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Plant Profile: Chocolate Cosmos (Cosmos atrosanguineus)

cosmos-atrosanguineus-2Chocolate cosmos is a tender perennial native to Mexico where it is extinct in the wild. It is a member of the aster family (Asteraceae) that also includes daisy, yarrow, and lettuce.   Plants grow 2-3′ tall from a fleshy tuber and have pinnately compound dark green leaves with lance-shaped leaflets up to two inches long. The cup-shaped flower heads are carried singly on slender stems that are often tinted red. Each flowerhead consists of six to ten rich chocolate maroon ray flowers around a mass of dark disc flowers. They have a vanilla chocolate fragrance and are one to 1 ¾” wide. Flowers appear from mid-summer to fall and deadheading prolongs bloom time. Since the tubers are tender they are best lifted in the fall and stored indoors over the winter. Rich soil results in vegetative growth at the expense of flowers. Flowers are good in the vase. The genus name name, Cosmos, comes from the Greek kosmos meaning beautiful. The specific epithet, atrosanguineus, comes from Latin atro- meaning dark plus sanguis meaning blood and refers to the color of the flowers.

Type: Tender perennial

Bloom: Chocolate maroon daisy-like flowers from mid-summer to fall

Size: 2-3’ H x 1-2’ W

Light: Full sun

Soil: Average, moist, well-drained

Hardiness: Zones 7-10

Care: Deadhead to prolong bloom; lift tubers and store indoors during the winter.

Pests and Diseases: Stem canker, powdery mildew, Rhizoctonia stem rot, gray mold, and aphids

Propagation: Basal cuttings with bottom heat

Companion plants: Coneflower, Black eyed susan, zinnia, tall verbena, coleus “Rustic Orange’, Mexican feather grass, crocosmia, golden marguerite, tickseed (Coreopsis), Shasta daisy ‘Becky’