A succulent small tree that does not tolerate frost, the desert rose (Adenium obesum) forms swollen trunks that resemble elephant ankles. Potentially reaching 15 feet in height in the wild, most garden-raised plants grow substantially smaller, whether in the ground or in decorative containers. Also called impala-lily or kudu-lily, its blossoms are colored pink to white. Grow it outdoors in USDA Hardiness Zones 10 and warmer.
The desert rose tree hails from the seasonally wet to dry lands of eastern Africa and the Arabian peninsula. Subspecies swazicum grows naturally only in the southern African regions of Swaziland and KwaZulu-Natal. Most desert roses grown in gardens today are hybrids, according to Kirsten Albrecht Llamas, author of "Tropical Flowering Plants."
The smooth, gray-tan bark of the desert rose adds an exotic, contorting feel to the plant when deciduous during the dry or winter season. The base or caudex swells into a massive, plump base, the result of alternating seasons when soil moisture is absent or abundant. The fleshy, firm water-retentive stems and trunk allow it to survive intense heat and drought. In spring and summer, as rainfall begins to increase, long oval leaves again adorn the branch tips, as do clusters of flower buds. Each blossom usually lacks fragrance and becomes a five-lobed trumpet when fully open. Their color ranges from white to pink shades, with or without contrasting edges of color or fringe. Some hybrids bear deep red blossoms or ivory with pale yellow centers.
Grow desert rose in a fast-draining soil that is neutral to slightly acidic in pH (6.0 to 7.0). Sand-based soils with organic matter provide ideal growing conditions. Do not allow this plant to experience frost or freezing temperatures and it tolerates temperatures below 45 degrees Fahrenheit only when soil remains dry. Over-watering leads to root and stem rot. In the intense sunlight and heat of summer, water more frequently and fertilize to promote flowering and production or retention of foliage. In winter refrain from watering. Plants must receive at least 8 to 10 hours of direct sunlight daily year round.
Although people think succulent plants should never receive water, providing one-inch of irrigation weekly to a desert rose in summer promotes lush growth and flowering. The abrupt ending of watering in fall and winter during a dry season encourages the trunk and branches to swell and retain moisture. If this annual alternation between hot and moist and cool and dry does not occur, the plant grows slowly and the swollen trunks fail to develop well.
Propagate desert rose by planting seed or by taking stem cuttings and rooting them in warm, damp sand. Plants grown from seed develop swollen trunks while those raised as cutting fail to ever develop swollen bases, unless the cuttings are grafted onto plants grown from seed.
As members of the dogbane family, Apocynaceae, desert rose sap is milky and contains alkaloids. Some people will develop a rash when in contact with the sap. Do not eat any part of the desert rose.