Radiance, Cosmo Seeds

Radiance Cosmos Seed

Award-winning rose petals encircle dramatic crimson eyes
Historic selection won national honors in 1948
Airy stems flower generously through summer
Excellent for beds, pollinators, and cutting

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Key Attributes

Botanical Name

Cosmos bipinnatus

Days to maturity

90 Days

Sun

Full Sun

Packet

500 Seeds

About Radiance, Cosmos Seed, Cosmos Seed

The Radiance Cosmo is a radiant flower variety that produces very stunning rose-colored petals that have a deep crimson eye. This popular variety was the All America Selections winner in 1948. Radiance is a suitable for cutting, beds and borders, and the pollinator garden.

Growing details

Planting

Sow Depth

1/8"

Days to Germination

7–14 days

Germination Type

A - No Pretreatment

In-row plant spacing

12-18"

Plant profile

Life Cycle

Annual

Plant Height

48 inches

Growth Habits

Upright

Seed & variety

Seeds Per Ounce

4,500

Color

Pink, Red

Seed Type

Open Pollinated

Before Planting

Cosmos flowers freely in full sun and ordinary, fast-draining soil. Remove established weeds and loosen the surface, but skip rich amendments that encourage tall leafy plants. Rake a fine seedbed; fresh seed normally needs no pretreatment.

Planting

Start cosmos indoors 4–10 weeks before the last spring frost, or direct sow after frost where the season is long. Keep the medium warm and evenly moist until emergence, then provide strong light and airflow. Harden seedlings gradually before transplanting into warm soil. Space compact cosmos about 9 inches apart and tall branching types 12–18 inches apart.

Watering

Once established, cosmos prefers deep, infrequent watering. Let the surface dry between irrigations, supply extra moisture during extended heat, and avoid keeping the crown continuously wet.

Fertilizer

Feed cosmos lightly after establishment with a balanced fertilizer. Repeat only if flowering or growth weakens; rich nitrogen feeding causes soft stems and delayed blooms.

Harvesting

Cosmos flowers are ready when stems are firm and blooms show mature color without fading. Cut during cool, dry conditions; for seed, leave selected heads until brown and dry.

Tips

Pinch young cosmos where branching is desired and provide discreet support before flowering. Remove faded blooms to extend display, or retain selected heads for seed and winter interest.

Pests & Diseases

Cosmos can develop powdery mildew, Botrytis, Phomopsis stem canker, and white smut. A sunken stem lesion can girdle an otherwise healthy plant, so remove affected stems promptly. Lean soil and wider spacing keep plants sturdier; avoid carrying diseased stems into saved-seed or dried-flower material.

Cosmos can attract aphids, thrips, spider mites, Japanese beetles, and slugs. Scout flowers and new growth regularly, handpick when practical, and protect beneficial insects with targeted controls.