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When to plant zinnias in zone 4b

In zone 4b, where the last spring frost typically comes around May 8, start zinnias indoors June 2 to 9 and plant out June 30 to July 14.

The zone 4b schedule for zinnias

Start seeds indoors
June 2 to 9
Plant out
June 30 to July 14
Sow outdoors
June 30 to July 14
Soil warm enough (70°F), about
June 30

From the median frost dates of the NOAA stations assigned to the 1,164 ZIP codes in zone 4b, and the timing recommended by Cooperative Extension guides for zinnias.

Frost risk in zone 4b

Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 4b, the typical last frost ranges from about May 1 in the earliest tenth of ZIP codes to May 25 in the latest tenth, and the first fall frost from September 22 to October 8. For a typical place in the zone:

  • April 26Risky: a later frost happens in 9 years out of 10
  • May 8Typical: frost after this date in half of years
  • May 22Safe: 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 4b cities

CityTypical last frostStart indoorsPlant out
Rochester, MNApr 30May 30 to Jun 6Jun 27 to Jul 11
Duluth, MNMay 6Apr 8 to 15May 6 to 20
Lakeville, MNMay 2May 30 to Jun 6Jun 27 to Jul 11
St. Cloud, MNMay 7Jun 8 to 15Jul 6 to 20
Eau Claire, WIMay 8May 31 to Jun 7Jun 28 to Jul 12
Great Falls, MTMay 19Jun 28 to Jul 5Jul 26 to Aug 9

How to grow zinniasAll zonesZinnias in zone 4aZinnias in zone 5aAbout zone 4b

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