Adenium is a genus of flowering plants in the dogbane family, Apocynaceae, first described as a genus in 1819. It is native to Africa and to the Arabian Peninsula.
WATERING: Adeniums, like all succulent plants, have the ability to store water. In their native habitat they live and grow only on the available rainfall, storing water in wet times to sustain them through drought. In extreme drought, even during the growing season, they can drop their leaves and become ‘drought dormant’, only to re-leaf with the first available moisture. These arid conditions do not adversely affect the plants other than to cause them to grow more slowly. This is a characteristic to be taken advantage of in cultivation. Adeniums can be left for long periods (the larger the plant, the longer the time) without the need to be watered and only suffer a setback in growth, but no adverse effect on the health of the plant. However, it is extremely important to realize that a container grown plant has its entire root mass confined to the pot, (unlike a plant in the ground that can actually grow roots in search of available soil moisture) and so is dependent on an outside source of water (YOU!) to survive and grow.
FERTILIZING: Under natural conditions plants utilize nutrients in the soil they grow in and to a limited degree will grow roots into ‘fresh’ soil when needed. In a container a plant can use up the available nutrients in a relatively short time. When these nutrients are depleted, growth slows and in the extreme will stop or become distorted. Also, nutrients are leached out of the soil with watering. Under ideal conditions (usually only achieved in the nursery) Adeniums can be fertilized with what amounts to a full strength application of a general purpose fertilizer every two weeks. Under most home conditions, and only if the plant is healthy, a half strength solution applied once a month during the growing season (April – October) of any available house plant food will be adequate.
TEMPERATURE: In their native habitat, Adeniums are not subject to freezing temperatures. Here in the arid southwest we regularly experience sub-freezing temperatures. (Tucson averages twelve nights below 32°F.) This is a major consideration in growing Adeniums. They must not be allowed to freeze! Most often this is simply a matter of moving the container to a protected location. If possible it is desirable that the plant have good light throughout the winter, such as that available through a sliding glass door, just inside the house from the patio. The further into the house the plant is, the less light available to it. If overwintered inside, unless it receives very bright light, an Adenium should be allowed to go dormant. If home nighttime temperatures stay above 55°F, dormancy may need to be forced by withholding all water until the leaves drop. If indoor night temperatures are too high (70°F) the plant may try to grow. This is an undesirable situation causing weak, etiolated (thin, light-seeking) growth and an alternative overwintering area should be found. If a plant does experience this type of growth, it is best to prune it off after being moved outdoors in the spring.
SOIL and POTTING: The basic characteristic of potting soil for Adeniums is that it be well drained. This means that water should drain through the soil in a matter of seconds after being applied. A good potting mix with the addition of an equal part of pumice or clean, small gravel (preferably granite) will work well. Good commercial ‘cactus’ mixes are available. There are many recipes for soil and every grower will use a different one. It is a good idea to find one that you and your plants like and stick with it as your cultural habits (watering and fertilizing) are somewhat dependent on the soil mix used.
Adeniums will tolerate being pot bound without ill effects. They can continue to grow roots to the point of distorting plastic pots and even breaking clay or stoneware pots. Repotting Adeniums should be done only during the growing season and not late in that season. When repotting is desired, it is usually a simple matter of putting the plant, with its rootball intact, into a larger pot and filling in with the soil mix, making sure not to bury the plant deeper than it was. Since these plants usually have a large root/stem just below the soil line, some of this can be exposed by removing a layer of soil and filling in beneath the plant to raise it up. Removing the old pot can sometimes be a problem and occasionally a hammer may be needed to break apart the old pot. Adeniums can be watered within a day or two of repotting.
PESTS and DISEASES: In cultivation Adeniums are rarely subject to diseases, but are occasionally hosts for one of three insect pests. Mealy bugs, aphids and spider mites can all inflict damage on these plants. Although usually not serious, these pests can cause distorted growth and ruin flowers and flower buds. Outdoor growing (plants love good air movement) in most cases will prevent these problems, but occasionally an infestation will occur. For spider mites and aphids a jet of water aimed to physically dislodge the pests will often suffice. This treatment may need to be repeated several times for complete control. If the mealy bugs are not overwhelming, a cotton swab dipped in alcohol will kill all of them that it touches. This should also be repeated for several days. There are numerous commercial preparations available for these insects, but it is best to avoid their use if possible because of the possibility of harm both to your plant (phytotoxicity, time of day of application, dilution rates) and you.