Tuesday, July 28, 2009

How to Divide an Alworthia

As you may have noticed, I'm trying to do more how-to posts lately:

This is sort of the natural consequence of 1) not being able to rely on pictures from work for posts to the extent that I used to, and 2) not working also means that when I have to do stuff around the house, I'm a lot more likely to have the time to take pictures of the process.

So this particular task involves my Alworthia 'Black Gem.' I got it as a single little rosette in the mail, through a plant exchange in 2007, and in the two years since, it has grown into a tightly-packed bundle of plants, which is awesome.1 When this sort of thing happens, I want to propagate, because . . . well, because that's just what you do when you have an easily-propagated plant that grows well for you. I mean, what were my other options?

(Aloe and Alworthia cvv. vary considerably in their tendency to offset, by the way. Many of mine have not offset at all. This may be, to some degree, a function of how long I've had them and what kind of care I've given them, but at least some of the latter group are "tree aloes," which grow tall and branched, rather than producing offsets in low clumps. 'Black Gem,' 'Walmsley's Blue,' and 'Doran Black' are all good offsetters, though, and even many of the trees will offset occasionally.)

Anyway. So to divide a clumping Alworthia like 'Black Gem,' first you pull the plant out of its pot and assess the overall situation.

You can't really see it in the picture so well, but these are all connected to one another by thin underground stems. I didn't want to remove the soil to show you because I figured I'd be traumatizing the plant enough already as it was.

Separating the plants from one another is so easy I'm not sure how to tell you to do it. You just grab the base of one rosette gently and pull it away from the rest of the plant: that's it. Generally the daughter plant will come away with a bit of a root system already, though if it doesn't, it's not that big of a problem. You'll notice the one furthest to the left in the below picture doesn't really have anything you could call a root yet. It'll be fine.

From this point on, it's basically indistinguishable from repotting. You fill a pot loosely with dirt:

Then you stick your finger in to make a hole in the dirt:

Then you set the plant in the dirt:

Then you add soil as necessary and firm it up around the roots, so the plant stands upright on its own:

And then you're basically done. I personally water mine in afterward:

Watering in is slightly controversial, in that the usual recommendation is to, at the very minimum, wait for a few days before watering, and some people will even tell you to pot the plants up a few days after separating them, giving the plants time to callus over any wounds incurred in the process of separating them. I don't disagree with this, exactly, but I've also never done it, and I've never lost any plantlets as a result, as far as I can remember. (With Aloes, I'm much more likely to have a plant root and do well for several months, and then die when I overwater it during the winter.)

Certain things might make the callusing / delayed watering thing more necessary: if you're having to reuse old soil from a sick plant, or garden soil (you should not do either of these, but I know some people will anyway), then there's more risk of a fungal or bacterial infection, and allowing some time to callus will do the plant some good. It might also be worth waiting a day or two to plant and water if the plantlets didn't come loose easily: if you think you might have injured the plant a lot in the process of pulling the plantlets off, then by all means, wait.2

However, if you're using clean, sterile soil, as you ought to be, and the plantlets came free easily, your actual risk of rot is pretty minimal, and my experience is that there's no penalty for impatience if you're not cutting corners elsewhere.

Something that is very important is your soil composition. Not only should it be a clean, sterile, and loose mix, but you want to avoid soils that will retain a lot of water. This means no Miracle Gro, or any other mix that's mostly peat moss. Your mix needs to drain quickly, it needs to be permeable to air, and it needs to dry out quickly when it's wet and re-wet quickly when it's dry. Miracle Gro has none of these characteristics.3 I prefer Ball Potting Mix with a bit of Schultz Aquatic Soil4 mixed in to speed drainage up a little bit, though you can vary the recipe somewhat. With Aloes, any decent potting mix will work, ideally with a little coarse sand, aquarium gravel, or "aquatic soil." All it really needs to do is sit there and not rot, dissolve, or absorb water.5 Perlite, though it will absorb water, does a good enough job of allowing air into the root ball that it's also okay to use, though I still like my aquatic soil better.

