Mesembs! My favorite plant group. I’ll be talking about the humble Pleiospilos nelii in this post, a cute little plant that is the gateway drug into succulents for many people.
Pleiospilos nelii, the split rock plant
The common name for this particular plant is the “Split Rock Plant”, because that is exactly what it looks like: a lumpy little split rock. Depending on who you ask, they also can strongly resemble the feces of the large African mammals that meander through their growing areas. Whatever it is they’re mimicking, it’s effective!
Pleiospilos nelii is just one of the Pleiospilos genus, and is far and away the most common. This is likely due to their forgiving nature in cultivation, as well as how readily they bloom through winter months.
The pleiospilos genus is found primarily in the Little Karoo region of South Africa, where they grow in stony, rocky soil. The leaf colors commonly mimic the stones against which they grow, making them hard to spot in situ. The map indicates the general area of South Africa they can be found, and is by no means a precise location.
Pleiospilos nelii in habitat
The natural environment for Pleiospilos nelii is a typically dry, hot desert with intense light and minimal rainfall. Unlike other pleiospilos, nelii in particular needs winter moisture in order to flower, but not an excessive amount. Average rainfall in their region is 150 – 300 mm, or around 6 – 12″ of rainfall. Contrast that to various areas of the US:
- San Diego – 12″
- San Francisco – 25″
- Seattle – 37″
- Omaha – 31″
- Austin – 34″
- Chicago – 36″
- New York, New York – 45″
- Tampa – 51″
- Washington, DC – 43″
Naturally, here in San Diego, we’re well positioned for comparable amounts of moisture, but we average at the high end of what Pleiospilos will tolerate. Our temperatures are also similar in highs and lows, depending on what part of San Diego you’re in. Little Karoo’s warm season averages in the high 70s, low 60s, with the cold season dropping to high 60s, mid 40s. For my area of San Diego, we drop to the low 30s, and our high temperatures are often in the 100s.
Use this information to help you decide where, and how, you’ll keep your Pleiospilos. If you’re in a colder northern region with heavier rainfall or even snow, your split rock should come indoors for cold or rain. If you’re in a warmer region in the Southwest, you can probably do as I do and keep them outdoors in a partially shaded area pretty much year round. In warm and wet regions (Florida, I’m looking at you), you’ll need to consider how you’ll keep them dry enough but also bright enough. Most rain for this genus occurs in the summer, with rare winter showers. When it’s hot, you can be significantly more generous with water for these than you would in winter. For San Diego and my fellow Southwesterners, that’s our biggest growth challenge – we get the most precipitation during our cold seasons.
The soil these grow in is typically semi-arid shale or sandstone flats with low shrubs and grasses, where large game used to graze. In modern times, it’s usually grazed by sheep.
My first Pleiospilos nelii, picked up in late 2016, blooming in March of 2017
Pleiospilos nelii in cultivation
These are enormously easy to grow if you meet even the barest of their needs. They can survive indoors by a bright window, outdoors in the right climate, or a blend of the two if your summers are ideal but not winters (or vice versa).
They need well draining soil, bright light bordering on bright/indirect, and a sparse amount of water. While they come from the same general region as lithops, these are more forgiving and less strict about their growing cycle. Unlike lithops, which you should sort of gauge water needs based on growing cycle and how wrinkly they look, these you should generally water well once they start to prune from dryness. That usually means the soil is dry to the touch and stays that way for days, even weeks, between watering. Unlike other Pleiospilos in their genus, the neliis do need water in winter if they are to bloom, so they tend to do better for novice or beginner mesemb growers that worry about lack of water through the winter months.
Blending Soil for Pleiospilos nelii
The one thing I will say that you should do for the best success with your Pleiospilos nelii is to mix your soil with perlite or, preferably, pumice. This increases the drainage and aeration of the soil blend, and makes it more of the mineral, rocky mix that they prefer. The increased drainage also means it dries out faster, which goes a long way to preventing root rot.
To make your Super Special™ Pleiospilos soil blend, mix about 50/50 pumice with a quality succulent soil. If you’re using EB Stone, like I have been lately, that tends to be a good mix, although if you can get your hands on the Black Gold cactus mix, you can mix an even higher ratio of pumice in. I’ll usually also add a touch of sand and/or orchid bark for texture, and the bark breaks down slowly over time, providing nice chunky organic material without turning into a dry soil cake. For a 4″ pot, the amount of bark is pretty much just a small sprinkle, mimicking the larger chunks of bark, leaves, or debris that would likely be in the soil if they grew naturally. Make sure to mix thoroughly, then plant your Pleiospilos nestled into the soil, with the outermost leaves touching the top. You can place rocks or more pumice as a top dressing if you’d like, or stage with larger stones.
