Purity

Family: Asteraceae Annual flowering plant

Planting Schedule

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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.

Light: Full SunMaturity: 75 DaysHabit: Upright

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Purity Planting Dates by USDA Zone

Estimated US hardiness-zone windows for sow, transplant, and harvest. Enter a US ZIP above for exact local dates, or open a zone below.

Zone	Start Indoors	Sow / Transplant	Harvest
Zone 1a	Protected Environment Only
Zone 1b	Protected Environment Only
Zone 2a	Apr 27th	May 25th	Aug 8th – Aug 29th
Zone 2b	Apr 17th	May 15th	Jul 29th – Aug 25th
Zone 3a	Apr 17th	May 15th	Jul 29th – Sep 1st
Zone 3b	Apr 21st	May 19th	Aug 2nd – Sep 21st
Zone 4a	Apr 17th	May 15th	Jul 29th – Sep 24th
Zone 4b	Apr 15th	May 13th	Jul 27th – Sep 27th
Zone 5a	Apr 10th	May 8th	Jul 22nd – Sep 30th
Zone 5b	Apr 6th	May 4th	Jul 18th – Oct 5th
Zone 6a	Apr 3rd	May 1st	Jul 15th – Oct 10th
Zone 6b	Mar 28th	Apr 25th	Jul 9th – Oct 16th
Zone 7a	Mar 23rd	Apr 20th	Jul 4th – Oct 20th
Zone 7b	Mar 13th	Apr 10th	Jun 24th – Oct 28th
Zone 8a	Mar 4th	Apr 1st	Jun 15th – Nov 5th
Zone 8b	Feb 23rd	Mar 23rd	Jun 6th – Nov 12th
Zone 9a	Feb 6th	Mar 6th	May 20th – Nov 26th
Zone 9b	Jan 12th	Feb 9th	Apr 25th – Dec 9th
Zone 10a	—	Oct 1st	Dec 15th – Feb 28th
Zone 10b	—	Oct 1st	Dec 15th – Feb 28th
Zone 11a	—	Oct 1st	Dec 15th – Feb 28th
Zone 11b	—	Oct 1st	Dec 15th – Feb 28th
Zone 12a	—	Oct 1st	Dec 15th – Feb 28th
Zone 12b	—	Oct 1st	Dec 15th – Feb 28th
Zone 13a	—	Oct 1st	Dec 15th – Feb 28th
Zone 13b	—	Oct 1st	Dec 15th – 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.