Garden Cosmos (Cosmos bipinnatus)

How much light does a Garden Cosmos need?

Full sun is the preferred light for garden cosmos, meaning 6 or more hours of direct sunlight a day. The plant also tolerates part shade, described as direct sunlight for only part of the day, roughly 2 to 6 hours. The two light settings listed for this plant are full sun and part shade, with full sun preferred.

• Light: Full sun and part shade (full sun preferred)^1,1,2,3

How often to water a Garden Cosmos

The listed water range for garden cosmos runs from dry to medium. One source says it tolerates dry, porous soils. Its soil drainage is listed as well drained and occasionally dry. Medium moisture sits at the upper end of the range, and dry sits at the lower end. Well drained soil and a water range from dry to medium are the two moisture facts on record.

• Water: Dry to medium³

Best soil for a Garden Cosmos

This plant is listed for soil that is well drained and occasionally dry. One source describes it as tolerating dry, porous soils. Its water range runs from dry to medium. Drainage is the main soil detail recorded for garden cosmos. Good drainage is the first trait listed, and occasionally dry soil is the second. No cited source records a preferred soil pH, so that value is not documented here. Well drained soil and dry, porous soil are the two soil conditions on record.

• Soil drainage: Well drained and occasionally dry^1,1,4,3
• Soil pH: pH 6–9^1,1

Hardiness and temperature

USDA hardiness zones 2a through 11b are listed for garden cosmos. The listing names every half-zone from 2a to 11b. Its plant type is annual, and its listed growth rate is rapid. Its native range is recorded with the region codes MXC, MXE, MXG, MXN and MXS. In the lower 48 US states, its native status is introduced.

• Hardiness: Zones 2a–11b¹

Pruning a Garden Cosmos

Deadheading is the pruning method listed for garden cosmos. One source states that deadheading will promote further blooms. Another source advises deadheading to encourage continuous flowering. No other pruning type is listed for this plant. Its flowers come in white, pink, purple, yellow and red.

• Pruning: Deadheading^1,5,6

How to plant a Garden Cosmos

Plant garden cosmos where your zone falls between 2a and 11b. Allow 2–3 ft (0.6–0.91 m) of room for each plant's mature spread. Expect a mature height of 2–4 ft (0.61–1.22 m). Choose a site with full sun, which it prefers, or with part shade. Seed can be sown directly in the garden. Pick a well drained spot.

• Hardiness: Zones 2a–11b¹

Winter care

Annual is the plant type listed for garden cosmos. Its hardiness listing covers zones 2a through 11b in half-zone steps. Seed is the propagation method listed for it. Its mature height is 2–4 ft (0.61–1.22 m). Its listed growth rate is rapid. Pruning is limited to deadheading, which will promote further blooms.

• Hardiness: Zones 2a–11b¹

How to propagate a Garden Cosmos

Seed is how garden cosmos is propagated. One source states that the propagation of cosmos is primarily accomplished by seed, which can be directly sown in the garden. Seed is the only propagation method listed for this plant. Its plant type is annual. Its listed bloom colors are white, pink, purple, yellow and red.

• Propagation: Seed^1,3

Common problems

Aphids, aster leafhopper, gray looper moth, thrips, true bugs and Japanese beetles are the pests listed for garden cosmos. The diseases listed are stem canker, powdery mildew, gray mold, aster yellows, viruses, white mold, bacterial wilt and leaf spots. In all, six pests and eight diseases are listed for this plant.

• Common pests: aphids, aster leafhopper, gray looper moth, thrips, true bugs and japanese beetles^1,7,3,7
• Common diseases: stem canker, powdery mildew, gray mold, aster yellows, viruses, white mold, bacterial wilt and leaf spots^1,7,7,3

Questions and answers

How much sun does garden cosmos need?

Full sun is preferred, meaning at least 6 hours of direct light each day. Part shade is also listed, at about 2 to 6 hours of direct sun.

Can you grow garden cosmos from seed?

Seed is the listed propagation method, and it can be sown directly in the garden. No other method is listed for this plant. It is also listed as an annual with a rapid growth rate.

How big does garden cosmos get?

Garden cosmos reaches 2–4 ft (0.61–1.22 m) tall at maturity. Its spread is 2–3 ft (0.6–0.91 m). Its blooms come in white, pink, purple, yellow and red.