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When to plant zinnias in zone 5b

In zone 5b, where the last spring frost typically comes around May 1, start zinnias indoors May 18 to 25 and plant out June 15 to 29.

The zone 5b schedule for zinnias

Start seeds indoors
May 18 to 25
Plant out
June 15 to 29
Sow outdoors
June 15 to 29
Soil warm enough (70°F), about
June 15

From the median frost dates of the NOAA stations assigned to the 2,546 ZIP codes in zone 5b, and the timing recommended by Cooperative Extension guides for zinnias.

Frost risk in zone 5b

Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 5b, the typical last frost ranges from about April 21 in the earliest tenth of ZIP codes to May 18 in the latest tenth, and the first fall frost from September 30 to October 19. For a typical place in the zone:

  • April 18Risky: a later frost happens in 9 years out of 10
  • May 1Typical: frost after this date in half of years
  • May 16Safe: a later frost only 1 year in 10

Zinnias are killed by frost, so if you want to be safe, plant out after the safe date rather than the typical one, or be ready to cover plants on a cold night.

Your dates for zinnias

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

Enter your ZIP code

Zinnias in zone 5b cities

CityTypical last frostStart indoorsPlant out
Milwaukee, WIApr 19May 26 to Jun 2Jun 23 to Jul 7
Madison, WIMay 1May 26 to Jun 2Jun 23 to Jul 7
Des Moines, IAApr 18May 10 to 17Jun 7 to 21
Aurora, ILApr 19May 17 to 24Jun 14 to 28
Fort Collins, COMay 2May 29 to Jun 5Jun 26 to Jul 10
Naperville, ILApr 19May 17 to 24Jun 14 to 28
Rockford, ILApr 24May 17 to 24Jun 14 to 28
Elgin, ILApr 26May 21 to 28Jun 18 to Jul 2
Greeley, COMay 2May 20 to 27Jun 17 to Jul 1
Green Bay, WIApr 30Jun 6 to 13Jul 4 to 18
Davenport, IAApr 19May 14 to 21Jun 11 to 25
Longmont, COMay 6May 31 to Jun 7Jun 28 to Jul 12

How to grow zinniasAll zonesZinnias in zone 5aZinnias in zone 6aAbout zone 5b

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