Water the new plants cautiously. You should have been doing that anyway, because they're Alworthias, but it becomes even more important with freshly divided plants. I've also found it useful to use bottom heat and bright light while the plants establish: Aloe aristata x Gasteria batesiana offsets were the main beneficiary of the top-light-bottom-heat system I described in the post about my shelving set up, and the 'Black Gems' seem to be settling in very quickly already. I think I'm even seeing new growth already, even though I only did this a couple weeks ago.

This is fairly basic stuff, but it comes up often enough at places like Garden Web, so I figure there must be someone who wants to know.


DISCLOSURE: Mr_subjunctive was not compensated to endorse Ball Potting Mix or Schultz Aquatic Soil in any way, though if someone from Ball or Schultz wanted to cut him a check after the fact, he would totally deposit it. He would also accept a lifetime supply of either product. Ball, Schultz -- think about it, okay?

1 As discussed at some length in the Alworthia 'Black Gem' profile, I was not much of an Aloe fan, to begin with: I'd initiated the exchange because I wanted an Aloe variegata, which were (and still are) impossible to find in Iowa, for some reason, and I got a whole bunch of other Aloes thrown in for free. Some of these have worked out better than others: 'Black Gem' is one of the biggest successes, but A. maculata and A. greatheadii var. davyana have also done quite well, and A. 'Walmsley's Blue' is a monster. (In the good way.)
That fall, the husband found me a bunch of assorted succulents for my birthday, including the Gasteraloe previously mentioned, which I like so much it placed #5 in my Top 10 Houseplants list. So I've been forced to progress from a mere tolerance of Aloes and their relatives to actual enthusiasm for them. I even bought a new one, an A. vera, on Sunday. (I hadn't gotten one previously because everybody has them and I find them boring, but Lowe's had one on the sale rack for $1 and I couldn't pass it up.)
2 There are situations where it is important to callus a plant before sticking it in soil: if you're taking cuttings of certain cactus or Euphorbia species, for example, you probably need to do this. Some succulent cuttings will work much better if allowed to callus, too, like for example jade plants (Crassula ovata). I don't worry about callusing so much for plants like Aloe, Gasteria, Haworthia, and the like, because these all tend to be somewhat pre-divided: they usually already have some roots, the points of attachment to the rest of the plant tend to be fairly constricted and dry already, and so forth.
3 Well I'm sorry, but Miracle Gro is not particularly good stuff to use for indoor plants, whatever the people at Scotts tell you. It's a particularly bad choice for succulent plants like Aloes and Alworthias. The best mix I've found so far is Ball Potting Mix, which is what we used at work (and sold a lot of, too, as far as that goes). It's more or less perfect directly out of the bag for your average tropicals; for succulents and cacti I do like to amend it a little (keep reading).
I don't know that I necessarily endorse Ball as a company overall: no doubt they're as bad as anybody else. But I will buy their potting mix so long as they keep the composition and price the same, even if I find out it contains puppy blood, because it's really good.

Maybe I'm kidding about the puppy blood. But maybe I'm not.
Ball's product is not cheap, unfortunately: we were selling it at work for $22.50 per 79L bag (the size in the picture) when I left work. It's possible to get it cheaper than that, but around here you have to know people who know people (which I do) and make plans (which is harder), and I haven't gotten it together to do that yet. But then, with any luck, I won't need any more for a long time.
4 Schultz Aquatic Soil isn't what you normally think of as "soil" at all: it's basically just a bunch of pieces of fired clay, of more or less uniform size. It's outrageously priced for what it is, but as with Ball's mix, I will be loyal until presented with a better option, because it improves drainage very nicely, even in small proportions, and it won't add fluoride to the soil like perlite will, so it's safe for fluoride-sensitive plants like Dracaenas and Chlorophytum comosum. Prices vary a lot, and less-expensive substitutes may be available (I haven't ever really looked into it that much), but a bag this size will run you maybe $6 at Menards, if you're shopping at the right time of year and in the right store:

5 Not quite true, actually: it also needs to have a fairly large particle size. If the particles are too fine, as in very fine sand, they can pack together tightly and cut off air to the roots. So it needs to not rot, dissolve, or absorb water, it needs to be coarse enough in texture that it won't pack around the roots and kill them, and it can't break down immediately into something that will pack around the roots and kill them, either.


