Cosmos
Cosmos bipinnatus
Other names: Garden cosmos, Mexican aster
Cosmos is an airy annual with feathery foliage and silky, saucer-shaped flowers in pink, white and crimson. It is one of the easiest flowers to grow from seed, blooms until frost, and performs best in poor soil with little attention.
How to grow cosmos
Light
Full sun. Plants in shade grow tall and lean with few flowers.
Watering
Water seedlings until they are established. Mature plants need watering only in long dry spells.
Soil and feeding
Do not enrich the soil or fertilize. Fertile ground produces tall, leafy plants that flower late.
Planting and pruning
Sow directly outdoors after the last frost and cover the seed with just 1/4 in (6 mm) of soil. Thin to 12 to 18 in (30–45 cm) apart. Pinch the tips at 18 in tall for bushier plants, and deadhead or cut for vases every few days.
Propagation
Grow from seed. Cosmos self-seeds freely, and dry seedheads are easy to collect in fall.
Common problems
- Lots of foliage, few flowers
- Soil is too rich or the site is too shady. Stop feeding and move to full sun next year.
- Plants blow over
- Tall varieties need staking or a sheltered position. Grow them close together so they support one another.
- Powdery white leaves late in the season
- Powdery mildew. Thin plants for air flow.
Questions about cosmos
How long does cosmos take to flower from seed?
About 7 to 10 weeks from sowing.
Does cosmos come back every year?
It is an annual, but it self-seeds so readily that new plants often appear in the same spot the following spring.
Plant details
| Botanical name | Cosmos bipinnatus |
|---|---|
| Family | Asteraceae |
| Native range | Mexico |
| Plant type | Annuals. Annual |
| Soil | Poor to average, well-drained soil |
| Flower color | Pink, white, red |
