Adenium covers a small genus of flowering plants that belong to the family Apocynaceae. The most popular and commercially distributed species of Adenium is the Desert Rose (Adenium obesum). Adeniums are native to parts of the Arabian Peninsula (mostly Yemen, Oman and Saudi Arabia) and sub-Saharan Africa. Etymologically, the word Adenium is linked to the word Adean, an old name of a region of Yemen where, in 1762, the German botanist Pehr Forsskal discovered the plant. The common name of the popular species Desert Rose comes from the fact that the plant thrives in the sub-Saharan regions. The epithet obesum means swollen, and is a reference to the chubby stem base of the plant. Adenium plants are also known under several other common names, including Adeno, Sabi star and Kudu.
The plant has a uniquely shaped, chubby or bulky caudex (trunk) which stores water, making Adeniums drought-tolerant and resilient. The leaves are green, space and spirally distributed. The Desert Rose flowers are tubular, typically pink, red or white, and have a diameter of approximately 5 cm. Some hybrids have yellow, white, purple or black-edged flowers. In their natural habitat, some Adenium varieties can grow over 3 meters tall. Adenium socotranum, known as the Aden Rose of the Island of Socotra, is a giant tree whose trunk diameter is over 2 meters, and height over 4.5 meters.
The sap from the Adenium plant is toxic to many animals, including cats and dogs. On the island of Socotra, Adenium trees are the only native vegetation that have remained safe from goat menace. However, one exception are the African Impala antelopes, who are known to nibble the branches of the Adenium obesum var. multiflorum tree. This Adenium species is known under the common name Impala Lily. Wild Adeniums are classified as endangered, and are legally protected in several African countries, including Botswana, Zimbabwe, Namibia.
Adenium is an ideal plant to be considered for bonsai. The stunning, massive and swollen caudex with its twisting roots above the soil, make the plant a visual treat. Adeniums, especially when grown as bonsai trees, are often compared to dwarf baobab trees. Across South and Southeast Asia, the Desert Rose plant, especially the one with larger trunk, is a strong cultural symbol of abundance, prosperity and good fortune. As a result, they are highly demanded and prized. The fact that Adeniums are flowering trees, makes them all the more popular choice for bonsai.
This guide provides the foundations of Adenium, especially Adenium obesum (Desert Rose) bonsai tree care.
How Long Does It Take To Grow Adenium, Especially Adenium Obesum (Desert Rose) Bonsai?
In as little as five years, an experienced bonsai enthusiast can grow a fully-developed Adenium tree from a small sapling. While the roots and the base stem are eye-catching, it is important to note that the branch structure is not much ramified. To cultivate an impressive specimen, it is recommended to start from an already established Adenium bonsai tree, acquired from a reputed plant nursery. Growing Adenium bonsai from a seed or a very small sapling requires much more luck, hard work and attention to detail.
How to Plant and Grow Adenium, Especially Adenium Obesum (Desert Rose) Bonsai?
Although challenging, it is possible to grow a Desert Rose bonsai from seed, especially from fresh ones. The seeds should be placed in a well-drained medium such as a mixture of sand and soil. The seeds should be only lightly covered with soil, and watered every three days. Once the seeds germinate — typically after a week or ten days — the seedlings should be kept at a temperature higher than 27 degrees celsius.
Alternatively, the cultivation can start from cuttings. This method is easier, and much more likely to succeed. The cutting should be taken from the tip of a mature and healthy Adenium plant. The cutting should be 10 to 12 cm long. It should be left to dry out first in a shady place, and after a few days it should be dipped in water and rooting hormone powder. After being treated this way, the cutting can be planted and watered daily. The roots are expected to grow in approximately two weeks.
In large nurseries, a very popular method of Adenium bonsai propagation is grafting.
Position, Lighting and Temperature Requirements
Adenium is native to tropical regions. In such a climate, Adenium bonsai can be kept outdoors throughout the year. When cultivated in cooler climate conditions, the plant can be kept outdoors between the onsets of the spring and fall seasons, and indoors during the winter.
