PlantSowGrow
How to grow Cosmos (Sensation Mixed)
Cosmos bipinnatus
Airy, feathery plants covered in pink, white and crimson daisies from July until the frosts. Easy and bee-friendly.
At a glance: Sow late April to late May.
When to sow, plant and harvest
Timed for a typical UK garden (last frost mid-April). The app uses your own town's frost dates.
Growing Cosmos (Sensation Mixed): what it needs
- Light
- Full sun · 6+ hours a day
- Watering
- Water in dry spells; pots daily in summer
- Soil
- Any well-drained soil
- Spacing
- 45 cm
- Height
- 1–1.2 m
- In pots
- Grows well in containers
- Feeding
- Liquid feed every two weeks once flowering starts
- Hardiness
- USDA zones 2–11
- Difficulty
- Easy
Step by step
- Late April – late May · 2 weeks after the last spring frost
Sow Seeds Outdoors
Sow thinly where they are to flower, in a sunny spot, into raked, weed-free soil.
- 7–14 days after “Sow Seeds Indoors” · Early May – mid May
Check Germination
Seedlings should appear in 7–14 days. Keep the soil moist. If sown outdoors, thin them to 45 cm apart once they have two true leaves.
- 14–21 days after “Plant Out” · Mid May – late May
Pinch Out Tips (optional)
Pinch out the growing tip above the third or fourth pair of leaves for bushier plants with more flowers.
- 14 days after “Pinch Out Tips” · Early June
Add Support
Push in canes or twiggy sticks and tie in stems before they flop.
- 66–96 days after “Check Germination” · Mid July – early August
First Flowers — Deadhead Regularly
Snip off faded flowers every few days to keep new ones coming for months. Take a photo for your journal!
- Mid October – early November · around the first autumn frost
Clear or Collect Seed
When frost blackens the plants, pull them up for the compost heap. Leave a few seedheads first if you want to save seed.
