Aloe vera's usual excuse for being in people's homes. It's also a mild antibacterial and antifungal, which has led to its use as an aquarium water additive, which is not quite as weird as the sheep semen but is pretty close. The aquarium thing doesn't appear to be widespread at all, though.
Aloe gel has also been used for all kinds of other skin conditions, and even quite a few non-skin conditions: as far as I could tell from sifting through the information I found, there's not a lot of scientific support for using
Aloe medicinally aside from treating burns, and
Aloe products are not universally helpful when you're talking about burns. For example, although Big Aloe would have you believe that
Aloe vera gel can act as a natural sunscreen and prevent burns, this is not supported by science. (Try it for yourself, if you like.) It's also unproven for treating burns caused by radiation (X-Rays, radiotherapy for cancer, etc.), apparently, though I found many people willing to say otherwise, and the skin is too damaged in a third-degree burn for
Aloe gel to help much. Still, your normal household burn is likely to be just a first-degree, so they're worth having around.
The antibacterial action I mentioned earlier
has been scientifically demonstrated, and bacteria in petri dishes have died and everything, though it's not clear how useful that actually is in real-life situations. Tests on how quickly wounds healed when
Aloe vera gel was applied, for example, have given conflicting results. People also sometimes drink the juice to get rid of stomach ulcers (which are caused by bacteria), but again, it's unclear how much that helps.
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As for every other product that makes the claim, there's no evidence that rubbing
Aloe vera gel into your skin will reduce wrinkles and make you look fifty years younger, but you probably already suspected that.
There's such a long list of other health problems that
Aloe vera has been used to treat that I'm going to stick it in a footnote. I do not necessarily encourage or endorse the use of
Aloe vera, topically or internally, for any of these conditions. People have tried it, but that doesn't mean it worked.
6Basically everybody recommends that pregnant women or nursing mothers not use
A. vera products; pregnant women shouldn't because it can trigger contractions and miscarriage, and nursing mothers shouldn't because it's not known if any chemicals from the plant are expressed in breast milk, or how it might affect an infant if they were.
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There's a second, somewhat less pleasant, main use, from the layer of cells just underneath the surface of the leaf, though, which contains a bitter yellow chemical called aloin.
7 Aloin, taken internally, is a laxative. It basically irritates the lining of your colon so that it contracts more often and harder, pushing everything along faster, and at the same time it interferes with the body's ability to reabsorb water from the intestines. So, once everything's been pushed to the appropriate place, it's a lot wetter (and therefore softer) than it would otherwise be. If everything works the way it's supposed to, that is. If you overdo it, you wind up with painful cramping and diarrhea, which would be a
strong incentive not to overdo it.
However! The U.S. Food and Drug Administration prohibited production of over-the-counter laxatives containing aloin in 2002, due to concern about its safety and the potential for side effects.
8 They still permit its use as flavoring (for certain alcoholic drinks; I don't know which ones), or in "herbal supplements," which is just a tiny, tiny taste of the reason why the whole herbal supplement market in the U.S. makes me really uneasy.
9 Other species, including
A. ferox (also sometimes grown as a houseplant or garden succulent), also contain aloin, and in the past, they were also used in its manufacture. People also occasionally drink
Aloe vera juice, either on its own or mixed with other juices, and although these products don't use the aloin-containing layer, trace amounts of aloin may be present in the final product; heavy consumption of
Aloe juice can lower blood potassium to dangerous levels, among other things, though I'd think you'd have to be trying pretty hard to give yourself that kind of problem.
A few remarkably unlucky people also find their skin irritated by
Aloe vera, specifically the yellow aloin-containing layer, and get rashes and stuff. (Which is too bad, because you know what's really good at clearing up skin irritation?)
So the plant does have some legitimate health-sustaining credentials, but you don't want to go throwing it into everything all willy-nilly just because it's Natural and therefore Good For You, because it's got a bit of a dark side too.
Note the leaf in front with the brown line on it where it touches the pot. This will be important later.The appearance of the plant is also a bit two-faced. Maybe even three-faced. Very young offsets are usually green or blue-green with white spots, with leaves arranged in two stacks opposite from one another. As they age, leaves remain spotted but start pointing their leaves in all directions, forming rosettes. This middle phase is how plants are usually sold. At some point after
that, if they're happy, there's a second transition when they lose the spots and become huge. This confused me once at work; someone brought in a plant they said was an
Aloe vera, in a big pot, but it didn't look like one to me -- it was much too big, didn't have spots, and was yellowish-green instead of bluish-green. The yellow-green was explainable if it had been getting a lot of sun;
Aloes frequently turn reddish in bright light. But I didn't actually believe it was an
Aloe vera until a few months later, when it flowered (yellow, tubular flowers on tall stalks) and I was able to check the flowers against the internet, and then it produced offsets which were obviously
Aloe vera offsets, so I became a believer then.
A few sites call the spotted and non-spotted forms distinct varieties of the plant, but they're obviously not stable varieties, since one changes into the other over time, see the above picture.
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Care for
Aloe vera is pretty straightforward succulent-plant care, nothing terribly tricky:
LIGHT: More is better, and ideally full sun, but plants can get by on less if they have to. One of my plants is in a filtered sun / bright indirect spot in the plant room, and has been doing fine with that. It's maybe not growing as fast as it would like, and it's not as blue as it would be in brighter light,
10 but it does fine. The others are under very bright artificial light, and do well there. They're equally flexible outdoors, though in full outdoor sun the leaves will redden. This is normal, and will go away if the amount of light drops. Plants that have been grown indoors in lower light will sunburn if suddenly placed in bright outdoor sun.
