Plant different varieties from starts or seed for colorful blossoms and fern-like leaves that make cosmos a lovely choice for borders and background.
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
Growing cosmos adds beauty to summer gardens, 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-blossoming varieties were developed in the early part of this century. Half-hardy annual, 2-5 feet tall.
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.
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How to Plant:
Grow annuals from seed 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.
Insects and Disease:
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’s Soap if a quick knock-down is required.
Avoid overhead watering whenever possible
Properly space plants to improve air circulation
Apply organic fungicides to prevent further infection
Seed Saving Instructions:
Cosmos is 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.