Long, pendent, bell-shaped flowers that look like miniature ball gowns grace the branches of angel's trumpets (Brugmansia spp.) during the warm months of the year. Frost-free conditions and a fertile, moist but well-drained soil allows these tropical shrubs to prosper. In U.S. Department of Agriculture plant hardiness zones 10 and warmer, angel's trumpets become small trees up to 20 feet tall. In zones 8 and 9, winter frosts kill back plants but they survive the mild winters and sprout again in middle to late spring. Fertilizing ensures the best flowering cycles.
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Fertilizing angel's trumpets properly is made easier if the garden soil contains the right blend of organic matter and soil particles. Angel's trumpets must have an evenly moist but well-drained soil. Sandy soils leach water and nutrients too quickly, while clay soils can become compacted and create wet conditions that rot roots. Incorporate generous amounts of compost and well-rotted manure into the soil before planting an angel's trumpet. Also place a 3-inch layer of organic mulch atop the soil to retain moisture, prevent weeds and provide trace nutrients to the plant roots.
The use of granular, slow-release fertilizers ensures the long-term supply of nutrients to angel's trumpets. Coupled with organic matter, a soil dotted with granular fertilizer provides an even, constant supply of basic nutrients to keep the angel's trumpet growing in good health any time of year. Any balanced, general-purpose landscape formula suffices, such as 8-8-8 or 10-10-10. These products decompose to release nutrients to plant roots over two to six months. Products such as Osmocote and Nutricote/Dynamite are particularly good for angel's trumpets as long as soil temperatures remain above 60 degrees Fahrenheit. Although beneficial, using slow-release fertilizers alone does not tend to yield the best flowering displays.
Organic matter and slow-release fertilizer granules atop the soil around an angel's trumpet provide a solid nutritional base. When warm weather dominates and the plant is actively growing by adding new leaves and stem length, supplement with fast-acting water-soluble fertilizers. Angel's trumpets are "heavy feeders," meaning they respond well to lots of nutrients and water during the warmest months of the year. Follow product label directions for mixing the formulations, and apply the solution to the base of small angel's trumpets once per week. Larger plants can benefit from the liquid feeding two to three times a week during the height of summer. Peter's Professional 10-10-10 or any Miracle-Gro product works well, according to Richard R. Iversen, author of "The Exotic Garden."
Always apply liquid fertilizer solutions to a moist soil. Fertilizers poured onto dry soil can cause angel's trumpets' roots to burn from the contact with the fertilizer salts. During the warm months, angel's trumpets benefit from the application of Epsom salts, also known as magnesium sulfate. Use 1 tbsp. per gallon of water and apply it once a month. Do not fertilize angel's trumpets in fall and winter when temperatures cool down and the plants stop growing or begin to yellow and drop foliage. Keep the soil slightly drier in winter to avoid any root fungal diseases.