Adenium is a type of flowering plant in the dogbane family, Apocyanaceae. There is either one species, Adenium obesum known as desert rose, or several species in this genus, depending on the views of different botanists. The desert rose is from the African and Arabian deserts and can tolerate high heat, up to 120°F (48.9°C). It is a very distinctive succulent that grows with little water and produces distinctive red, pink, or white flowers. This shrub is grown as a houseplant by collectors, but it can be a difficult plant to grow.
The appearance of an Adenium is quite distinctive. Instead of a trunk, the plants have a swollen base known as a caudex. Thickened stems referred to as pachycaul grow from it. The leaves are clustered at the tips of the stems. Flowers are produced in late winter, in its natural environment, varying in size from 3 to greater than 8 inches (7.5 to 20 cm) wide.
When grown as a garden plant, Adenium usually starts to flower in the spring, even before new leaves are produced. If the summers are really hot, it may stop producing flowers until the fall. Many of the hybrids will bloom all year, if they are kept warm and well lit.
Since Adeniums are succulents, like cacti, they are designed to grow with minimal amounts of water. The plants store water to carry them through dry periods in the desert. When grown by gardeners, it is very important that the plants be grown in a soil mix that drains well, such as a commercial cactus mix. They should be thoroughly watered and then allowed to almost totally dry out before they are watered again. Ideally, they should be kept in clay pots, since these types are less likely to retain excess water.
Temperature is a very important factor in watering the desert rose. If the temperature at night is less than 50°F (10°C), or 80°F (26.7°C) during the day, the plants should not be watered at all. If they receive water under those conditions, they are likely to succumb to root rot. Plants will receive some damage at 40°F (4.4°C), but will recover. Prolonged exposure below this temperature will cause death or serious damage to the plant.
Lighting is also a very important factor for Adenium. During its growing period, from the spring through the fall, the plant needs as much light as possible. Even so, in areas with strong sun, the plants should be grown in filtered sunlight. Mature specimens can be located in full sun, however.
As winter approaches and the temperatures grow cold, the plant will drop its leaves. It should then be brought indoors to a very bright location and kept dry. As spring approaches, the plant should be placed outside. It should be gradually introduced to bright light, so that it does not suffer from sunburn. The plants should not receive water until they start growing or producing flowers. Healthy plants should be fertilized once per month, with half-strength houseplant fertilizer, during the growing season.
Unlike most plants, it may be best to keep the Adenium at the same size — or prevented from growing — if it is at an appropriate size for blooming. If this is desired, watering and fertilizing should be performed infrequently. One should only fertilize every two months while the plants are growing. Plants grown outside can reach proportions unwieldy for houseplants, such as up to 9 ft (2.7 m) tall.
The milky sap of these plants is poisonous if taken internally. Tribesmen in Africa are reported to use it on their arrows for hunting. For this reason, one should take care with this plant if it is grown around children or pets.