Allamanda Flowers
Also called golden trumpets or simply allamandas, plants in the genus Allamanda produce their trumpet-shaped flowers with five spreading lobe-petals when temperatures are warm. Native to Central and South America, allamandas do not tolerate frost and need lots of sunshine and heat to reliably produce blossoms. Grow plants outdoors in the ground in U.S. Department of Agriculture plant hardiness zones 9b and warmer. Elsewhere, use them as seasonal plants that die once frost and subfreezing temperatures occur in fall. Bring container-grown allamandas indoors to overwinter. Does this Spark an idea?
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Species
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American nurseries and garden centers most often sell three species of allamandas, the golden trumpet or brownbud allamanda (Allamanda cathartica), the purple allamanda (A. blanchetii) and the bush allamanda (A. schottii). All contain milky white sap that is poisonous if eaten and may cause a rash on sensitive skin. Golden trumpet produces large yellow flowers, 5 inches wide and 3 inches long. Purple allamanda flowers are a bit smaller, 4 to 4 1/2 inches wide and 3 inches long. Flowers of the bush allamanda are smallest, only 2 1/2 to 3 inches wide and 2 inches long.
Cultivars
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Within each allamanda species, horticulturists selected mutations that produced more ornate flower or growth characteristics and gave them cultivar names. Cultivars are propagated asexually to produce clone plants with the exact same qualities. Two cultivars of the golden trumpet are of note. Flore Pleno produces flowers with extra petals and look like ruffled cones. Hendersonii yields large flowers with bright canary yellow color, occasionally blushed with golden orange. The purple allamanda naturally displays rosy violet flowers with dark throats. However, cultivars Chocolate Cherry and Chocolate Swirl produce flowers with pinkish purple flowers with burgundy-brown throats. Cherries Jubilee bears creamy burgundy violet blossoms.
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Flowering
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Allamanda plants produce small clusters of flower buds from the leaf bases near the tips of their stems. The buds open in succession, so usually no more than two flowers are open at a time in each bud cluster. The golden trumpet and purple allamanda plants tend to hold the flowers horizontally, although a downward blossom isn't uncommon. Each blossom resembles a trumpet or bell, depending on how it is oriented from the stem. Flower production increases as temperatures stay in the 65 to 85 degrees Fahrenheit range. Cool or excessively hot weather reduces or inhibits profuse flowering. Flowers arise on new growth, so do not prune branch tips.
Blossom Structure
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An allamanda's flower bud elongates with a slender tube at its base. At the bud's tip is a swollen area that contains the floral sex organs, protected by the petal tissues. As the flower mature, the petal tissues separate into five wide, oval lobes. The petals fuse at the bases into a cuplike or trumpet throat. Deep inside the throat, five short stamens shed pollen onto the two-lobed pistil tip. The female pistil contains two cells, both with numerous ovules that become seeds after the flower is pollinated by hummingbirds or long-tongued moths.
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