Adeniums are deciduous succulent shrubs with origins in South Africa. Different varieties are popularly called the desert rose, impala lily or sabi star. They are among the most colorful and decorative of all succulents, producing masses of striking crimson, red, pink and white bicolor flowers. Growing adeniums is easier if the conditions of their natural environment and evolution are understood.
Five species of the genus Adenium are recognized. Adeniums have thick, tuberous underground stems that help them to survive long periods of drought. Their leaves, about 4 inches long, are dark on top and light on the bottom. In their natural habitat they are small and shrubby if they are browsed extensively, but grow into trees in protected areas. Plump adeniums often resemble miniature baobabs. Their seeds have silky tufts allowing them to be blown by the wind.
Adeniums do well in temperatures ranging from 85 to 95 degrees F with moderate to high humidity. They will go dormant and lose their leaves when nights regularly drop below 50 degrees F. When they are dormant and dry they can withstand near-freezing temperatures, but a light frost can cause root rot and death. When dry and dormant Adenium swazicum can tolerate temperatures in the upper 20 degrees F.
Grow adeniums in containers if your climate has cool, wet winters or frost. Potting mix should provide good aeration and drainage. Adeniums grown indoors have fewer problems with insects.
Face an adenium in the same direction all summer. This allows different parts of the plant to receive some light and prevents burning on one side. Adeniums grow spindly if they receive sun less than half the day or are grown in a climate with cloudy summers. In desert climates they like light afternoon shade.
Adeniums are apparently forest plants that adapted to arid conditions as climate changes shrunk the forests. Consequently they respond to generous watering during hot weather. Dr. Mark A. Dimmit, Natural History Director for the Arizona-Sonora Desert Museum, says adeniums should be grown as wetland tropical plants when they are growing; they should be treated as desert plants when they are dormant. Dimmit advises gardeners to care for adeniums in hot weather as if they were tomato plants.
Reduce or stop watering an adenium if it shows signs of going dormant or if the nights regularly drop below 50 degrees F. If adeniums are watered too much before dormancy ends, they are susceptible to root rot. In the winter water them sparingly as if they were cacti. Water large, dormant adenium as little as once a month. When the terminal buds begin expanding in the spring, increase watering gradually.
Adeniums that are chronically waterlogged any time of the year may develop root rot.
Adenium leaves turn yellow and begin to drop at the onset of dormancy. A. boehmianum and A. multiflorum lose all their leaves. A. arabicum and A. somalense retain their leaves if they are watered sparingly. A. multiflorum and A. somalense flower primarily during their dormant periods.
Adenium seeds will germinate in about one week at 85 degrees F. Seedlings will grow during the first winter and go dormant the second winter. Dip tip cuttings in root hormone and plant in a well-watered, coarse growing medium.
Adenium respond well to regular and generous fertilizing. Add slow-release fertilizer and micronutrients to potting mediums. Inadequate watering and feeding are the primary causes for slow growth in adeniums.