Seed Depth: ¼ inch

Seed Spacing: 12–18 inches

Row Spacing: 24–36 inches

Sunlight: Full sun

Days to Sprout: 7–14 days

Days to Bloom: 75–90 days

Plant Height: 36–48 inches

Plant Type: Annual

Sunlight: Requires full sun for optimal growth, with at least 6–8 hours of daily light.

Soil Type: Performs best in well-drained, average to poor soil. Avoid overly rich soil to prevent excessive foliage growth at the expense of blooms.

When to Plant: Direct sow after the last frost, or start indoors 4–6 weeks early and transplant once soil has warmed.

Direct Sowing: Sow seeds ¼ inch deep in prepared soil. Thin seedlings to 12–18 inches apart once established.

Indoor Sowing: Start in seed trays with light, well-draining mix. Keep warm and lightly moist until germination, then transplant after hardening off.

Succession Planting: Not typically needed—plants bloom continuously through the summer and fall until frost.

Watering: Water moderately during dry spells. Established plants are drought-tolerant and prefer slightly dry soil over soggy conditions.

Fertilizing: Avoid heavy feeding. Too much fertilizer can lead to more foliage and fewer blooms. A light application of compost at planting is often sufficient.

Mulching: Apply mulch around the base to retain soil moisture and reduce weed pressure, especially during hot summer months.

Staking: Support may be needed in windy areas due to the plant’s tall, delicate stems.

Deadheading: Regularly remove spent blooms to encourage continuous flowering through the season.

Harvesting Fresh Flowers: Cut cosmos blooms early in the morning, just as the petals begin to unfurl. Use clean scissors or snips and place immediately in cool water. Regular harvesting encourages continuous blooming throughout the season.

When to Harvest Seeds: Leave some flowers on the plant to fully mature. Seed heads are ready when the petals drop and the centers dry to a crisp brown.

How to Collect: Snip off dried flower heads and gently pull them apart to release the long, dark, spindle-shaped seeds.

Drying and Cleaning: Spread seeds on a paper towel or screen in a cool, dry place for several days. Remove any remaining chaff or plant debris.

Storage Tips: Store completely dry seeds in a labeled envelope or airtight container. Keep in a cool, dark, and dry place. Cosmos seeds can remain viable for 3–4 years.