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When to plant zinnias in zone 4a

In zone 4a, where the last spring frost typically comes around May 13, start zinnias indoors April 15 to 22 and plant out May 13 to 27.

The zone 4a schedule for zinnias

Start seeds indoors
April 15 to 22
Plant out
May 13 to 27
Sow outdoors
May 13 to 27
Safest planting date (10% frost risk)
May 27

From the median frost dates of the NOAA stations assigned to the 739 ZIP codes in zone 4a, and the timing recommended by Cooperative Extension guides for zinnias.

Frost risk in zone 4a

Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 4a, the typical last frost ranges from about May 6 in the earliest tenth of ZIP codes to May 24 in the latest tenth, and the first fall frost from September 20 to October 3. For a typical place in the zone:

  • April 30Risky: a later frost happens in 9 years out of 10
  • May 13Typical: frost after this date in half of years
  • May 27Safe: 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 4a cities

CityTypical last frostStart indoorsPlant out
Fargo, NDMay 10Jun 5 to 12Jul 3 to 17
Bismarck, NDMay 14Jun 8 to 15Jul 6 to 20
Grand Forks, NDMay 10Apr 12 to 19May 10 to 24

How to grow zinniasAll zonesZinnias in zone 3bZinnias in zone 4bAbout zone 4a

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