Cosmos — Growing reference
| Scientific name | Cosmos bipinnatus |
|---|---|
| Seed germination (days) | 3–7 |
| Soil temperature for germination (°C) | 18.3–23.9 |
| First harvest or flowering (days) | 60–90 |
| Measured from | Seed |
| Plant spacing (cm) | 22.9–45.7 |
| Mature height (cm) | 61–152.4 |
| Mature spread (cm) | 30.5–61 |
| USDA hardiness zones | 2–11 |
| Light | Full sun |
| Water | Low |
| Sowing method | Direct sow |
Growing directions
Direct sow after last frost (or start indoors 3–4 weeks before) in well-drained, poor to average, neutral soil in full sun; cosmos blooms most prolifically in lean, dry soil — rich, moist conditions produce excessive foliage at the expense of flowers. Cosmos bipinnatus is one of the most beloved, easy-to-grow garden annuals, producing feathery, thread-fine leaves on branching stems and a long succession of daisy-like flowers 2–4 inches across in white, pink, rose, burgundy, and bicolors from early summer through frost; individual plants bloom for 3–4 months when kept deadheaded. It is a superb butterfly plant, beloved by monarchs, swallowtails, and skippers, and a major nectar source for bumblebees and honeybees; it self-seeds freely in disturbed soil. Minimal care required — simply thin to 9–18 inches and let it bloom.
Source and local conditions
Typical planning ranges from OpenPlantDB (CC0). Cultivar, climate, season and growing method can change these values. Confirm the seed label and local guidance before planting.
OpenPlantDB · cosmos-bipinnatus
Source & verification
OpenPlantDB · CC0