The Adenium obesum is a deciduous, shrubby stem succulent within the Apocynaceae family. It’s native to Sachel regions south of the Sahara Desert, Eastern and Southern Africa, and Saudi Arabia. This frost-tender succulent has adapted to harsh, hot, dry deserts with limited water and nutrients.
These “rock roses” are closely related to the Oleander genus, and are quite easy to grow. They also have many points of interest for cacti and succulent collectors. Their unusual growth form, stunning tubular flowers, and glossy ovate leaves are particularly stunning.
They’re also used successfully in the fascinating art of bonsai growing around the globe.
Adenium obesum’s Growing Form
This plant’s stature is unique, with a large, swollen base, (also known as the caudex). In fact, it shows little differentiation between its chunky trunk and short, finger-like, upright branches. Plants may be slow-growing, but are long-lived when given the right care.
A Stem Succulent
The caudex is a storage organ that contains all of the water and nutrients needed to survive its dry, arid natural habitat. Growing forms vary from habitat to habitat, but where other plants may diminish, the hardy Adenium thrives. It can often be spotted growing squashed between granite rocks and cliff faces.
Let’s find out more about this stunning succulent. We’ll delve into its growing needs, alternative species, and why we have a soft spot for these quirky plants.
Due to its widespread origin, the Adenium obesum has many namesakes. Its most popular is “desert rose”, which references its ornate, beautifully colored mass of tubular flowers. Further common names include the “mock azalea”, “rock rose”, and “sabi star”.
There are now many Adenium varieties, most being direct descendants of the “obesum”. It’s been extensively hybridized in recent years, resulting in further subspecies. I’ve listed a couple below that are of personal interest, but take a look for yourself. You’ll discover the wonderful variety of showy flowers and growing forms available.
This cultivar is native to Oman and the adjacent mountains of Yemen. It has large, glossy, thick oval leaves and verysmall trumpet-shaped pale pink flowers. In its native home, this species is only in leaf for three summer months when bathed in a continuous mist from the edge of the Asian Monsoon. The Adenium dhofarense has numerous branches rising from a low, wide caudex, but is a less popular plant choice for home growing.
This has a common name of “Impala Lily” and “Sabie Star”. It’s commonly found growing at low altitudes in hot, dry, sandy habitats, but also open deciduous woodlands. Naturally found in southern Africa, it extends into eastern and western tropical Africa.
The Adenium multiflorum has the typical thick caudex stem, smooth grey-green branches and beautiful large pale pink or white flowers with a pink to deep red border. Flowering lasts from May to August, soon followed by glossy green leaves, each with a lighter midrib. These leaves densely crowd the branch tips. This species will grow to a height of up to 3 meters, and its Latin name means “many-flowered”.
With a similar growth structure to our Adenium obesum, this species bears multiples of flared, tubular flowers ranging from bright pink to carmine red. These often appear before the leaves and generally remain open for only 2 to 3 days. In fact, it’s not uncommon to see a crown full of blooms but no leaves at all. Thankfully, with each bloom at 5 cm, you don’t actually notice the lack of leaves.
Hybrid Growing Forms
Many hybrid varieties of this delightful succulent have contrasting foliage and flowers from those mentioned above. Leaves tend to be narrower, though still oblong in shape. Most have a prominent white mid-rib vein and positioned in spiral clusters towards the tips of the branches.
Adenium flowers are like brightly colored trumpets. The flower veins and margins are a deeper tone than the flowers themselves, and are produced in clusters on grey-green branches.
Rock Rose Fruits
This species’ fruit capsules clearly resemble a pair of steer horns. These are pale green in infancy , maturing to a duller shade of grey-brown. Once fully mature, the capsules burst, releasing hundreds of long, narrow seeds. Each seed can reach up to 14 mm long and has a hairy tuft at each end.
When blown along the ground, the effect is similar to an axle with two wheels.
I’m sure this “hairy tuft” is another adaptation of nature. An evolutionary genius made to ensure the continuation of this unique species.
