About the genus
The genus Gibbaeum was established by Dr N E Brown in 1921 The following year he gave a more complete description of the genus, partly drawing on Haworth’s writings and partly from examining living plant material.
Gibbaeums are dwarf succulents which form clumps or tufts capable of reaching up to 20cm tall. Stems, where present, are short and upright or can grow horizontally. Although some roots can be fleshy, the plants will more likely develop short, stout, woody rootstocks with age.
The leaves are very variable in colouration ranging from; light to dark green, bluish green, whitish green, reddish, metallic grey or grey white. They can be entirely smooth or glabrous, or may have a velvety appearance due to the minute hairs which are only visible with a magnifying glass. Flowers are borne on stalks, are variable in size and come in various shades of pink to dark purple or white. The quartz fields of the Little Karoo of the Western Cape Province are the favoured habitats for these plants, and it is common to find two or three different species growing together.
How to grow them
Gibbaeums grow in areas of summer and winter rainfall, mainly March and November in South Africa, where they will receive around 125–250mm per annum (5–10in). Bearing in mind that the seasons are reversed in South Africa this gives a strong indication of the times to water in the greenhouse. Gibbaeums enjoy strong sunlight, something that is not too prevalent in the British climate, so a position close to the greenhouse glass is advised but it should also be one that can be well ventilated to allow a good air flow which will prevent stagnant air that often leads to scorch or rot.
You should be judicious with the amount of water given to the plants as they will very easily split their bodies if overwatered. The bodies will tell you if they are in need of a drink because they start to wrinkle. Just a touch of water will soon return them to a turgid state. Give them a spray in mid-August and start careful watering in September, which will be repeated in October and November, if required. They will then ‘rest’ till March and April, unless they show signs of stress, when a further drink can be supplied to prepare them for their normal rest throughout the warmer summer months. Some shade is advised during a northern hemisphere summer. They will need to be watched carefully because it is important to keep the roots in good condition. You can offer a modicum of water in the ‘non-growing season’ for gibbaeums and indeed most mesembs to preserve the condition of the roots but not enough to cause unwanted growth.
A gritty soil mix is essential and fertilising just once during the growing season is more than enough. Try not to let temperatures go below 4°C but they can take an occasional light frost provided they are completely dry. They are best propagated from seed.
Peter Bint
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