Xavi said...

you have a great blog

lynn'sgarden said...

Where was this post when I repotted my jade plant~honestly!! Of course I used the Miracle Gro! It was a beautiful 'tree' that lasted 4 years (which is 3+ yrs. over most my regular houseplant survival!)..I can cry thinking about it! And, yep, I have the commoner barbadensis aloe :) LOL..Ball should compensate you..how long does that big bag last anyway? Is there a picture anywhere in archives that show your apt. with the 500+ plants?? I would love to see that!! A great how-to post mr. subjunctive! Headache gone, I hope!

mr_subjunctive said...

I can't really say how long one of the big bags lasts, because obviously it depends a lot on how much repotting I'm doing. I bought three, I think, at the end of May when I was leaving the job, and two of those are gone now, but I've been doing a lot more planting, too, since the move.

Ball does have bags half that size and 1/4 that size, which are more manageable though slightly less economical.

I don't have any pictures showing much of the apartment, sadly. There are a few that made it to the blog, but I'm not sure which posts they're in.

Anonymous said...

Heh, yep, I've got one of the common A. barbadensis. It offsets like crazy (I separated off ten or so plantlets three months ago, and it's already got more, and I swear you can see them growing). Thanks for the tutorial on how to do it right!

Hermes said...

Really good post. I use Aquatic soil as well.

Karen715 said...

Out of curiosity, what is the composition of the Ball potting mix? I'm asking because I didn't know there were any potting mixes (as opposed to potting soils) commercially available that do not have peat as a major component. At any rate, I'd have to search high and low for any specialty soils not packaged by the major brands. Even the good nurseries around here seem limited in their selection.

So I admit it; I use Miracle Gro. I don't actually endorse it, and I amend the hell out of it, so it is usually between 1/2 to 2/3 of the final mix, depending on the moisture preferences of whatever I'm potting. (As amendments I use bark, perlite and aquatic soil in various ratios for leafy plants, just perlite and aquatic soil for cactus and succulents. I'm not trying to emulate a certain GW poster's "gritty mix", but I did get the ideas for possible amendments from him.) My plants seem happy with the doctored MG.

mr_subjunctive said...


You might actually be fairly close to the Ball mix, then, if we assume that the Miracle Gro is 100% peat (as it appears to be sometimes). The Ball package says it contains:

45-55% composted bark (which is pine bark in the eastern and central regions and fir bark in the west: no definition of exactly where these regions begin and end, of course)
Canadium sphagnum peat moss
dolomitic limestone
"wetting agent"

So it also contains peat moss; it just manages not to act like peat moss. (There's a Ball seed-starter mix that's only 30-40% peat, which does act somewhat like Miracle Gro, though it still rewets better than MG does.)

According to the Miracle Gro (Canada) website, MG contains:
peat moss
compost (which may include animal manure, composted leaves, grass clippings, and/or composted bark)
slow-release fertilizer

The "moisture control" product also contains coconut hull fiber, which they say holds 33% more water than regular potting mix. So it's probably even worse, by itself, for indoor plants, though in fairness, they don't seem to be marketing it toward indoor gardeners so much.

The Miracle Gro product is also not sterilized ("nor do we claim to on the package," they add, somewhat defensively), and they all but tell you to expect fungus gnats. Admittedly, fungus gnats aren't that big of a deal, but from reading the website, you almost get the impression that you're supposed to be grateful for them, as they're just evidence that the soil hasn't been sterilized and contains helpful microorganisms. To which I say, what-ever.

