How to grow Garden Cosmos

Cosmos bipinnatus

  • Very rich soil may encourage more foliage than flowers.
  • If plants reach 24 inches to encourage branching by pinching top 3 to 4 inches. 2
  • Tall types may need support. Remove faded flowers to encourage further blooming. 1
  • Does well in well drained soil of average fertility.
  • The plant itself is poisonous

Growing Garden Cosmos from seed

Sow seeds outdoors 1 or in colder climates sow seeds indoors. 2 Will reseed readily.

Try to aim for a seed spacing of at least 0.98 inches (2.5 cm) and sow at a depth of around 0.25 inches (0.64 cm). Soil temperature should be kept higher than 20°C / 68°F to ensure good germination.

By our calculations*, you should look at sowing Garden Cosmos about 28 days before your last frost date .

Transplanting Garden Cosmos

Transplant outdoors after ground has warmed. 2

Ensure that temperatures are mild and all chance of frost has passed before planting out, as Garden Cosmos is a half hardy plant.

Harvesting Garden Cosmos

Put cut flowers in deep water immediately to prevent wilting. 1

Seed Saving Garden Cosmos

Seeds are very easily collected when dry. I simply pick the seeds and scatter them where I want them to grow.

Seed viability is three years.

How long does Garden Cosmos take to grow?

These estimates for how long Garden Cosmos takes to sprout, grow and harvest are from real observations from real gardeners, right around the world.

Days to Germination How long does it take Garden Cosmos to germinate?
7 days

Average 7 days | Min 1 days | Max 21 days (178)

Days to Transplant How long until I can plant out Garden Cosmos?
+ 21 days

Average 21 days | Min 13 days | Max 71 days (9)

Days to Maturity How long until Garden Cosmos is ready for harvest / bloom?
+ 54 days

Average 54 days | Min 32 days | Max 160 days (8)

Total Growing Days How long does it take to grow Garden Cosmos?
= 82 days

When should I plant Garden Cosmos?

Our when to plant Garden Cosmos estimates are relative to your last frost date.

When to sow The number of days to sow Garden Cosmos before or after your last frost date.
28 days before Last Frost Date

Garden Cosmos Etymology

The botanical epithet is from the Latin bipinnatus meaning “staunch” or “like two small wings”.4

Other names for Garden Cosmos

Cosmos

Footnotes

1 “The All-New Illustrated Guide to Gardening” by M. Bradley, T. Cole

2 “New England Gardeners Resource” by J. Heriteau & H.H. Stonehill

3 “Gardening Made Easy

4 Latin Dictionary


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