Adenium obesum, also known as Desert Rose, is a unique looking plant used for both indoor and outdoor gardens. Several species and sub-species exist, with new hybrids continually being developed. Adenium is grown in large commercial operations in tropical areas, especially in Asia. The plant's form can be "designed" through grafting and pruning so that it grows as a small houseplant or as a shrub or tree. It is a perennial, and it will survive mild winters as a deciduous plant where temperatures are cool but do not dip below freezing. Even indoors, adenium plants may be semi-deciduous as they go through a period of dormancy.
Adenium obesum is native to Aden, now known as Yemen. An expedition from Denmark in the 1760s made the first classification of the interesting plant. The natural range of adenium extends through India and tropical areas to northern Africa, where the toxic sap was used to kill fish and for poison arrows. Adenium is toxic to livestock.
Thailand is home to huge commercial operations that supply plant markets all over Asia. Commercial growers export seedlings and cuttings as well as mature plants. Here the art of grafting adenium has been perfected. Plants are grown from cuttings and seeds for use in grafting. Adenium is very popular as a specialty plant in the bonsai market worldwide. Bonsai adenium develops interesting trunk formations, while the leafy branches can be pruned and trained to maintain the miniature form.
Adeniums are extremely popular in China, where they are a good luck plant. Red is a color of good luck, and red adeniums are popular gifts for weddings and other occasions.
Adenium culture is rather specialized in the US due to the climate it requires. The mainstream houseplant market in the US is increasing for this unusual plant.
Adenium has a caudex, or non-woody trunk. The caudex swells into an ovate shape, and the leaves are arranged in spirals on the branches that grow from the top of the caudex. The branches grow in a spreading, umbrella-like fashion from the central point. Blossoms develop along the branches. The flowers are various shades of red and pink, usually with white areas at the center. Some species are grown for the caudex characteristics, and others are grown for their specific flower characteristics. The selected flowering tops are grafted onto selected caudices to tailor plants with desired form and bloom.
Basic care requirements are the same for seedlings as well as larger plants. Adenium has a reputation for being difficult to grow. The plants are often mistakenly treated as a desert succulent and are watered sparingly year round. However, adenium is a tropical plant that requires plenty of water and fertilizer during the growing season. The soil should never be soggy; good drainage is very important. Only when the plants are dormant should water be reduced.
Adenium responds to high nitrogen fertilizer during all phases of growth. Seedlings grow very quickly under warm, humid, tropical conditions. They can be topped by clipping the growing tips to encourage branching. Potted adeniums must have plenty of room for rapid growth in the spring and summer. Rootbound plants will have very slow growth at any stage. Seedlings need to be repotted regularly for optimum growth.
Light should be bright, and full sun is recommended. Adeniums kept in a window or in a container garden do not need to be rotated to achieve even lighting. Foliage that is acclimated to the shady side is easily sunburned and damaged if it is suddenly turned to face bright sunlight. Foliage will quickly regrow if it is lost due to sunburn. Make changes in light exposure gradually to avoid sunburn problems.
Pests and Diseases
Damping off is a fungal disease that causes rot at the soil level on seedlings and rooted cuttings of adenium. When it occurs in commercial hothouses, growers often simply remove affected plants to avoid the spread of the fungus without using chemical treatments.
A small oleander moth caterpillar eats the leaves of young adenium plants, and growers usually hand pick them. The poisonous sap is potent enough that insect pests are not normally a problem.