You know how sometimes you get a plant that never seems to do any more than just barely stay alive from one week to the next? I had a Crassula rupestris2 that was like that, from June 2007 until November 2009.
It's not that it didn't grow. It did. But branches also kept drying up. I'd snap them off and throw them away, and then a couple weeks later, there'd be more dead branches. The plant seemed to be able to produce enough new growth to break even, but still: it was annoying, and messy. Finally, one day in November 2009, something amazing happened: I tugged on one dead branch to snap it off, and the entire plant lifted up out of the soil cleanly, like a toothpick out of a cake. No roots at all. Checked the other plants in the same pot, and they didn't have roots either.
Now, I'd gotten it originally as unrooted cuttings, and hadn't messed with it much after sticking them in the pot, other than to water every couple weeks or so. It seemed to be okay with me not paying it a lot of attention. I mean, new leaves were forming. It was getting taller. So I thought we were fine, and it was just not a terribly impressive or interesting plant.
When I found out that these cuttings survived for two and a half years without ever even getting roots, it became much more impressive and interesting, in the way that you'd find your next-door neighbor more impressive and interesting if you discovered that s/he was missing all his/r internal organs or wanted to eat your brains or something. By which I mean that it kind of creeps me out. Plants are different enough from people that "undead" doesn't exactly apply here -- it can still be alive without roots -- but even so, alive without roots for more than two years is a pretty extreme situation, even by plant standards.
Upon making the discovery, I threw the plants away. My logic in the heat of the moment was that if they hadn't grown roots after two years, clearly they were never going to do so, and I needed the space for other, more appreciative, plants. The space part was true, but the rooting part probably wasn't. Maybe something could still have been worked out.
But I doubt it.
This is sort of the way it goes with all my "stacked" Crassulas, like C. rupestris and C. muscosa.3 I really like the look of C. muscosa,4 and have bought it repeatedly, but basically the same thing happens with muscosa that happens with rupestris: a long, slow decline that eventually ends with the stems dying, one by one, from the soil level upwards. Sometimes it happens quickly, sometimes slowly, but inevitably, the plant dies. Some of this may be the fault of the sellers: I bought one muscosa that probably shouldn't have been sold until it was quite a bit better established, because it didn't have much for roots.
In any case, I'm probably not the person you want to be looking to for specific, helpful growing advice. Even when my plants survive for a long time, they're not in particularly good shape. Unfortunately, you don't have a lot of other options. I've googled. Lots and lots of sites, but most appear to have copied from the same original source or from one another, and the instructions are mainly for outdoor growing. This is the best I could come up with:
LIGHT: Outdoors, a lot of people say that direct sun all day long is too intense for C. muscosa, and it benefits from a bit of bright shade.
C. rupestris can handle more light outdoors. In very bright light, it will turn yellowish with red leaf edges, reverting to green if the light intensity diminishes.
Indoors, you probably want as much light as you can get, for either plant. When we lived in the apartment, I kept both in an unobstructed south window, and that appeared to be fine, though they both still stretched a little. You might want to consider growing your plants under bright artificial lights, if you don't have reliable sun or an unobstructed south window.5
WATER: Everybody contradicts one another on watering these plants. A few people even manage to contradict themselves in the same sentence (e.g. "Water sparingly or abundantly."). So I don't know. There does seem to be consensus that you should cut the water way back in the winter, if the plant's going to be at all cold (below 60F/16C). This doesn't explain my plants, though: I don't think any of them ever went below 60F. One of them actually fell apart in the summer, when I know it was never below 70F/21C.
I tried to water mine as I would for a jade plant (Crassula ovata): let it get almost completely dry, then drench; use a gritty, quick-draining soil; and water less in the winter. That doesn't appear to be quite right, but I don't know what I did wrong, exactly. Both species are from Southern Africa, so I suppose if you're in doubt, err on the dry side.
TEMPERATURE: C. muscosa is said to be able to survive temperatures down to freezing, but that only applies if they're dry. Plants that get chilled while in wet soil are likely to rot.
C. rupestris, in its native habitat, is supposed to be able to go even lower, to 25F/-4C, but I would assume that the same applies, that this is only doable if the plant is dry.
In neither case would I recommend that you actually let your plant freeze just to see how low it can go. If you're growing your plant indoors, then I hope finding out how close your plant can get to freezing without damage is hypothetical anyway.
HUMIDITY: Usually dry air is best, though see PROPAGATION below.
PESTS: I've personally had mealybugs on C. muscosa before; C. rupestris never had any bugs while in my care, but I would assume mealybugs would be the main problem there as well.
