A favorite! Growing cosmos in your summer gardens adds delicate beauty, especially when planted in informal beds or used in mixed borders. Flowers come in striking reds and oranges or paler crimsons and cream. For arrangements, cut flowers shortly after bloom and place immediately in cold water. Shorter varieties are perfect for containers.
Native to Mexico, cosmos were first discovered by Spanish plant collectors and sent back to Europe in 1799. Cosmos were not introduced to the commercial seed trade until the late 1800’s and did not gain popularity until new early-blooming varieties were developed in the early part of this century.
Be prepared that this half-hardy annual is a giant in the garden, standing 2-5 feet tall.
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Quick Guide: Planting, Growing & Caring for Cosmos
- Flowers come in a huge range of colors, including white, yellow, red, pink and purple
- Be prepared for their height — up to 5 ft. tall, depending on the variety
- Easy to grow in full sun and rich soil
- Good for drier climates
- Sow seed outdoors after last frost or indoors 4-5 weeks before last frost
- Bloom all year; a favorite of beneficial insects
Sunlight: Full sun to partial shade
Maturity: 65-90 days from seed to flower
Height: 24 to 60 inches
Spacing: 12 to 18 inches apart in all directions
Easy to grow, cosmos like rich, fast-draining soil and plenty of sunshine. However, they are hardy and will tolerate most soil conditions and partial shade. Requires moderate water and little attention. Provide protection from the wind, if possible. Excellent for xeriscapes and water-wise gardens.
How to Plant
Sow annuals from flower seeds only. Sow outdoors 1/8 inch deep after last frost or indoors 4-5 weeks before last frost. Seeds will germinate in 3-10 days.
Cosmos plants are not heavy feeders. Too much fertilizer will cause plants to produce excessive leaf growth at the expense of flower production.
Provide support for some of the taller varieties and pinch off the spent blooms to extend the flowering season. Remove plants and discard in fall after the first hard frost.
Tip: Plant cosmos as a border around vegetable gardens to attract beneficial insects, bees and butterflies.
Insect & Disease Problems
Cosmos have few pest problems. However, aphids can appear almost overnight. Watch closely and spray these soft-bodied sucking insects with a strong stream of water to reduce numbers. Apply Safer® Soap if a quick knock-down is required.
- Avoid overhead watering whenever possible (use soaker hoses or drip irrigation)
- Properly space plants to improve air circulation
- Apply organic fungicides to prevent further infection
Seed Saving Instructions
Plants are self-seeding. You can save the seed if you’re interested, but the flowers won’t always come true to type; fancy varieties often revert to the simple single-flower form.
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