Cosmos: Sow and Grow GuideUpdated 14 days ago
Cosmos are easy-to-grow, vibrant flowers that add color and attract pollinators to your garden. Here's a concise guide to successfully sowing and growing cosmos.
When to Sow
Sow cosmos seeds outdoors after the last frost when the soil has warmed to at least 60°F. For an earlier start, seeds can be sown indoors 4-6 weeks before the last frost and transplanted once the weather is consistently warm.
Outdoor Sowing
Choose a sunny location with well-drained soil. Sow seeds 1/4 inch deep and 12-18 inches apart, depending on the variety. Cosmos prefer poor to average soil, as overly rich soil can lead to fewer blooms. Water gently after sowing and keep the soil moist until germination, which typically takes 7-10 days.
Indoor Sowing
For indoor sowing, plant seeds 1/4 inch deep in seed trays filled with a light, well-draining soil mix. Keep the soil moist and place the trays in a warm, sunny spot or under grow lights. Transplant seedlings outdoors once they have several sets of true leaves and the danger of frost has passed.
Care and Maintenance
Cosmos thrive in full sun and are drought-tolerant once established. Water regularly, but be careful not to overwater. Deadhead spent flowers to encourage continuous blooming throughout the season. Cosmos generally do not require fertilization, but if necessary, a light application of a balanced fertilizer can be used sparingly.
Pests and Diseases
Cosmos are relatively pest-resistant but can occasionally attract aphids and spider mites. These can be managed with insecticidal soap or by introducing natural predators like ladybugs. Cosmos are also generally disease-resistant, but good air circulation and avoiding overhead watering can prevent fungal issues.
Harvesting
Cosmos make excellent cut flowers. Harvest blooms when the petals have fully opened by cutting the stems in the morning. Regularly cutting flowers will promote more blooms throughout the season.
Garden Use
Cosmos are ideal for borders, wildflower gardens, and pollinator gardens. Their tall, airy growth habit makes them great for adding height and movement to garden beds. Cosmos also attract beneficial insects, making them valuable companions for vegetables and other flowering plants.
For further details, visit the full guide on the Botanical Interests Blog.