Zone 4a Frost Dates and Planting Schedule

In USDA zone 4a, the typical last frost is May 11 and the typical first frost is September 28: the medians across its 926 ZIP codes, from NOAA 1991–2020 normals at the station nearest each one.

By HarvestMath Editors October 1, 2026 Share:

Typical first fall frost

Sep 28

range Sep 20 to Oct 9

Typical last spring frost

May 11

range May 3 to May 23

Median and 10th to 90th percentile across 926 ZIP codes in zone 4a, from each ZIP code's nearest NOAA station (1991–2020 normals). The spread is 20 days in spring.

A hardiness zone is a winter-cold rating: the average coldest night of the year. It doesn't predict when frost ends in spring. Two ZIP codes in zone 4a can be weeks apart on their last frost, so the dates here are a typical range, not your date.

Your exact frost dates

Find your dates by

US ZIP code

Enter a ZIP code or pick your hardiness zone to see your frost dates.

Zone 4a Planting Schedule

Typical for zone 4a, counted from the zone's typical May 11 last frost and Sep 28 first frost with the Season Planner's crop timing. Enter your ZIP code for your exact dates.

Typical for zone 4a

Mar 16–Mar 30 Start tomatoes indoors

Tomato seed needs 6 to 8 weeks under lights before it goes out.
Mar 30–Apr 13 Sow peas outdoors

Peas take cold soil and light frost in stride.
Apr 13–Apr 27 Sow leaf lettuce outdoors

Sow again every 2 to 3 weeks for a steady supply.
May 18–May 25 Transplant tomatoes and peppers

Once nights stay above 50°F.
May 18–May 25 Sow bush beans

Beans rot in cold soil: wait for 60°F at 4 inches deep.
Jul 6–Jul 20 Sow a fall crop

Kale, carrots, spinach or lettuce, 10 to 12 weeks before the first fall frost.
Oct 5–Oct 12 Plant garlic

Cloves go in 1 to 2 weeks after the first killing frost, for next summer.

Zone 4a Cities and Their Frost Dates

Same zone, different dates: each city's own station.

Fargo, ND:last frost May 10, first Sep 30
Bismarck, ND:last frost May 14, first Sep 27
Brainerd, MN:last frost May 13, first Sep 27
New England, ND:last frost May 16, first Sep 24
Auburn, NY:last frost May 2, first Oct 18
Crosby, MN:last frost May 13, first Sep 27
Dickinson, ND:last frost May 18, first Sep 25
Buena Vista, CO:last frost May 27, first Sep 23

Zone 4a Frost FAQ

When is the last frost in zone 4a?

Typically around May 11, but it ranges from May 3 to May 23 across the zone's ZIP codes (10th to 90th percentile). Enter your ZIP code for your own station's date.

When is the first frost in zone 4a?

Typically around September 28, ranging September 20 to October 9 across zone 4a.

When do you plant tomatoes in zone 4a?

Typically May 18 to May 25, a week or two after the zone's typical last frost. Your own last frost can be weeks either side of that.

Neighboring Zones

Zone 4a covers ZIP codes in Colorado, Maine, Minnesota, Montana, North Dakota, New York, South Dakota, Wisconsin.

A garden in a zone 4a climate — An illustration of a zone 4a garden.

Free book · 23 pages, PDF

The Spacing & Planting Cheat Sheet

When to start, when to plant, how far apart.