Cosmos Growing Guide

Cosmos bipinnatus

Crop Rotation Group

Miscellaneous ●

Soil

Any sunny site with good drainage.

Position

Full sun to partial afternoon shade.

Frost tolerant

Seedlings tolerate light frosts, but plants are killed by freezing temperatures.

Feeding

Mulch the soil with compost prior to planting.

Spacing

Single Plants: 20cm (7") each way (minimum)
Rows: 20cm (7") with 20cm (7") row gap (minimum)

Sow and Plant

Sow cosmos in early spring so the plants can become established before hot weather comes. Cosmos also can be started indoors in containers and set out when the seedlings have at least five leaves, or purchased as bedding plants. Plant seeds in prepared soil about 2 inches (5 cm) apart and one-half inch (1 cm) deep. Thin to 8 inches (20 cm) apart in all directions for dwarf varieties; allow 12 inches (30 cm) between very tall varieties.
Our Garden Planner can produce a personalised calendar of when to sow, plant and harvest for your area.

Notes

Varieties vary greatly in height, colour and flower form. Choose dwarf varieties for tight spaces. Sulphur cosmos (C. sulphureus) thrives in humid heat.

Harvesting

Cosmos make good cut flowers. Pull up the plants and compost them when blooms become few or freezing weather is expected.

Planting and Harvesting Calendar

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Pests which Affect Cosmos

Aphids (General)

Slug

Snail