How to grow Cosmos in the UK
Cosmos bipinnatus
Cosmos (Cosmos bipinnatus) is a flower that grows well in UK gardens. Flowers from July to first frost. Pinch out tips when 30cm high for bushier plants. This guide covers when and how to sow Cosmos, the soil and position it likes, watering and feeding, companion planting, and when to harvest.
When to sow & grow Cosmos
Sowing and harvest window through the year (UK):
Jan | Feb | Mar | Apr Sow | May Plant | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
Soil, position & care
- Soil
- Any reasonable, moisture-retentive but free-draining soil
- Soil pH
- 6.0–7.5
- Position
- Full sun for most; some tolerate light shade
- Sowing depth
- Surface to 1 cm (check light requirement)
- Spacing
- 15–30 cm apart
- Sowing
- Sow under cover late winter–spring, or direct after the last frost
- Growing
- Water regularly; pinch tips for bushier plants
- Harvest & upkeep
- Deadhead often to prolong flowering
- Watch for
- Slugs and snails on seedlings; aphids on soft growth
Companion planting for Cosmos
No specific companion notes for this plant.
Add Cosmos to your free 12-month plan and get watering & sowing reminders — no sign-up needed.
Cosmos FAQs
When should I sow Cosmos in the UK?
In the UK, sow Cosmos in April. Sowing across these months gives the plant the right soil temperature and day length to establish well.
How much sun does Cosmos need?
Cosmos prefers full sun (6+ hrs direct).
Is Cosmos easy to grow?
Easy — good for beginners. Flowers from July to first frost. Pinch out tips when 30cm high for bushier plants.