Native to Mexico, Central and northern South America, this half-hardy annual has naturalized in North America and is considered invasive in some areas. It is a member of the aster family, Asteraceae, that also includes daisy, yarrow, and lettuce. Plants grow up to 7′ tall and have branched four-sided stems that are hairy and carry 12″ long leaves with lance-like divisions. The flowerheads are up to 2.5″ across and consist of yellow ray flowers surrounding yellow disc flowers. Plants often self-seed and seed can be collected in the fall for spring planting. The flowers are attractive to birds and butterflies, especially monarchs. Many cultivars are available that vary most significantly in plant size and flowerhead fullness and color. Suphur cosmos is an excellent choice for a cottage garden and seed can be planted in both spring and mid summer for a continuous bloom into fall. The genus name, Cosmos, comes from the Greek word kosmos, meaning beautiful. The specific epithet, sulphreus, is the Latin word for the sulfur and refers to the flower color of the species.
Type: Half hardy annual
Bloom: Flowerheads up to 2.5″ across with yellow ray and yellow disc flowers in summer
Size: 1-7′ H 2′ W
Light: Full sun; tolerates some shade.
Soil: Average to lean, dry to medium moist, well-drained; over rich soil produces floppy plants.
Hardiness: Half hardy
Care: Deadhead to prolong bloom time; cut back tall lanking plants; srseed in mid summmer to extend color in the garden into fall.
Pests and Diseases: None of significance
Propagation: Sow seed directly in the garden just before the last frost in spring. Alternatively, sow seeds indoors 4-6 weeks before the last frost and plant out spacing 2′ apart after the last frost. Reseed in mid summer. Seeds take 7-21 days to germinate at 75 F and 50-60 days to flower after germination.
Companion Plants: Marigold, canna, crocosmia, cleome
‘Bright Eyes’ (yellow and gold flowerheads; 4′ tall plants)
‘Diablo’ ( intense orange red flowerheads; 30″ tall)
‘Klondyke Mix’ ( yellow to orange and scarlet flowerheads)
‘Ladybird Dwarf Red’, ‘Ladybird Dwarf Gold’, ‘Ladybird Dwarf Orange’, and ‘Ladybird Dwarf Lemon’ (12-16″tall ; early flowering; heat tolerant)
‘Lemon Twist’ (sulfur yellow flowerheads; 30″ tall)
‘Polidor’ (semi-double golden yellow, orange and red flowerheads; 30″ tall)
‘Sunny Gold’ (golden yellow flowerheads; 30″ tall)
‘Sunset’ (double or semi-double red or scarlet orange flowerheads; 35″ tall)
Photo Credit: Shagil Kannur Wikipedia