Jerome Kellerhals’ bonsai garden is in sunny Florida, where he mainly works on semi-tropicals. The Ademium, or desert rose, is one of his favourites and, surprisingly, has much to offer as material for bonsai.
I am going to talk about the styling and caring of Adenium. It contains about 12 species (or, according to a late-20th-century classification by Plazier, only six species). Adenium is the scientific name for the desert rose, which is its common name. Adeniums are succulents and not accepted or regarded as bonsai in some parts of the world such as Japan, Europe, and the United States. Many exhibitions don’t even allow desert roses to be displayed at a bonsai show. I think that is such a shame, because it takes an immense amount of skill to turn a desert rose into a quality bonsai.
In Thailand, China and other tropical Asian countries they produce the best top quality desert rose bonsai, although most showpiece Adeniums are now being imported from Thailand. All the desert roses shown in this article belong to my personal collection and are on permanent display.
Adenium obesum, just like the Arabicum, is widely used for bonsai. Some of its sub species are Socotranum, from the Island of Socotra, and Somalense from Eastern Africa. The Socotranum is my personal favourite species of Adenium, as it grows fast and develops a thick trunk. Its leaves and flowers are naturally small, which make it ideal for bonsai. In spring the flowers emerge before the leaves.
The Obesum leaves can be small or large, and the growth can be bushy or compact. The caudex can be short and fat, or tall and narrow. The flower colours range from white to pink to deep, almost black red. The Adenium Obesum originates from Senegal to Somalia and is also seen on the Arabian Peninsula.
When working on a desert rose, one should know that the branches have a lot of sap flowing when the plant is actively growing. The plant should be allowed to dry out a bit to slow the sap flow before or after trimming to prevent branch rot. The branches are extremely pliable when the plant is allowed to dry. Grafting can be done successfully in the spring.
There are a couple of different ways that you can develop a root system on desert rose, including root exposed, caudex exposed, or lateral root system. Both root exposed and lateral root systems start out the same way, by cutting the caudex in half. Make sure you cut the caudex only when it has your desired thickness, as cutting it slows down the thickening immensely.
If you are creating an exposed caudex, you can expose more of it each year when you pot up your desert rose.
Understanding the language of the leaves
Trying to grasp the language of the leaves on a desert rose can be very challenging because they like to play tricks on us! Sometimes the leaves are yellow and it isn’t clear whether that’s due to too much watering, not enough watering, too cold, too hot, or could it be white flies?
If yellow leaves are present on your desert rose, assess the situation. If there are only a few leaves that have turned yellow, don’t be alarmed. If, however, if it is around three-quarters of the leaves something needs to be adjusted at once.
If it is the middle of the summer, you are in a tropical climate, you have a spot where sunburn is likely and yellow leaves, your desert rose is likely root bound and can’t absorb the water properly. It is, therefore, a good idea to repot it and move it into the shade.
Check the soil; if your succulent is moist and isn’t root bound it could be white flies. Check the underside of the leaves – that is where they are hiding. White flies look like white dust or powder. It is much easier to determine if the desert rose has had too much water; the yellow leaves will have black spots on them, which most likely indicates leaf rot.
If the desert rose is on the drier side in spring and summer it will have yellow leaves due to insufficient water. Always make sure that you assess the situation and determine what the cause is and then remove the yellow leaves and apply your cure. The plant will spend too much energy trying to save those yellow leaves. It is, therefore, a smart choice to remove them and help to redirect the energy.
ADEMIUM – STYLES
Propagate: A desert rose can be propagated from seed or cuttings, but a cutting will never develop a large caudex, which is okay if you are planning on using it as a root exposed or a lateral root spread. Propagating a desert rose from seed is fairly easy and the seeds are readily available.
Repotting: First of all, Boehimanum, Multiforum, and Obesum varieties, are poisonous and contain cardiac glycosides that can cause heart failure. To protect yourself, use gloves when handling all Adenium.
Repotting is most successfully done in the hottest time of the year. In Florida we repot them from June to August. Let the succulent dry out in the shade for a week or two before repotting. The leaves will begin to turn yellow due to a lack of water and will fall off. I carefully use a root sickle or water spray to loosen the plant from the pot to ensure the roots are not harmed.
Adeniums should be bare rooted (washing off all the old nursery soil) when transferred from black soil. Sharp disinfected scissors should be used to trim the roots. After working on roots, the plant should be allowed to dry with its roots exposed and in the shade for one to two weeks to allow the fresh cut roots to dry up. If potted with wet roots, they will rot. Once the roots are completely dried, the plant can be potted. Allow for another week to pass before you water for the first time. Coarse soil, such as pumice, lava rock, calcined clay, and pine bark works best. Once another week has passed, the desert rose can be placed into full sun and watered for the first time. When repotting an Adenium, it should be defoliated, trimmed, and wired all at once.
Watering: Watering the desert rose correctly is essential in developing a very strong, healthy tree. When the desert rose has been freshly repotted, or it comes out of dormancy, I water once a week until I see green emerge from the branches, and then I start to water every three days until I see a flower emerge. That’s when I will start to water my desert rose daily. It is essential that the desert rose is placed in a very hot spot, and once it stops blooming, I go back to watering every three days. Once autumn approaches, I will stop watering almost completely, only watering lightly once a month.
It is extremely important that you stop watering in autumn and put your desert rose to sleep manually. Continue to water your succulent throughout the entire year and one of two things can occur: root rot when it’s no longer as hot, or exhaustion. Desert rose is just like any other tree and can become exhausted by growing too much throughout the year. That will affect the plant in the following year.
If you want to grow a strong and healthy desert rose you have to make sure that you put it to sleep and that it gets its rest. This watering schedule applies only to a coarse soil mix, which is what we recommend. We use an all-purpose soil mixture. It consists of lava rock, pumice, some calcined clay and pine bark.
Wiring: Desert roses can be easily wired using aluminium wire. For thicker branches use a double gauge of wire to bend the branch easily in the desired position.