Pleiospilos nelii

Many people will have seen a nearly spherical green plant, perhaps mistaking it for a Lithops, possibly not even realising it was a plant at all. Pleiospilos nelii (P. nelii to its friends) is a popular novelty plant and you may even have owned one yourself at some time. Probably almost as many people have killed one and only a lucky few will have seen the spectacular flowers.

Not a Lithops

P. nelii is in the same plant family as the Lithops, sometimes it will even be labelled as a Lithops, but it isn’t the same. There are two immediate visual differences: P. nelii does not grow buried to its neck in the ground; and it is bigger than any Lithops. The round leaves naturally sit above the surface of the soil and can grow to about four inches across. Mostly there will just be one head, but very old plants will form two and eventually more heads.

There are some other differences not so easy to spot. P. nelii usually flowers in spring, although some plants can flower in autumn like a Lithops, depending on how they are grown. Quite commonly a single pair of leaves will produce multiple flowers at once, something that Lithops never do. The flowers themselves are large, orange or orange-yellow, and have a great many petals.

There is actually a whole genus of Pleiospilos plants, mostly with longer thinner leaves than P. nelii, less rock-like but still with the same speckled grey-green appearance.

Growing a Split Rock

For many gardeners, growing P. nelii is not as easy as killing it. It is an extreme succulent plant from a barren hot environment in South Africa. For most people, planting it in the garden is just not an option, it is not frost-hardy, it will rot if it stays wet, and will become mis-shapen and possibly die if it is watered heavily more than a few times per year. For an idea of how succulent these plants are, a mature specimen can easily go a whole year without any water in a typical European or North American climate.

So the first rule is to plant into a soil that drains quickly and doesn’t retain much water. A clay pot may be a good idea in cooler or more humid areas. All Pleiospilos species like to be watered lightly and frequently (frequently compared to a cactus!), rather than a heavy watering followed by many weeks dry.

P. nelii is a very adaptable plant, it will grow whenever it has water and good sunlight, but it will become dormant in very hot weather to conserve water. Like Lithops, it will produce a new pair of leaves from between the old ones during the winter, then the old leaves should be consumed to return to the split rock shape. A plant that retains its old leaves right through the summer is being overwatered, it may not flower and is at risk of rotting and dying. P. nelii loves direct sun and warmth. Always aim for a nice round split rock and never overwater, the recipe for success with this fascinating plant.