Adenium thrives well in sunny settings, with a lot of bright light and moderate shade. When grown indoors, it requires sufficient light and, preferably, south-facing windowsill location. To keep the plant safe, it should be never exposed to temperatures below 5 degrees Celsius. Adeniums are best suited to climates where the temperature does not drop below 20 degrees Celsius. They are quite tolerant to temperatures that go as high as 40 degrees Celsius.
Soil and Watering Needs
The Desert Rose bonsai requires special bonsai soil, made of sand and clay particles, and mixed with organic matter. Such a medium is well-draining, and provides the plant with all the necessary nutrients.
Adenium bonsai also requires regular watering. The plant should soak for approximately 30 minutes, and then be given a period of 7 to 10 days to dry, before being watered again. If the plant is placed outdoors, especially during the hot summer months, the soul should be checked regularly. If it is totally dry, the plant should be watered slowly but sufficiently.
To secure ideal growth conditions for the plant, the humidity level should be moderate. One way to achieve this is by placing the plant on a pebble tray when kept indoors. Avoid excess water, as it can lead to root rot. In winter, if the plant enters its dormant period, watering should be reduced.
The Desert Rose bonsai needs general-purpose liquid fertilizer or one specially formulated for bonsai trees, every alternate month. During the winter, no fertilizer is required, unless the plant is developing new shoots. The fertilizer should be either slow release, or diluted (mixed at half strength). Some experts also recommend the use of bone meal, which provides phosphorus to the plant. Adding fertilizer to the soil is particularly useful in spring, right after the plant wakes up from its dormant period.
How to Care for Your Adenium, Especially Adenium Obesum (Desert Rose) Bonsai?
Essentially, rowing Adenium bonsai does not require too much effort or special conditions. Primarily, the plant needs plenty of sun and light. It needs enough warmth, and protection from extreme cold. Moderate but regular watering and use of appropriate fertilizer are also required.
However, to create an intricately shaped and healthy Adenium bonsai tree, it is necessary to adopt the right approach to pruning, wiring, repotting and pest control.
Pruning and Wiring
Pruning is not limited to any particular time of the year. Pruning of an Adenium bonsai is best done before the plant blooms. Since flowers typically appear on new shoots, proper pruning increases ramification and, consequently, boosts the development of more buds. Any damaged branches should be cut off, and cuts should be made above the leaf nodes.
When it comes to wiring, special care should be taken that the branches are not wired too tightly. If the branches do not get enough space to grow thick, the wiring can leave on them permanent, disfiguring scars. It is recommended to use copper or aluminum wire, as they are soft and gentle on the plant.
Whether pruning or wiring an Adenium bonsai, one should wear gloves and goggles in order to protect the skin and the eyes from the plant’s toxic sap.
Repotting of an Adenium bonsai should be done during spring, every two to three years. The width of the new pot should not be less that two-thirds of the height of the bonsai plant. Before the plant is transplanted, the old soil around the roots should gently be removed, using a chopstick. Up to a quarter of the root mass should be evenly removed, both from the bottom and the sides. All thick and old roots can should be trimmed.
It is recommended that the pot or tray is shallow, since this would lead to an exposure of a larger part of the caudex, without limiting its spread. The pot should have one large and smaller drainage holes. Placing sand, stones or moss on the soil’s surface is an excellent way to ensure moisture retention.
Pests and Diseases
The Desert Rose bonsai can suffer from some common houseplant pests, such as aphids, spider mites (tetranychus urticae) and mealybugs. Infested plants can be successfully treated using a neem oil insecticide, or by wiping the insects away using cotton balls soaked in rubbing alcohol. Caterpillars should be removed, and the bonsai should be sprayed with Bacillus thuringiensis.
The Adenium bonsai should be debugged before bringing it inside for the winter. Appearance of small spots on the stem, or yellowing of the leaves is a sign of over-watering. In such a case, all watering should stop until the soil dries out.
It is important to remember that, at all times, the Adenium bonsai needs to be well taken care of in terms of light, temperature, watering and feeding. Such a plant grows more resilient to attacks from pests and diseases.