Foregoing chapters have made it clear that we can learn something about the cultivation of succulents by reference to their native habitats, notably in the cycles of wet and dry, hot and cold, that determine when the plants grow and when they rest. Although a few (mostly denizens of the humid tropics) can be kept growing all the year round, most respond to an annual rest period, and may fail to flower unless this dormancy is observed by phasing out watering at the onset of winter, when light and temperature are limiting factors to growth. Usually this has the desired effect, and the plants can be lulled to sleep even if the seasons are reversed in relation to their natural home. A few, however, resist attempts to alter their normal annual rhythm of growth and rest: Conophytum, for instance, Gibbaeum (certain species) and some other dwarf Mesembryanthe-maceae. Canary Island aeoniums tend to rest during a northern summer, no matter how freely they are watered, and to grow in late autumn. The best that can be done for such plants is a compromise: put them right up near the glass in the lightest position.and water cautiously for only as long as they indicate by growth and flowering that water is needed.
Many plants are sensitive to day length (photoperiod) and will flower only in response to decreasing or increasing the hours of sunlight. "Short-day plants" react to an increase in the hours of darkness, which can be achieved, for instance, by covering in black polythene. "Long-day plants" respond when the day isextended by means of artificial lighting. Both techniques are used commercially to force flowering out of season. Good examples of short-day plants are Kalan-choe blossfeldiana and the 'Christmas Cactus' (Schlumbergera). Sedum specta-bile and S. telephium are long-day plants'. For Echeveria harmsii to bloom it must have a succession of short days followed by long, whereas Kalanchoe lubiflora. K integra and Aloe bulbillifera need long days followed by short.
Certain succulents are notoriously shy about flowering in captivity, even when mature - Mitrophyllum (11.11), for instance. The natural impulse is to give them extra light. However, success might come from actually shortening the day —that is, by turning lamps on for a limited number of hours each day, followed by total darkness. There is room for some important experiments here.
Right (6. 1): One ot the most celebrated ot many outdoor gardens in southern Europe, this at La Mortoia in Italy was lounded by Thomas Hanbury in 1867 and has always
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