The genus Adenium is a member of the family Apocynaceae and originates from Africa, south of the Sahara from Senegal to Sudan and Kenya, and through Saudi Arabia, Oman, and Yemen (Oyen, 2008; Plaizier, 1980). Commonly known as desert rose, the genus is prized for its attractive floral array atop a swollen, sculptural caudex (Rowley, 1987). As roots mature they swell and enlarge along with the caudex and add an important sculptural element that compliments the flowers; therefore, root formation is an important measure of aesthetic value for this crop (Dimmitt et al., 2009). Adenium plants in a wide range of architectural forms, growth habits, and flower colors are available for sale globally. However, there is no scientific literature regarding Adenium cultural requirements. Production of Adenium species under a minimum PAR of 1000 to 1600 μmol·m−2·s−1 and a temperature range of 30 to 35 °C (85 to 95 °F) with high humidity during the growing season has been suggested (Dimmitt, 1998). It also was reported that Adenium responded well to a balanced fertilizer such as 20N–20P205–20 K20 plus micronutrients at a concentration of 200 mg·L−1 N (Dimmitt, 1998); however, no data were presented.
A limited number of nutritional studies on other herbaceous genera within the family Apocynaceae has been published. Plumeria rubra grown in pure silica sand in 4-L containers were treated with a low and high nutrient level (2.4 g and 24.0 g, respectively, of 14N–14P–14K of Osmocote®) in a glasshouse for 60 d during August and September (Huante et al., 1995). In that study, more biomass was produced under high nutrient supply, whereas more biomass was allocated to the roots in low nutrient supply.
Mandevilla Vogue varieties were shown to be moderate feeders, responding best to use of a balanced fertilizer at a rate of 100 to 200 mg·L–1 and it was recommended that a low to medium rate of a standard slow-release fertilizer should be added at planting (Mart, 2012). In a study testing the effects of Sumagic® (uniconazole) on the growth and flowering of Mandevilla ‘Alice Du Pont’, Deneke et al. (1992) chose 8.3 kg of Osmocote® (18N–6P–12K) per cubic meter of potting medium. Plants were also liquid fertilized weekly with 300 mg·L–1 N from 20N–4.3P–16.6K (20–10–20). In an experiment conducted with Dipladenia sanderi L. (Plaza et al., 2009), fertigation was applied in a nutrient solution containing with a pH of 7.2 and an electrical conductivity of 1.2 dS·m–1. Established landscape plants of Allamanda cathartica ‘Hendersonii’ were used in an experiment testing four different fertilizers on growth and quality (Broschat et al., 2008). The authors concluded that Allamanda in the landscape may not benefit greatly from increasing fertilization.
Vinca (Catharanthus roseus L.) seedlings benefitted from high concentrations of N (up to 32 mm) in the fertilizer, whereas only low concentrations of phosphorus and potassium (0.25 mm) were needed (van Iersel et al., 1999). Kessler (1998) indicated that plug-grown Vinca seedlings should be fertilized once or twice a week with 50 to 75 mg·L–1 N. Nitrogen levels could be increased to 100 to 150 mg·L–1 once true leaves develop.
To determine the cultural requirements for producing good-quality desert rose plants in containers, the following study was conducted to determine effects of light and nutritional levels on growth and flowering of Adenium obesum ‘Red’ and ‘Ice Pink’, two cultivars that are in commercial production in Florida.
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DimmittM.G.JosephG.PalzkillD.2009Adenium: Sculptural elegance floral extravagance. Scathingly Brilliant Idea Tucson AZ
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