Zone 4 planting calendar
Typical frost dates for USDA hardiness zone 4, and a month-by-month table of when to start seeds and plant out. Your own dates depend on your location within the zone, so use these as a starting point.
Zone 4 at a glance
From NOAA 1991–2020 climate normals for 9 example stations in zone 4 (32°F threshold, 50% probability).
Zone 4 is about winter cold, not spring frost
The USDA Plant Hardiness Zone Map divides the country by the average coldest winter night: each zone covers 10°F, and the "a" and "b" halves cover 5°F each. Zone 4 is the right guide for choosing perennials that survive the winter. It is only a rough guide to planting dates, because places with similar winter lows can have very different springs. That is why this page gives a range of frost dates rather than a single date, and why the frost date for your own location is a better input for the seed starting calculator.
Zone 4 gardens typically clear their last spring frost in May and see the first fall frost in late September or early October. That leaves room for tomatoes and peppers from transplants, but choose varieties by days to maturity and start them on time. Cool-season crops go out in April and early May, weeks before warm-season transplants. In this zone a fall frost can arrive while tomatoes are still ripening, so watch the forecast from mid-September.
Typical frost dates in zone 4
The table lists example cities whose airport or city weather station falls in zone 4. "Last frost" is the date after which a 32°F freeze has a 50% chance of still happening; the "1-in-10" column is the date after which there is only a 10% chance. Planting tender crops after the 1-in-10 date is the cautious choice.
| City (station) | Zone | Last frost (median) | Last frost (1-in-10 later) | First fall frost (median) | Freeze-free days |
|---|---|---|---|---|---|
| Caribou, ME | 4a | May 7 | May 24 | Oct 1 | 143 |
| Aberdeen, SD | 4a | May 9 | May 22 | Sep 26 | 139 |
| Minot, ND | 4a | May 10 | May 22 | Oct 1 | 144 |
| Fargo, ND | 4a | May 10 | May 23 | Sep 30 | 143 |
| Duluth, MN | 4b | May 13 | May 29 | Oct 1 | 140 |
| Bismarck, ND | 4a | May 14 | May 27 | Sep 27 | 136 |
| Grand Forks, ND | 4a | May 16 | May 31 | Sep 27 | 133 |
| Great Falls, MT | 4b | May 19 | Jun 2 | Sep 24 | 126 |
| Williston, ND | 4a | May 21 | Jun 3 | Sep 21 | 123 |
Zone shown is the 2023 USDA zone for the ZIP code nearest each weather station, via PRISM data. Frost dates are NOAA 1991–2020 normals for that station. Dates for nearby gardens can differ by a week or more with elevation, slope and distance from water. Find your own station on NOAA's map (see how to find your frost dates).
Month by month: what to start when in zone 4
This table uses the middle example above, Duluth, MN (median last frost May 13), and the University of New Hampshire Extension seed-starting timings. If your last frost is a week later, move everything a week later.
| Month | Start seeds indoors | Plant transplants out | Direct sowing reminders |
|---|---|---|---|
| February | Onions (Feb 4–Feb 18) Parsley (Feb 11–Feb 18) Spinach (Feb 18–Mar 4) | — | — |
| March | Broccoli (Mar 4–Mar 18) Cabbage (Mar 4–Mar 18) Kale (Mar 4–Mar 18) Lettuce (Mar 11–Mar 18) Peppers (Mar 18–Apr 1) Eggplant (Mar 18–Apr 1) Cauliflower (Mar 18–Apr 1) Tomatoes (Mar 25–Apr 8) | — | — |
| April | Basil (Apr 1–Apr 15) Cucumbers (Apr 22–Apr 29) Squash & zucchini (Apr 29–May 6) Melons (Apr 29–May 6) | Spinach (Apr 1–Apr 22) Broccoli (Apr 15–Apr 29) Cabbage (Apr 15) Lettuce (Apr 15–Apr 22) Kale (Apr 15) Onions (Apr 15) Parsley (Apr 22–Apr 29) Cauliflower (Apr 29) | Spinach, lettuce, kale: direct sow once the soil can be worked (see guides) |
| May | — | Tomatoes (May 20–May 27) Cucumbers (May 20–May 27) Peppers (May 27) Eggplant (May 27–Jun 3) Squash & zucchini (May 27) Melons (May 27) Basil (May 27) | Cucumbers, squash: direct sow once soil reaches 70°F, usually after this date Melons: direct sow or transplant once soil is at least 65°F |
Open this schedule in the calculator
Direct-sowing reminders follow the soil-temperature rules in each crop guide (for example, 70°F soil for cucumbers and squash), so the real date depends on your weather. For fall crops, count back from your first fall frost with the fall planting calculator.
Crop guides
Frequently asked questions
When is the last frost in zone 4?
It depends on where you are in the zone. Among the 9 example weather stations on this page, the median last spring freeze (32°F, 1991–2020 NOAA normals) ranges from May 7 to May 21. Look up the station nearest you for a better estimate.
When should I start tomato seeds in zone 4?
For the middle example on this page (last frost May 13, Duluth, MN), the University of New Hampshire Extension timing gives an indoor sowing window of Mar 25–Apr 8 and setting out May 20–May 27. Shift those dates by the difference between your own last frost date and May 13.
Is my hardiness zone the same as my frost date?
No. USDA hardiness zones are based on the average annual extreme minimum winter temperature. They tell you which perennials survive winter, not when spring frosts end, which is why frost dates vary so much within one zone.
Sources
- USDA ARS — Plant Hardiness Zone Map
- PRISM Climate Group, Oregon State University — USDA Plant Hardiness Zone Map data (2023); ZIP lookups via phzmapi.org (not the official USDA map)
- NOAA NCEI — U.S. Climate Normals (1991–2020), incl. interactive map with frost/freeze dates
- University of New Hampshire Extension — Growing Vegetables: When to Plant Your Vegetable Garden
Station data retrieved from NOAA NCEI on 22 Oct 2026. Last reviewed 2026-10-23. Found an error? Tell us.