Zone 4b Frost Dates and Planting Schedule

In USDA zone 4b, the typical last frost is May 10 and the typical first frost is September 30: the medians across its 787 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 30

range Sep 14 to Oct 8

Typical last spring frost

May 10

range May 2 to Jun 2

Median and 10th to 90th percentile across 787 ZIP codes in zone 4b, from each ZIP code's nearest NOAA station (1991–2020 normals). The spread is 31 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 4b 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 4b Planting Schedule

Typical for zone 4b, counted from the zone's typical May 10 last frost and Sep 30 first frost with the Season Planner's crop timing. Enter your ZIP code for your exact dates.

Typical for zone 4b

Mar 15–Mar 29 Start tomatoes indoors

Tomato seed needs 6 to 8 weeks under lights before it goes out.
Mar 29–Apr 12 Sow peas outdoors

Peas take cold soil and light frost in stride.
Apr 12–Apr 26 Sow leaf lettuce outdoors

Sow again every 2 to 3 weeks for a steady supply.
May 17–May 24 Transplant tomatoes and peppers

Once nights stay above 50°F.
May 17–May 24 Sow bush beans

Beans rot in cold soil: wait for 60°F at 4 inches deep.
Jul 8–Jul 22 Sow a fall crop

Kale, carrots, spinach or lettuce, 10 to 12 weeks before the first fall frost.
Oct 7–Oct 14 Plant garlic

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

Zone 4b Cities and Their Frost Dates

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

Rochester, MN:last frost Apr 30, first Oct 6
Eau Claire, WI:last frost May 8, first Oct 4
Great Falls, MT:last frost May 19, first Sep 24
Saint Cloud, MN:last frost May 7, first Sep 30
Winona, MN:last frost Apr 21, first Oct 19
Golden, CO:last frost May 5, first Oct 5
Conifer, CO:last frost May 23, first Sep 22
Canaan, VT:last frost May 31, first Sep 21

Zone 4b Frost FAQ

When is the last frost in zone 4b?

Typically around May 10, but it ranges from May 2 to June 2 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 4b?

Typically around September 30, ranging September 14 to October 8 across zone 4b.

When do you plant tomatoes in zone 4b?

Typically May 17 to May 24, 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 4b covers ZIP codes in Colorado, Maine, Minnesota, Montana, New Hampshire, South Dakota, Vermont, Wisconsin, Wyoming.

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

Free book · 23 pages, PDF

The Spacing & Planting Cheat Sheet

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