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| This living wreath has a mixture of leafy succulents: hens-and-chicks from Europe, Echeverias from South America and Crassulas from Africa. |
One-third of the world’s land area is covered in deserts. As a working rule, deserts are often considered to be places receiving less than 10 inches of rainfall a year. Life amongst the thorns and stones persists, adapts and evolves in these thirsty environs according to the rhythmus of rainfall.
Every desert is unique and different yet somehow alike as plants mold themselves to tolerate long periods without water. One of the most common adaptations is for plants to become succulent - the botanical equivalent of a water-filled sponge.
Succulent plants take on many forms and are found in more than 60 different plant families - everything from succulent members of the African violet family to orchids. A few plant families - the Cactaceae (cacti), Crassulaceae (sedums, jade plant), Aizoaceae (living stones, ice plant), the Euphorbaceae (candelabra cacti), Agavaceae (century plants, yucca), Asphodelaceae (aloes, Gasteria) and a few others - are almost completely composed of succulent plants adapted to desert environments, whereas most plant families have only a few species with succulent characteristics.
Succulence can take many forms but revolves around the idea of water storage during periods of extreme drought. Cacti and euphorbs primarily store water in leafless trunks and branches; the crassulas, ice plants, aloes and agaves store most of their water in swollen leaves. A few develop a subterranean approach and go below ground to escape drought.
Co-evolution is the term used to describe the phenomenon of widely separated plants employing the same strategy for dealing with an environmental challenge. In succulent plants a number of examples can be cited: cacti (from the Americas) and tree form Euphorbias (from Africa) have evolved as leafless hulks armed with thorns; the century plants (Agavae of the Americas) look and behave almost the same as the Aloes of Africa.
Succulents share a number of water-saving features. Their plant bodies tend to be reduced in size with leaves, if they still exist, usually with a high volume in relation to their surface area. These same leaves are usually covered with a waxy coating or a white pubescence that helps reflect sunlight, keeping the inside of the leaf cooler and reduces the need for transpiration. Arming the leaves with sharp tips or an abundance of spines is common amongst many succulents, not just cacti.
Almost all succulents employ crassulacian acid metabolism with the stomata opening during the night when water loss is minimized. Carbon dioxide is taken into the leaves and stored as carbonic acid during the night with photosynthesis proceeding normally during the day.
Succulent plants are a diverse group of species that have always attracted the attention of gardeners. In the perennial garden, we grow sedums and hens-and-chickens, both succulents of the Crassulaceae family and closely related to the frost-tender jade plant found in many of our homes. Other leaf succulents such as Haworthia, Gasteria, Aloe, Agave, Sansevieria and others are unique and interesting tabletop and windowsill specimens.
Succulents do best when a traditional potting soil is combined with an equal volume of sand. This provides good drainage and ballast for the plants. As a rule, leaf succulents require more water than stem succulents such as cacti and the euphorbs. But, during the wintertime when light is low and growth generally stops, reduce watering and allow the soil to dry before watering. Fertilize only during the spring and summer when plants are making active growth.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
February 15, 2008
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