The Beautiful Desert Rose How to Grow and Flower Adeniums
By Laurelynn Martin and Byron Martin
Adeniums are well-loved for their gorgeous flowers and their bulbous, caudiciform trunks. They are highly sought after plants and can remain a manageable size for years making them valuable container plants.
Adeniums are arid land plants native to sub-Saharan Africa and although there are several species, Adenium obesum is the one that's frequently grown as an ornamental. The common name is Desert Rose and when plants are in bloom, they create a spectacular floral display.
When grown from seed, the plant forms a caudex, or swollen base or trunk, and this adds to its ornamental beauty. In recent years, much hybridization has been done creating a diverse range of flower colors and interesting floral forms. In order to propagate these hybrids, the mother plant is grafted onto a seedling, thus giving the plant a full, attractive caudex as well as a wide array of flowers in various colors, sizes and shapes.
Because they can tolerate dry conditions, adeniums are well suited for the home environment being able to tolerate quite a bit of neglect. Keep temperatures high, preferably above 60˙F, although they can take it a bit cooler if grown very dry. Really the hotter, the better, so a 70˙F or higher air temperature is best.
In their native habitat, adeniums grow in full sun so they need good light to thrive. Direct sunlight is preferable, especially when they are in their active growth phase during the summer months.
Soil moisture is an important consideration in adenium culture. Their common name, Desert Rose, speaks to their ability to thrive with less water. Adeniums can tolerate higher moisture levels without harming the plant, as long as the temperatures are warm. As a general rule, be sure to let the soil dry out in between wateringsand then thoroughly saturate the potting mix. Do not over-water adeniums when they are in their inactive growth phase during the winter months. If the soil is kept too moist, root disease can become a problem. During the slow growth time of year, it is best to water adeniums sparingly and err on the dry side. Once temperatures and day length have increased and new growth is visible, increase the amount of water. This will stimulate growth and flowering. Under very dry conditions, the plants can defoliate completely. Although somewhat unsightly, it does no harm and the plant will bounce back. A good rule to remember when growing adeniums is that high temperatures and full sun require more water and in cooler temperatures, the plants need less water.
Adeniums should be fertilized when they are actively growing during the spring and summer months. We recommend a balanced fertilizer with an elevated middle number (phosphorus) to assist in flower formation. There is a critical balance between too much and too little fertilizer since these plants are sensitive to elevated fertilizer salt levels in the soil. This can be seen on the plant with the symptomatic browning of the leaf edges. Generally, when watering succulents or other arid plants, the amount of water given should saturate the soil mix but there is often very little extra water moving through the soil. Therefore, when frequent doses of liquid fertilizer are applied, toxic levels can build up in the soil. For this reason, it's a good idea to periodically leach the soil with clear water by watering until you see water draining out of the bottom of the pot.
The only reason to prune your Desert Rose is for size management and to sculpt a nice shape. If you do prune, make sure this is done at the beginning of summer so the wounds heal and new growth will have time fill out the plant's form.
Spider mites are the greatest challenge as far as insects go. Since adeniums can tolerate dryness, and really need it, it's the perfect place for spider mite populations to grow and expand. Check your plants regularly for beginning infestations, especially when plants are brought in for the winter and they are subjected to warm, dry conditions. Mealy bugs can also affect plants but generally this is because there are other infected plants nearby.
Getting Rid of Pests
Spritzer method - Mist the undersides of the foliage; this discourages spider mite populations. However, make sure you do not over-wet the soil from misting the leaves. We recommend using a spritzer on a daily basis for a week or so. This has proven to be an effective technique to keep spider mites under control. Neem Oil - Neem is a natural pest control that's also a good choice for adeniums. It works by smothering the pests. Predatory mites - Predatory mites, Amblyceius californicus, work well under dry conditions. However, Amblyceius californicus is slow working and is only suitable for a small mite infestation.
Root disease can be deadly for adeniums. If the caudex gets soft, the plant may die. The bacteria and fungi that cause root diseases enter the plant mostly from over watering or poor drainage. Let the soil dry out between waterings, and maintain dry, well-drained soil, similar to their native habitat, especially during the cooler winter months to prevent root problems.
Important Advice for Successful Growing
Grow adeniums in warm temperatures and on the dry side. Over time and with repotting add fertilizer as described above. This will promote flowering and encourage the caudex to enlarge. Keeping the plant cramped in its pot will result in a smaller specimen that you can maintain as a windowsill-sized plant for a very long time. Adeniums also make great bonsai specimens.