About the genus
Lithops are members of the family Aizoaceae (sometimes known as mesembs) which come from South Africa and Namibia, inhabiting an area from south-east of the Tankwa Karoo up to northern Namibia. The word Lithops is derived from the Greek and means ‘stone face’. The plants are also informally known as Living Stones or Pebble Plants.
The individual plant consists of two thickened leaves almost completely fused together arising more or less directly from the root. Each leaf pair is referred to as a ‘body’ or a ‘head’ and most species will gradually offset to produce a clump of several bodies. The leaf top is usually flattened or slightly convex with intricate markings which are of significance in their classification. New leaf pairs grow each year but the basic pattern on the leaf surface remains the same. The colour and markings of the body tend to mimic that of their surrounding habitat leading to very successful camouflage.
Flowers can be expected from most species between July and October. The earliest to flower is generally L. pseudotruncatella and its varieties, and the latest to flower is L. optica ‘Rubra’ which can be in flower at Christmas. Flowers emerge between the two leaves and are usually yellow or white, and sweetly scented.
How to grow them
Lithops are best suited to greenhouse culture but a sunny windowsill can produce surprisingly good results. They should be given good light together with plenty of ventilation to prevent burning.
An important factor when growing Lithops is to prevent bloating or ‘stacking’ of the bodies (when the previous year’s growth has not been allowed to dry out). In general, watering of Lithops should not begin until early to late May, after the previous year’s body has completely dried up and the new bodies have emerged. The plants can then receive a good soaking but do not allow them to stand in water for a long period of time. Over-watered Lithops will become tall, bloated and ugly. Allow the soil almost to dry out before watering again. Lithops are more tolerant of drier conditions than wet!
By the middle of October watering should cease and the plants kept completely dry (with the exception of L. optica ‘Rubra’ which may need a little water up to December). During the dry period each body grows a new pair of leaves, absorbing the water from the old leaves until the new body emerges in April/May when watering can begin once again.
Lithops require a loam-based compost such as John Innes 2 or 3 with about an equal amount of grit for good drainage. Single-headed plants can be grown in 2–3in (5-8cm) pots but their root systems can be quite extensive and many will benefit from deeper pots as they clump up. Fertiliser is not generally necessary for this group of plants as too much will lead to bloated plants. If, however, plants have not been repotted for a long time an extra diluted feed can be applied once or twice during the growing season.
In recent years the most troublesome pest is western flower thrips. This can cause unsightly markings on the leaf surface by attacking the soft new growth of the developing heads. It is difficult to eradicate
entirely but several of the readily available diluted insecticides will give some control. The other major pest is the ubiquitous mealy bug!
Text and photos: Alice Vanden Bon.
No part of this article may be reproduced without permission. Copyright BCSS and the Author 2020