How to Grow Double Sulphur Cosmos
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Double Sulphur Cosmos
Cosmos sulphureus
flowerDouble Sulphur is a vibrant annual cosmos with fully double, pompom-like golden-yellow flowers that bloom prolifically throughout summer and fall. This compact cultivar grows 2-3 feet tall and produces masses of cheerful blooms on slender stems, making it excellent for cutting and garden display.
When should you plant Double Sulphur Cosmos in your zone?
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Example Double Sulphur Cosmos timeline · Pittsburgh, PA (Zone 6b)
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Plant Double Sulphur Cosmos
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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First Double Sulphur Cosmos blooms
Around Jun 16≈ 60 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Double Sulphur Cosmos dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 2-11; annual in cold climates, can reseed in warmer zones
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Germination & Seedling
7-14 days to germination, 3-4 weeks to transplant-ready sizeTiny seedlings emerge with delicate cotyledons; true leaves begin forming
Keep soil consistently moist but not waterlogged. Provide bright light. Thin seedlings to proper spacing once they have 2-3 true leaves.
Vegetative Growth
3-4 weeksPlant develops bushy foliage with multiple stems; no flowers yet, just feathery green foliage
Pinch back growing tips at 6 inches to encourage branching and bushier growth. Water moderately; ensure good drainage. Light feeding with balanced fertilizer.
Budding
2-3 weeksFlower buds form at stem tips; buds are tight and small, not yet showing color
Continue moderate watering and light fertilizing. Avoid excessive nitrogen which promotes foliage over flowers. Support tall stems if needed.
Flowering
8-12 weeks or until frostFully double, pompom-shaped golden-yellow flowers open and multiply; continuous blooming throughout summer and fall
Deadhead spent flowers regularly to encourage continuous blooming. Water during dry spells. Light weekly feeding with low-nitrogen fertilizer promotes more flowers.
Seed Production & End of Season
Final 2-4 weeks of seasonFlowers fade; if not deadheaded, seed pods develop and mature. Plants decline as frost approaches.
Allow some flowers to go to seed if you want self-seeding next year. Collect seed pods before frost for storage. Remove spent plants after hard freeze.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Spray with water to dislodge; use neem oil or insecticidal soap if severe. Ensure adequate humidity.
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Improve air circulation; apply fungicide such as sulfur or potassium bicarbonate. Avoid overhead watering.
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Use yellow sticky traps; spray with neem oil or insecticidal soap. Remove heavily infested leaves.
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Spray with strong water stream; use insecticidal soap or neem oil. Introduce beneficial insects like ladybugs.
Uses
Ornamental Garnish
CulinaryCosmos flowers are edible and make beautiful, delicate garnishes for salads, desserts, and beverages. Ensure they have not been treated with pesticides. [source]
Cut Flower Arrangements
HouseholdDouble Sulphur cosmos are exceptional cut flowers with long stems and lasting power, perfect for fresh floral arrangements, bouquets, and table decorations. [source]
Pollinator Support
WildlifeThe abundant flowers attract butterflies, bees, and other pollinators throughout the blooming season, making it excellent for pollinator gardens and ecosystem support. [source]
Flower Drying & Pressing
CraftCosmos flowers dry beautifully and retain their color well, making them ideal for dried floral arrangements, pressed flower art, and craft projects. [source]
Traditional Folk Use
MedicinalIn traditional herbalism, cosmos flowers and leaves have been used in herbal teas and preparations, though modern scientific validation is limited. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Cut flowers in early morning when stems are full of moisture. Harvest when blooms are fully open or just beginning to open for longest vase life. Cut above a leaf node to encourage more branching and flowering. Flowers last 7-10 days in a vase with fresh water.
Fun Facts
- 🌱 The name 'cosmos' comes from the Greek word meaning 'order' or 'harmony,' reflecting the flower's perfectly ordered and symmetrical petals.
- 🌱 Double Sulphur cosmos seeds are easy to save and often self-sow the following year, creating a living seed bank in your garden.
- 🌱 Cosmos are extremely heat and drought-tolerant once established, making them ideal for xeriscaping and regions with water restrictions; they actually prefer poor soil and will produce fewer flowers if over-fertilized.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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