PROPAGATION: This may be where I went wrong with my C. rupestris cuttings: both species do best if propagated from pieces of stem that have been allowed to callus for a week (give or take), then stuck into coarse sand or some other very fast-draining mix, with good air circulation, bright light but no direct sun, and -- against all succulent-plant logic I'm familiar with -- misted a few times a day. Rooting is slow, and may take up to three months. Once the plant begins to produce new growth above ground, and doesn't pull out of the soil, you can move it to a spot with some sun.
I have successfully rooted C. muscosa before, both at home and at work, but I didn't have a particularly high success rate. I didn't do anything like the above instructions, though: I just cut (or pulled) a piece off and stuck it in dirt, which I watered occasionally. Better luck at work than at home, probably because of the higher humidity and bright, diffuse light in the greenhouse.
GROOMING: I don't really have any grooming stuff for C. rupestris at all. Mine never actually did anything except lose branches.
C. muscosa has bloomed for me, which isn't exactly a grooming issue, but it deserves mention somewhere. I found the smell of the flowers somewhat unpleasant. This was actually PATSP's very first random plant event, and in that post, I initially described the smell as being like a private bathroom someone has just used, then sprayed a heavy, floral aerosol air-freshener around in. Later, I amended that to "a kind of musky, guy-put-on-cologne-six-hours-ago smell." I don't know whether the actual fragrance changes over time, or my perception of it changed as I got more accustomed to the smell. Either way, though. Strong, and borderline unpleasant. It only happened the once, though.
C. muscosa will also trail as it grows; the stems never get much taller than maybe four or five inches (10-13 cm). This is only worth noting because plants are usually sold as small, upright cuttings: if you expect your plant to maintain its upright habit, you're going to be disappointed very quickly.6 Pinching the tips might help induce more branching. I've never tried pinching personally, but Proven Winners suggests it, and pinching usually works with Crassulas.
FEEDING: For both plants, feed lightly (half-strength or a quarter-strength) with every watering, except during the winter.
I've seen variegated versions of both plants. C. muscosa leaves are too small for the variegation to be particularly noticeable, and the plant just winds up looking like a lighter version of the species. Variegated C. rupestris, on the other hand, are kinda pretty, especially if they're getting red margins from being in bright light. (You have to get close to see it, but it's pretty.) There are a few varieties of C. rupestris with different-shaped or -sized leaves, as well, plus a decent number of hybrids with other Crassula species. Some of these can be seen at the davesgarden.com link from footnote 3.
I don't like C. rupestris nearly well enough to try it again. I don't think I'd even asked for it in the first place. So no big loss there. I like C. muscosa quite a bit better, apparently, since I've tried it, on purpose, three times, but I don't think I like it four times' worth. There are too many possible good houseplants to keep failing with the same one over and over. At the same time, though, if somebody's got C. muscosa all figured out and wants to let me know what I'm missing, well, I'd be an attentive listener.
Photo credits: all my own.
Plantzafrica.com (C. rupestris)
Houseplantz.net (C. muscosa)
Plantcare.com (C. muscosa)
Desert-tropicals.com (C. muscosa)
San Marcos Growers (C. muscosa)
Davesgarden.com (C. muscosa)
Davesgarden.com (C. rupestris)
1 I consider C. rupestris slightly easier (3.9) than C. muscosa (4.2), but it screws up the formatting if I try to put more than one difficulty ranking at the top of a post, plus the numbers are only very rough guides in the first place, so that's an average.
2 There's some uncertainty about whether this is C. rupestris, C. perforata, or something else. I sort of had to pick something for purposes of the post, and I found more photos of C. rupestris that matched my plant than I did of C. perforata, so that's what I decided it was. I wouldn't be heartbroken or anything if it turned out to be perforata, though.
3 Those two are the only ones I've tried, but there are a number of Crassulas with this general "stacks of leaves" look. Pictures of several such plants can be found at this davesgarden.com post by Palmbob.
4 Sometimes C. lycopodioides; I've seen conflicting opinions about whether lycopodioides is its own, separate species or just an obsolete synonym for C. muscosa. Davesgarden.com says synonym; I actually can't understand what Tropicos.org says but my guess is that they're saying synonym; and GRIN says synonym, so I think I'm on fairly solid ground to call C. lycopodioides and C. muscosa the same plant. In a retail context, you may see either name being used, though, so it's good to know both.
5 Sometimes this is necessary. I've had a few succulents that just weren't happy with me, even when I gave them a really good spot in a really good window, and didn't shape up until they were sitting a couple inches under a pair of shop lights. Sedum x rubrotinctum is one of those: I've had it forever, and it's always looked miserable in the window, but it's doing really well now under lights in the basement.
6 So of course one of the names the plant is being sold under is "princess pine," which to my mind implies an upright, conical plant with needles for leaves, not a trailing, snaky one with leaves so small they're barely visible. [shrug] I didn't name it that.
"Watch chain Crassula" is a much better name; the pattern of leaves does sort of resemble a small, thin chain.