Aloe vera as an outdoor ornamental. The original photo is by Wouter Hagens and is public domain; I've cropped and resized. Via Wikipedia.WATERING: Typical succulent watering. Use a fast-draining, fast-drying gritty potting soil. Drench the plant, then wait for it to get completely or almost completely dry, then drench it again. In the winter, water less often, or not at all (see
TEMPERATURE and
PESTS).
TEMPERATURE: Outdoors,
Aloes can handle brief light freezes --
sometimes. Accounts vary. It looks like once you go below about 50F/10C, the odds of a plant surviving start to drop, particularly if the soil is also wet, hence the need to water less in the winter.
I'm not aware of any upper limit on temperature (they are from northern Africa, after all), though I assume there must be one, and one person in the comments at davesgarden.com said that they're more prone to root rot if watered when it's hot. This doesn't make a lot of sense to me (Northern Africa! When would it
not be hot?), but I don't have any actual personal experience on the matter, so I suppose it could be true. If you can stand the temperature, your
Aloe probably can as well.
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The gel is said to lose potency when heated or exposed to air, and doesn't store very well as a result. This probably doesn't matter to you if you're just breaking an occasional leaf off of your plant at home to treat burns, though it might make a difference in how you should store products containing
Aloe vera.
HUMIDITY: Not much of an issue for this plant.
PESTS: Not especially prone to pests, though scale and mealybugs are always possible. Root rot is also a common problem, if plants are too wet, particularly if it's also cold.
PROPAGATION: Plants will eventually self-propagate through offsets. Although the plant used as the example is actually an
Alworthia,
11 not an
Aloe, the basic procedure from
this post works just as well for
A. vera; I've done it myself.
The impression I get from the way people talk about them, and from my own personal experience, is that a plant's inclination to offset is mainly a function of how much light it's getting. Outdoor plants in warm climates are said to be practically a pest, they offset so much. My indoor plants under fluorescent lights have started to offset a little bit, despite still being babies themselves; the one in the plant room, getting less light, hasn't offset at all.
GROOMING: Not a lot of grooming to be done. I find that occasionally leaves will develop flattened sections, especially near where the leaf rests on the edge of a pot. Once that starts, I'm not aware of anything you can do to reverse it, but it will eventually spread across the width of the leaf. Sometimes it stays like that, and sometimes it dries out and turns black and brittle, at which point you can pull off the end.
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I don't know specifically what causes this, but my suspicion is that it must be mechanical injury: the ones that get moved around most seem to be most prone to doing it, and often it begins where leaves touch their pots, which suggests that there must be something special about that spot. Bruising is all I can think of. If anybody has a different theory, I'm all ears -- none of the research even
mentions this, never mind explaining it. (
UPDATE: Oh. Actually
one of them did. It says that black spots on the leaves are caused by overwatering. We might be talking about different kinds of black spots, though.)
FEEDING: Normal houseplant fertilizer, according to label directions, though you can skip winter, especially if your plant is going to be in a cold spot. They don't exactly go dormant -- if you have a spot that's warm year-round, they'll grow year-round -- but if it's cold enough, you won't be watering that much anyway.
There aren't any cultivars of
Aloe vera as far as I could find, which is kind of surprising. I mean, you'd think with a plant that's been cultivated for thousands of years would have accumulated some interesting or pretty mutations, but if they're out there, they hide well.
Aloe vera is also one of the plants which have been tested for their ability to remove volatile organic chemicals from air. I'm not terribly impressed by this (I suspect that if you tested the species used as houseplants, you'd find that they
all clean air to some degree or another), but some people are, so I mention it.
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I remind the reader also that
Aloe vera will be useful during
the zombie apocalypse, mostly for those whose zombie-proofing includes flamethrowers. And even without zombies,
any apocalypse is going to be hell on the skin. Can't hurt to have a couple
Aloe veras around. More than that, you'll be prepared if there's a sheep semen apocalypse.
12 I can't quite visualize what a sheep semen apocalypse would look like, though the parts I
can imagine are very disturbing indeed. It's definitely not the kind of thing you want taking you by surprise.
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Select references (The list of everything I looked at, whether I used it or not, would be too long and pointless, and would include a lot of advertising for beauty care products that don't deserve free advertising.):
Wikipedia (Aloin)
Wikipedia (Aloe vera)
Memorial Sloan-Kettering Medical Center (Aloe vera) (medical/technical)
Poisonous Houseplants (aloin)
ILoveIndia.com (questionable info about medicinal uses)
Zanthan Gardens (blog post about outdoor Aloe vera flowering in Austin, TX)
Guide-to-Houseplants.com (care)
FlowersInIsrael.com (mostly historical stuff I didn't use in the profile, but interesting)
PlantCare.com (care)
Davesgarden.com (comments are more informative than the profile)
Wignet.com (.pdf about a case of a woman who gave herself hepatitis with Aloe vera tablets "in the hope to delay aging")
University of Maryland Medical Center (medical/historical)
Photo credits: Mine except as otherwise noted.