Mesembryanthemums, or mesembs as they are often known, belong to the Family Aizoaceae and come mainly from South Africa and Namibia. They occur in both summer and winter rainfall areas and this affects their cultivation needs. The majority are small perennials, sometimes shrubby with very fleshy leaves and daisy-like flowers; others are annuals and easily grown from seed. The Livingstone daisy, frequently grown for bedding in the UK, is an example of an annual mesemb.
Mesembs require a loam-based compost with the addition of extra drainage material such as horticultural grit or perlite. They all like good light conditions and plenty of ventilation.
Some are relatively cold-hardy and can even survive mild winters outside. Most will survive temperatures down to freezing point. There are some mesembs which begin to grow in the UK in the autumn as the temperature drops and the days get shorter. Examples are Conophytum, Monilaria and Mitrophyllum.
Because different genera within the mesemb family have different growing conditions, care must be taken with watering. Some genera will benefit from a light spray with water to prevent shrivelling during their dormant period. A table of different genera and their growing times can be found below.
The name Lithops comes from the Greek meaning ‘stone face’ and the plants are often referred to as ‘living stones’ or ‘pebble plants’. There is frequently confusion about the name; it is not a plural word but the botanical name for the genus, and is used to refer to a single plant as well as a group.
Each plant consists of two thickened leaves partially fused together, the surfaces of which are covered in patterns, often in vivid and distinctive colours, which are of significance in their classification (Figs. 1–4). Each leaf pair is referred to as a ‘body’, most species eventually branching with age to form a clump of several bodies. New leaf pairs grow each year but the basic markings remain the same.
Winter treatment: During the winter, Lithops plants should be kept completely dry and not allowed to go below freezing. Even if shrivelling occurs, no water should be given from about mid-November. It may even be necessary to stop watering earlier if conditions are cold and dull, although some species, eg Lithops optica may not yet have flowered, and could benefit from light watering even up to Christmas depending on the sun and temperature. During this period, each body grows a new pair of leaves, the old pair slowly shrivelling up as the stored water is used for growing the new pair.
dried-up skins of the previous year’s bodies
Summer treatment: The main growing period is from about May to October, when the new bodies emerge through the dry skins of the previous year’s growth. Water should not be given until the old skins have almost completely dried up, probably sometime during May or June. As with cacti, the best method of watering is to soak the pot thoroughly and then leave it until dry and then repeat. Do not allow these plants to stand in water for long periods. Excess water should be allowed to drain through and then be discarded, as lithops do not like ‘wet feet’. Whilst fairly tolerant of neglect, they will succumb to rot if over-watered. If in doubt, always err on the side of dryness as over-watered plants grow tall, bloated and ugly. Lithops need very good light at all times and, if kept indoors, a sunny windowsill is essential. Ideally they are best suited to greenhouse cultivation and flowers, usually yellow or white, can then be expected every year between July and October, depending on the species. The flower emerges from between the two leaves at the fissure and is often sweetly almond-scented (Fig. 6).
Occasionally new bodies can become distorted in shape producing extra lobes or even becoming monstrose. Usually this condition will last only for a season and the plant will revert to normal. Sometimes the abnormality can last longer and continue into the next year or even for several years (Fig. 7).
Plants can be obtained from specialist nurseries, florists, supermarkets and garden centres. From these sources, the range may be limited, but they usually offer easy-to-grow species. Preferably though, head for a cactus nursery (see CactusWorld or here for further details), or your local BCSS Branch or cactus & succulent show where you can pick up special and well grown plants plus a wealth of information. Many cacti are also easy to raise from seed, and the Seed Raising page gives details of how to do this and where to obtain seeds.
A full set of cultivation leaflets are given free to new members and are available for sale in our shop.
Images: Andy Young (1, 2, 9, 11, 12, 13(a,b c-f) ) and Alice Vanden Bon (3, 4, 5, 6, 7, 8, 10, 13b)