Garden Cosmos

Garden Cosmos

Cosmos bipinnatus

Plant out 1 week after your last spring frost. Space plants 12 in (30 cm) apart.

Photo: Friedrich Haag, CC BY-SA 4.0 · source

When to plant

Timed from your frost dates, so it holds wherever you garden. Give yours and every step below becomes a date.

See the dates for your garden

Enter your average last spring frost and first fall frost. Every timing on this site turns into a calendar date. Not sure of yours? Your local extension service or a search for “last frost date” and your town will tell you; the app finds them from your location.

Last spring frost
First fall frost

Saved in this browser only. Nothing is sent anywhere.

Optimal Transplant from Nursery

From a plantRecommended from a plant
  1. Plant out1 week after your last spring frost
  2. First harvestabout 45 days after planting out

Optimal Indoor Start

From seedRecommended from seed
  1. Start indoors3 weeks before your last spring frost
  2. Begin hardening offaround your last spring frost
  3. Plant out1 week after your last spring frost
  4. First harvestabout 70 days after sowing

Optimal Transplant

From seed
  1. Plant out1 week after your last spring frost
  2. First harvestabout 70 days after planting out

Optimal Direct Sow

From seed
  1. Sow outdoors1 week after your last spring frost
  2. First harvestabout 70 days after sowing

Growing garden cosmos

Spacing in the row
12 in (30 cm)
Between rows
18 in (46 cm)
Planting depth
1/4 inch
Sun
Full Sun
Soil
Well-drained, average to poor soil.
Germination
7-21 days at 70-75°F
Harvest season
Summer to Fall
Mature height
24-60 inches
Support
Stake tall varieties.
Life cycle
Annual

Sow seeds 1/4 inch deep. Can be direct sown or started indoors for earlier blooms.

Watering. Keep consistently moist until established, then drought tolerant. Avoid overwatering.

Neighbours

The companion chart →

Grows well beside

Feeding

Seedlings
Light liquid fertilizer after true leaves appear.
Growing
Low nitrogen fertilizer if growth is slow; otherwise, optional.
Flowering and fruiting
Phosphorus-rich fertilizer can encourage blooms, but often not needed.
How often
Rarely: sparingly, once or twice during growth if needed; rich soil gives leaves instead of flowers.
Note
Thrives in average soil; excessive fertility reduces flowering and encourages leafy growth.

Your garden cosmos, planned to the day.

Canopy turns these timings into dates from your own frost data, places every plant at its spacing on your garden map, and tracks it all the way to harvest.

Add garden cosmos to your planting calendar →

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