Purity

Cosmos

75d to harvest

Feathery petals unfurl in a luminous, airy display—Purity cosmos blooms with a crisp, clean whiteness that seems to glow in the garden. The flowers hold their daisy-like form on sturdy, upright stems, with a light, graceful texture that’s especially striking when grown in generous drifts. Grow Purity for abundant, long-lasting cut-flower color and a breezy, romantic presence that keeps the landscape in constant motion.

Crop Dates

Growing note: In frost-free Zone 13a, grow this cool-season crop during the cooler dry season (October–February).

Milestone	Date
Start Indoors	—
Climate	Frost-Free Climate
Transplant / Sow Outdoors	Oct 1st
Harvest Begins	Dec 15th
Harvest Ends	Feb 28th

Crop Details

Trait	Value
Days to Maturity	75
Sun Requirements	Full Sun
Growth Habit	Upright
Support Needed	None
Planting Depth	Normal
Germination Temp (°F)	70
Min Soil Temp (°F)	50
Min Night Temp (°F)	45
Harden Off (days)	7

Frequently Asked Questions

What pest or disease commonly affects Cosmos bipinnatus, and how can I treat it at home?

Cosmos bipinnatus is commonly bothered by aphids, which cluster on tender stems and flower buds and can lead to distorted growth. Spray the plants with a strong jet of water to knock aphids off, then follow with insecticidal soap (especially on the undersides of leaves) and repeat every 5–7 days until new growth is clear. If you see powdery mildew (white, dusty growth on leaves), improve airflow by thinning crowded stems and avoid wetting the foliage; remove the most affected leaves early to slow spread.

How often should I water Cosmos bipinnatus during the main growing phase?

Water Cosmos bipinnatus deeply once the top 1 inch of soil dries out, which is typically about 2–3 times per week in warm weather depending on your soil. Keep the soil evenly moist while plants are establishing, but avoid soggy conditions because Cosmos can develop issues in continuously wet soil. During active flowering, prioritize deep, less-frequent watering rather than daily light sprinkling.

How do I know when Cosmos bipinnatus is ready to harvest?

For cut flowers, harvest when the outer petals are fully open and the center disk is mature (about 75 days from sowing for typical plants). Check daily as blooms open in succession—use a clean cut stem in the morning or evening when flowers are crisp. For seed, let spent flowers dry on the plant until the seed heads turn brown and the seeds feel hard, then harvest and dry them a few more days indoors.