Desert Rose

When you look at a blooming desert rose (Adenium obesum), you might swear that you are looking at the pink pinwheel flowers of oleander, mandevilla or annual vinca that have been pasted onto the thick and succulent branches of a plant whose leaves resemble those of a carrotwood (Cupaniopsis anacardioides). Yet the flowers have not been pasted on, although there is a family connection between the desert rose and the just mentioned plants that carry look-alike blooms.
All of the above pinwheel flowers belong to the dogbane (Apocynaceae) family, which cause gastronomic distress and can even be fatal to dogs (or people) who chew on their branches. For this reason, it is best to dispose of prunings immediately and not leave them on the ground.
Care of the desert rose requires a specific soil and watering regimen. The soil mix of this container-grown plant should be one-half perlite or pumice and one-half potting soil. Mulch the soil surface with pumice or fine gravel so that the soil dries out evenly. Water only when the soil is nearly, but not completely, dry.
To save yourself the worry of determining when this occurs, procure a water meter at a nursery for under $10. The point is not to allow the desert rose’s hydrophobic soil to go bone dry, as it is difficult to re-wet. When the temperature reaches 80 degrees, the plant should still not need to be watered more than once a week. With each watering, fertilize at one-quarter the recommended strength. (If Miracle-Gro recommends 1 tablespoon per gallon of water, use one-quarter tablespoon per gallon instead.) Flowers are produced continuously on this cactuslike plant from spring until fall.
Desert roses should be grown outdoors. The only problem is that they can die when temperatures dip below 40 degrees. To protect against this possibility, put plants in a greenhouse window or other very sunny exposure indoors during the winter, or at least bring desert roses inside at night starting around Thanksgiving. Adeniums go dormant as days get increasingly shorter in the fall, when they lose their leaves, and they should not be watered again until the return of much longer days, heralding the approach of spring.
You can propagate the desert rose from cuttings but such cloned plants will be without the telltale caudex or swollen trunk that is part of the plant’s personality. If you want a caudex, you must grow the desert rose from seed. Since desert roses are not self-fertile, however, you will need at least two of them for cross-pollination and seed production to occur. Use a small paintbrush to transfer pollen from flower to flower.
In the Valley, the two most outstanding perennial bloomers for late summer and early fall, whose species name is capensis (meaning “of the cape” in Latin), come from South Africa’s Cape of Good Hope.
Cape honeysuckle (Tecomaria capensis) is not a true honeysuckle, although its flowers do have the swoop and extruding pistils of true or common honeysuckle (Lonicera species).
Cape honeysuckle does best where it can grow unkempt and without competition, such as on slopes where its aggressive roots prevent erosion, or against long fences or walls where a carefree vinelike grower is needed. The most commonly seen cape honeysuckle has orange to orange-red flowers, but yellow and salmon varieties are also occasionally encountered. It will bloom in both full and partial sun exposures.
Blue plumbago (Plumbago capensis) displays a plethora of sticky, baby-blue flowers in summer and fall. This billowy shrub is commonly seen in freeway plantings and, like cape honeysuckle, will grow rampantly with a minimum of care in full to partial sun. White and royal blue varieties are also available.
Black-eyed Susan clock vine (Thunbergia elata) is a rapid grower with vivid orange flowers – you sometimes see them in pale yellow – that cannot be stopped except by cold weather. A less well-known relative is Bengal clock vine (Thunbergia grandiflora), whose large lavender to deep blue flowers are without equal. Clock vines grow rapidly and, planted in early spring, can produce six to eight feet of growth and a myriad of flowers before cold winter intervenes. Although of tropical origin, Bengal clock vine will persist from year to year if it is planted against a wall or under an overhang where it will benefit from an extra measure of radiant heat on cold nights.
Tip of the week
If you are looking for a long-blooming stand-alone shrub that is perfectly suited to patio or balcony containers and for spilling over block walls as well, consider coral fountain (Russelia equisetiformus). The stringlike, leafless green stems of this 4-foot-tall shrub do, indeed, arch and spill over like a fountain, and its flowers are red to scarlet. Coral, when used in plant appellations, does not mean pink but refers to a color spectrum that stretches from burnt orange to brilliant red, the same colors seen in the flowers of coral trees (Erythrina species). Coral fountain can be grown in full to partial sun. It begins to bloom in late spring and continues to flower throughout the summer and into the fall. It does have limits where winters are cold, although it will survive a freeze in locations where it is protected by overhanging tree branches or the eaves of a roof. Coral fountain responds well to monthly fertilization during the growing season. Preparing the ground with well-drained topsoil and compost prior to planting will result in reduced fertilizer and water needs and a greater tolerance to cold.

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