Dramatic container plants, desert roses (Adenium spp.) are succulent members of the oleander family usually grown as a succulent bonsai. The swollen, water-storing plant base, stems and branches lend character even to younger plants. Plants go dormant and drop their leaves in winter, revealing a pale gray trunk and branches. Showy red, pink or white flowers appear in late winter to spring, often while the plant is leafless. Native to Africa and Arabia, desert roses don't survive temperatures below 32 degrees Fahrenheit.
Kinds of Desert Rose
One of the most widely available desert rose species is Adenium obesum, hardy in U.S. Department of Agriculture plant hardiness zones 10b through 12. A number of hybrids are available, and some have double or triple flower forms and combine two or three colors in a flower. About seven or eight other desert rose species exist, but some of them are rare and hard to obtain.
In keeping with its desert origins, during spring and summer when desert rose is actively growing, it needs full sun to light shade. During winter dormancy, plants can tolerate bright indirect light. If you bring the plant indoors for overwintering, a south- or west-facing window works best.
Unless you live in a completely frost-free climate, you'll want to grow desert rose as a container plant so you can move it indoors to protect it from cold. Use a well-draining potting mix suitable for growing succulent plants or make your own mix with equal parts quality soilless mix and either perlite, sand or poultry grit. Make sure the container has drainage holes in the bottom.
Select a container just slightly larger than the root mass of the desert rose. Replant every year or two into the next largest pot size until the desert rose reaches the size you wish to maintain. In keeping with the bonsai character of desert rose, choose a relatively shallow container for larger plants such as a bowl-shaped pot. This gives the roots lateral expansion room and allows the soil to dry out more quickly.
In the spring and summer when desert rose is actively growing, it needs regular watering. Because the plants store water, the soil doesn't have to be kept moist; in fact, continuously wet soil can lead to root rot. Allow the top 1 to 2 inches of soil to dry between waterings. With each watering, give enough water so it comes through the pot's drainage holes.
When plants are dormant, usually watering once a month is sufficient. If you're keeping overwintered desert rose in temperatures below 50 degrees F, don't water them at all.
From the time desert rose begins to leaf out in the spring to the end of summer, feed it weekly with a balanced fertilizer at half the usual strength. Adeniums do not like to be in wet soil during cold periods. For water-soluble 20-20-20, apply 1/4 teaspoon of fertilizer for each 2 quarts of water.
Over time, desert rose can grow to be a small tree. Restrict its size by consistently underpotting the plants. Keep the growth form compact by giving desert rose sunlight. Prune plants during spring or summer to maintain their height or to shape the branch structure. Wear waterproof gloves and protective clothing because the sap is toxic and can irritate your skin. Before pruning, clean the shears with a cloth soaked in rubbing alcohol. Wash the pruners and gloves right after use in warm soapy water, rinsing well.
A few sap-sucking pests such as aphids, mealybugs and mites can feed on desert rose. They're more likely to get started on plants kept constantly indoors or in greenhouses. Aphids are soft-bodied insects about 1/8 inch long, often yellow in color on desert rose. Mealybugs are usually oval, flattened gray to pinkish insects less than 1/4 inch long that settle in on stems and leaf undersides. Mites are very small; you'll probably see their webbings or the small, pale spots they leave when they feed on leaves rather than the mites.
Combat these pests with vigilance. Inspect your desert rose every week or so, looking for pests. As soon as you see aphids or mites, wash them off with a strong spray of water. Stressful conditions such as dryness are contributing factors to mite infestations, so keep the desert rose in good health. Remove mealybugs and aphids with a cotton swab or a piece of soft cloth moistened with soapy water.