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When to plant tomatoes in zone 4a

In zone 4a, where the last spring frost typically comes around May 13, start tomatoes indoors April 7 to 21 and plant out June 2 to 16.

The zone 4a schedule for tomatoes

Start seeds indoors
April 7 to 21
Plant out
June 2 to 16
Soil warm enough (60°F), about
June 2
First harvest, roughly
July 24 to September 14

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 tomatoes.

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

Tomatoes 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 tomatoes

Set your ZIP code at the top of the page and we will work out when to plant tomatoes 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

Tomatoes in zone 4a cities

CityTypical last frostStart indoorsPlant out
Fargo, NDMay 10Mar 30 to Apr 13May 25 to Jun 8
Bismarck, NDMay 14Apr 2 to 16May 28 to Jun 11
Grand Forks, NDMay 10Apr 3 to 17May 29 to Jun 12

How to grow tomatoesAll zonesTomatoes in zone 3bTomatoes in zone 4bAbout zone 4a

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