IIRC, you should be more or less in Ball territory already (they're based in Illinois, I believe), so I'm surprised it's not easier to find. Though I probably wouldn't know about it if I hadn't worked in a place that did some of their own transplanting and bought plugs from Ball every year: I haven't seen their potting mix for sale anywhere else.

I also got the idea to amend with the aquatic soil from the GW poster you don't mention; I couldn't find Turface around here, but the aquatic soil appears to be basically the same thing, if a more expensive version thereof.


I neglected to say that yes, the headache is more or less gone, though I get mild headaches a lot. (So do both of my parents; some kind of sinus defect is suspected in both cases but has never been proven.)

mr_subjunctive said...


I'm not inclined to give Ball all my personal information to ask, (seriously, Ball, way to be super-duper invasive: they require name, full address, phone number, company, and occupation just to ask a damn question) but if you're interested in finding some of their soil, you might e-mail them and ask for a list of nearby retailers: there have to be some somewhere near you.


Nature Assassin said...

This was great. I just separated a pup from my aloe parvula "jacobsonii" and now I can see I definitely overwatered. I'm about to separate my Aloe "Dorian Black" pup, so I won't make the same mistake.

So here's a question. I've heard about perlite adding extra fluoride, so when I amend soils, I usually use 1 part perlite and 1 part pumice instead of 2 parts perlite. I can get nice, pebble-sized pumice in big bags for $5 a pop at a local place, so that saves me quite a bit of dough. Now I'm wondering though... could the pumice be unbalancing my Ph? I rinse it well before I use it, but it does give off a fine red dust. Do you think it's safe?

mr_subjunctive said...

Well, googling about pumice pH gave me about the same number of hits for pumice raising pH and pumice buffering pH. I don't know if pumice really has that variable of an effect, or what sort of impact it might have on soil pH for indoor plants, but I would be really surprised if it were actually unsafe.

That said, as far as I've ever heard, fluoride is not that big of a deal for succulent plants: the plants most affected by it are typically tropicals with long, skinny, non-fleshy leaves. So my guess would be that you could probably use either for the Aloe, though if you're unconvinced by my shrugging and mumbling "I dunno" you could skip both and instead use something like the aquatic soil, or aquarium gravel.

Anonymous said...

are you sure that's Black Gem? I've got one of these at home(looks identical) and a black gem and there are clear differences between them. this one however I'm still trying to ID so not sure what it's called yet.

mr_subjunctive said...


Well, that's how it was identified to me when I got it, from an Aloe collector. (I've since learned that Alworthia 'Black Gem' is the more correct name, so it's not like he couldn't have made a mistake. I intend to change this on the blog eventually.)

Not saying it couldn't be something else, but it does turn nearly black in bright light, and I've got no other name for it, so.

Anonymous said...

no worries, the one I have doesn't actually change colour in the sunlight, what I know as black gem looks like this.

this one is the only plant in my garden that I can't ID. it's taken me no time to ID everything else, but this one still eludes me. I think I might need to find out where it was purchased and find out what it is exactly.

Unknown said...

I know I'm a bit late to this party, but mr_subjunctive's plant is definitely ×Alworthia 'Black Gem'. The link provided by Anonymous is now defunct but I suspect that the plant THEY have is a rather mysterious plant known variously as
Gasteria nigricans (OR pseudonigricans) f. monstruosa or Gasteria 'Black Boy'. The problem with the name is that G. nigricans is no longer a recognized species name, and that the 'Black Boy' tag seems to have come out of nowhere just a few years ago, even thought the plant has been growing here and there for decades as I can remember seeing (and coveting) one back in the 1970s. ARRGHHH! The 'Black Boy' plant exists in two versions - a very tight small leaved version which does look a lot like ×Alworthia 'Black Gem' EXCEPT that the leaves are always much darker in colour and stiffer in substance, and the "reverted" version which has much bigger flatter leaves and does at least vaguely resemble a regular Gasteria!

What the "REAL" name of this plant should be is a particular bug-bear of mine as I have owned once since 2007 without actually being able to find a name I'm actually happy with from a botanical standpoint.