A gardener can grow Cosmos atrosanguineus, or chocolate cosmos, by planting it in fertile soil in a location with plenty of sunlight, giving it plenty of water, mulching it and pruning it. This is a low-maintenance plant that requires little hands-on involvement and boasts dark burgundy flowers with a rich chocolate scent.
Plant a chocolate cosmos in rich, well-drained soil. If the soil is not fertile enough, add organic compost. Place this plant in a location where it gets plenty of sunlight for the flowers to grow properly.
Fertilize the plant twice with a 5-10-5 ratio fertilizer during the spring and early summer. It requires a 3-inch layer of mulch during the spring and fall once the foliage drops. This keeps the soil moist and the tubers warm during the colder weather of winter.
The plant needs regular water at least once a week, and the soil should remain moist but not excessively wet between watering. It requires more water during the hottest months of the year but should not be overwatered. Remove the faded or dead blossoms on a regular basis to encourage growth. When pruning chocolate cosmos, the flower and at least an inch of the stem need to be removed.