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When to plant cosmos

Start cosmos seeds indoors 4 to 6 weeks before the last frost, plant them out from the last frost to 2 weeks after and sow seed outdoors from the last frost to 2 weeks after.

Your dates for cosmos

Set your ZIP code at the top of the page and we will work out when to plant cosmos where you live, from the frost records of the nearest NOAA weather station. Your ZIP code is remembered on this device only.

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Cosmos planting dates by zone

JFMAMJJASOND Zone 4b Zone 5b Zone 6b Zone 7b Zone 8b Zone 9a
Start indoorsPlant out or sowDates use each zone's typical frost dates. Enter your ZIP code for your own.
Dates from each zone's typical (median) frost dates.
ZoneStart indoorsPlant outSow outdoors
Zone 2aApr 7 to 21May 19 to Jun 2May 19 to Jun 2
Zone 3aMay 28 to Jun 11Jul 9 to 23Jul 9 to 23
Zone 3bMay 18 to Jun 1Jun 29 to Jul 13Jun 29 to Jul 13
Zone 4aMay 8 to 22Jun 19 to Jul 3Jun 19 to Jul 3
Zone 4bMay 1 to 15Jun 12 to 26Jun 12 to 26
Zone 5aApr 26 to May 10Jun 7 to 21Jun 7 to 21
Zone 5bApr 25 to May 9Jun 6 to 20Jun 6 to 20
Zone 6aApr 23 to May 7Jun 4 to 18Jun 4 to 18
Zone 6bApr 18 to May 2May 30 to Jun 13May 30 to Jun 13
Zone 7aApr 12 to 26May 24 to Jun 7May 24 to Jun 7
Zone 7bApr 2 to 16May 14 to 28May 14 to 28
Zone 8aMar 20 to Apr 3May 1 to 15May 1 to 15
Zone 8bMar 10 to 24Apr 21 to May 5Apr 21 to May 5
Zone 9aFeb 23 to Mar 9Apr 6 to 20Apr 6 to 20
Zone 9bFeb 16 to Mar 2Mar 30 to Apr 13Mar 30 to Apr 13

Where frost is rare

Where frost is rare cosmos shifts toward the cooler months: South Florida lists it for planting from fall through spring (September-May), while North Florida plants in spring and early summer. In the Arizona low desert garden cosmos is planted March to June and blooms July to November; around San Antonio a July sowing gives fall color.

ZonePlanting months in Extension guides
Zone 9Mar-Apr and Jun (North Florida); Feb-Mar (Central Florida); Mar-Jun (Arizona low desert); Jul sowing for fall color (San Antonio, TX)
Zone 10Feb-Mar (Central Florida); Jan-May and Sep-Dec (South Florida)
Zone 11Jan-May and Sep-Dec (South Florida)

Based on UF/IFAS Gardening Solutions 'Flowers to Plant in Florida' monthly calendar and UF/IFAS cosmos page; University of Arizona AZ1100 Flower Planting Guide for the Low Desert (Cosmos bipinnatus row); Texas A&M AgriLife Bexar County Timely Tips (July 2011, May 2005). Zone mapping is approximate and ours: UF/IFAS 'North Florida' (north of SR 40) is mostly zones 8b-9a, 'Central' (SR 40-70) about 9b-10a, 'South' (below SR 70) about 10a-11; the Arizona low desert (Phoenix area) is about zone 9b-10a. No UC ANR or Hawaii CTAHR table was found. Warm-winter areas are matched to zones approximately, so use the months for your region.

How to grow cosmosYour full planting calendar

Sources