My original Pleiospilos nelii in February 2019, larger and blooming even more profusely! Here in San Diego, I tend to see my Pleiospilos nelii blooming from late January through early March, sometimes blooming multiple times.
Pleiospilos nelii “Royal Flush” – the purple split rock
Purple split rocks are nearly identical to regular neliis in care, although in my experience, they seem to be slower to grow and smaller in size. Their deep purple color intensifies with more exposure to sunlight, and they can revert to nearly pure green again in shaded conditions. Too much sun will turn the purple into more of a brownish maroon, although that is not a problem you’re likely to have unless you’re further south and have lots of hot, sunny days.
While regular split rocks will typically bloom a nice big orange flower, the royal flush or purple split rocks will produce a brilliant pink flower instead!
Typical Growth Rate
Similar to the other mesembs that resemble stones, Pleiospilos nelii grow by producing two new leaf bodies once they’ve finished blooming for the season. In natural growing conditions, this is typically happening during dry winter months, so the plants slowly absorb their older, outer leaves while the new center leaf bodies emerge. The harsh conditions in the wild contribute to the plants almost always existing as just two leaf bodies per head. When kept “too well”, as in, with plentiful water, soil nutrients or fertilizer, and light, Pleiospilos nelii doesn’t always absorb the outer leaves when producing new ones. Whether this is desirable or a sign of good cultivation is up to the grower; some may take pride in nurturing their Pleiospilos into towers of leaf bodies resembling zebra poo, while others prefer to nurture their plants similarly to their natural environment.
Which way is the right way? It’s your choice. It’s your plant, after all. Just be cautious of the plants with plentiful water, as it can be easy to overdo it and rot out the roots.
My first nelii (from 2016) in November of 2019, showing that it has produced a new head. By this time I’d staged it in a larger pot (which it’s still in now), with quartz to resemble the natural environment it would be in. As I leave it out to experience our winter rains, it’s challenging to limit its water enough for the leaf bodies to be as sparse as they would be in the wild.
Same nelii in February of 2020, beginning to bloom from all heads. You might be able to see the weird mutant third head just barely visible at the back of the plant.
My oldest nelii as of February 2021, after a hard-grown year. It is definitely time to repot it, as the soil no longer gets thoroughly wet all the way through. It tends to only get a truly thorough watering when we get rain, which has mean 2020 was a relatively hard year for it. It’s gearing up to bloom, though, so it’s not too miserable. I’ll likely stage it and hope that we’ll be able to have cactus and succulent shows again by later this year.
My 2019 “Royal Flush” as of February 2021, showing the slow stacking that happens when the plant isn’t grown harshly enough to properly absorb older leaves. This plant could also use a repot, as after watering, it’s clear that the soil didn’t get wet all the way through. You can see that the outer leaves are more of a brown-green than purple, which is due to both the age of those outer leaves as well as over exposure to sunlight. Only the newest leaves tend to have the bright purple color, and for the best coloration, the plant should be kept with morning sun and afternoon shade. I’m not sure I’ll get a bloom from this one this year, which is ironic considering it hasn’t felt the need to absorb outer leaves for while.
This is one of the pleiospilos nelii I planted in-ground as an experiment, along with some lithops and other mesembs. Our average annual rainfall is so close to what these get in the wild, and we have this perfect slope of rocky quartz, that I figured I’d give this a try. I always end up with a handful of plants that end up scarred for some reason or another, and I chose to learn from them rather than count them as a loss.
I placed these in-ground in September or October of 2020, and the photo above is the plant splitting in November.
Same Pleiospilos, this time in late January 2021, right before we got the hail storm. You can see that the new leaf bodies have dwarfed the old ones, and it’s preparing to bloom. It’s produced three bloom stalks, although only two are left, as something keeps taking chomps out of my in-ground mesembs (a definite draw back to the in-ground method). Even with nearly an inch and a half of rain over the space of one weekend, plus hail, the rocky quartz and clay/soil mix has dried out rapidly, keeping the roots dry enough when the weather has been cold.
Pleiospilos nelii are slow growing, charming little turds that should be a low-stress introduction to mesemb growing. They can be combined in arrangements with similarly low-water needing plants, but are likely to do best with other mesembs of the slightly thirsty variety, such as aloinopsis or titanopsis, due to the similar soil and moisture requirements. There are few new world succulents that are likely to share the same growth cycle and requirements, but you could look for a suitable euphorbia or potentially aloe to pair in an arrangement with your pleiospilos.
Honestly, the mixed pot is hard when it’s a plant with specific needs like this! I personally wouldn’t plan on having these in an arrangement long term, but they can look cute if you’re only planning on having them sharing soil for a short time.
To see updates on my in-ground experiment, or on my 5 year old turd, follow me on Instagram – @TrexPlants!