Plant Devil's Trumpet seedlings approximately 2 feet apart in rich, drained soil that gets daily exposure to full sunlight. Giving the flowers this room will ensure that they are able to reach their full height, which will reach anywhere from 2 to 3 feet. Wait until one week after the last frost before planting this annual to ensure it survives.
Water the plants one to two times a week during times of drought or minimal rainfall. Check the soil and, if it is dry, water the plant and wait to water it again until the soil completely dries out. The plant does not require watering if there is rainfall every one to two weeks. Avoid over-watering the Devil's Trumpet as this will kill the plant.
Fertilize the Devil's Trumpet plants once a month with an all-purpose fertilizer. This will provide the plant with the necessary nutrients. Use the fertilizer according to the package directions.
Stake the Devil's Trumpet once it reaches approximately 2 feet in height. This will ensure that it is not knocked over by storms of strong winds.