The Desert Rose
Some gardeners in South Florida are reluctant to plant succulents, believing that all succulents come from deserts and won’t grow here, or have undesirable spines, or are uninteresting.
In fact, many succulents are well suited to our seasonally dry climate and fast-draining soils. They can have extremely showy flowers, great color and striking forms. Above all, the survival strategies of succulents are some of the most amazing of any plants.
One succulent that does especially well here is Adenium obesum, popularly known as the desert rose for its large, brightly colored flowers. Wild forms of the species can be found in Kenya, Somalia, Saudi Arabia, Yemen and Oman. Some are small shrubs, others large, and others tend to grow as small trees. Adeniums belong to the larger plant family that includes Plumeria or Frangipani. Like frangipani, the desert rose is the subject of intensive selection and breeding programs to produce all sorts of horticultural cultivars. Flower color, patterns and size have been greatly modified from wild ancestors, often resulting in additional secondary changes to the overall form of the plants. All have similar horticultural needs.
Grow adeniums outdoors in full sun, in well-drained soil. Adding some non-limestone rough gravel, such as lava rock or expanded shale, to the mix is a good idea. Coarse silica sand can also help with drainage. Adeniums tend to be quite sensitive to frost, so you must protect them from turning to mush on the coldest South Florida nights.
They are great in pots, especially terra cotta, that offer quick evaporation and gas exchange for their roots. Use a porous mix that incorporates plenty of perlite and/or gravel to speed drainage. If the wet potting mix won’t hold together when squeezed by hand, it’s the correct porosity. Whether planted or potted, mulching adeniums with gravel is a natural and attractive way of displaying them. Give them a slow or controlled-release fertilizer that contains some microelements and is fairly low in nitrogen, such as 8-2-12. Even 10-10-10 or 7-7-7 will work, as long as the nitrogen isn’t too quickly available for the plants. Water these heat- and light-loving plants regularly during their active summer growing period. To prevent rot, they must be allowed to dry out completely between watering.
Adeniums tend to go semi-dormant in the winter, losing most or all of their leaves. They don’t need much water during those times, but they also don’t appreciate being bone-dry for months on end. They do like an occasional soaking drink, as long as they can dry quickly. Underneath its silvery-grey stem is a thin green layer that continues the job of photosynthesis, even without leaves.
Horticultural varieties of desert roses, especially grafted plants, don’t seem to produce the same thickening at their base (caudex) that wild forms are famous for. Some greatly resemble their frangipani relatives by not thickening at all. If a thick base is desired for display, gradually remove some soil and raise the level of the plant in its pot or replant it in its bed with a portion of its roots exposed. Doing so will not cause harm as long as freshly severed roots are kept dry to prevent rot.
Harvey Bernstein is the horticulturist at Pinecrest Gardens.