Planting your Adenium obesum
Choosing the Perfect Growing Medium
I recommend using a typical, free-draining succulent compost when planting your rock rose.
Site and Temperature Requirements
Keeping a steady temperature of at least 15C/59F from spring to autumn, will promote strong new growth. Furthermore, it’ll help your Adenium thrive.
Reasonably high humidity is also required throughout the growing months. This can be achieved by regularly misting your plant, or by placing your plant on a pebble and water-filled plant tray. Once the growing season is over, your plant won’t need this high humidity environment.
These stem succulents like a bright and sunny spot, which in turn will promote better flowering Throughout the winter months it’s important to let your Adenium rest by keeping it dry. Ensure a minimum temperature of at least 10C/50F is maintained at all times.
Caring for your Adenium obesum
We know that as a succulent, your Adenium is an extremely drought-tolerant specimen. I recommend using the same watering rule for all succulents and cacti that originate from hot, arid regions.
Throughout the growing season, water your plant well, letting the excess drain away from the pot. After a period where the potting medium has dried out, water again.
The worst thing you can do to any succulent is to allow your plant to sit in water.
Feeding your Adenium
There’s a fertilizer specially formulated for the “desert rose” succulent, containing the right balance of nutrients for optimal absorption. Alternatively, you can use an organic seaweed fertilizer or specialized succulent feed. Always read the diluting instructions before use.
In the springtime, feed it once every two to three weeks. As the summer arrives, reduce this to once a month. As the weather cools down for the winter, you won’t need to feed your Adenium at all.
These succulents can grow up to around 6 feet in height and up to around 2 feet wide. Regular pruning will keep your plant in good health and at a manageable size.
Throughout the growing season, pinch out any unruly new growth, keeping your plant in good shape. At the end of the growing season, remove any dead, dying, or diseased branches. Take out any growth that isn’t beneficial to your plant’s shape.
It’s possible to grow another desert rose from cuttings taken from your mother plant. In this case, you won’t see a swollen caudex develop above soil level. After a time, you can lift semi-mature cuttings and unearth the storage organ from below the ground. At this point, you can replant with the caudex on full show. Note that this won’t cause any damage to your plant.
Alternatively, there are many species of seeds available, all with different qualities but beautiful tropical flower clusters. Plants grown from seed produce the most amazing caudex shapes of caudex. This can give the grower a great sense of satisfaction.
All Adenium succulents produce a poisonous sap within their roots and stems. This poison contains cardiac glycosides and is highly toxic to pets and people. Throughout native Namibia, the Heikom Bushmen commonly use this sap to poison arrows for game hunting.
Good cultural practices can prevent a number of pest and disease problems.
Adeniums are subject to a few common pests in cultivation. Mealybugs, aphids, spider mites and scale tend to be the worst offenders. Fortunately, all can be treated with a suitable pesticide or the organic alternative.
Warm, moist growing environments can be ideal site for pests to multiply and prosper. To avoid infestations ensure your plants are given enough space, good air circulation, and a clean growing environment.
Over-watering is the commonest cause of disease problems in Adeniums. Remember these succulent plants are natively able to survive on very little amounts of water and nutrients. Though they like reasonably high humidity, try to avoid constantly wet leaves and badly aerated growing mediums. Both problems can lead to plant rot.
Using a well-draining growing medium promotes a healthy root system and growing cycle. Just note that this can also lead to possible nutrient leaching. This means plant nutrients are washed through the soil before your plant can use them.
Typical nutritional problems can show themselves in a variety of ways:
- Yellowing leaves and subsequent dropping of lower leaves is a sure sign of nitrogen deficiency
- Potassium deficiency shows as edge burn on the lower leaves and leaf drop
- Red tinting of the leaves and poor growth is a sign of a phosphorus deficiency
- Calcium deficiency symptoms include leaf-tip burn, blackened new leaves and tip death
There are further micro-nutrients which can cause additional problems, but the main problems are those listed above.