USDA Zone 4a
Zone 4 · The Upper Midwest
Average annual extreme minimum temperature: -30 to -25 °F (-34.4°C to -31.7°C).
The heart of Minnesota and North Dakota, south-central Alaska, and the cold uplands of northern New England and New York — −30 to −20°F winters and a season that runs roughly mid-May to early October.
By the numbers
- Median last frost
- May 13
- Median first frost
- September 28
- Median season
- 138 days
- ZIPs tracked
- 772
Medians across every ZIP we track in zone 4a, derived from NOAA 1991–2020 climate normals. Look up your own ZIP for local dates — within a zone, frost varies by weeks.
Where you'll find zone 4
Most of North Dakota (three-quarters of its ZIPs in our data are 4a) and the broad middle of Minnesota, plus south-central Alaska — Anchorage neighborhoods run 4b, Soldotna 4a — and pockets of the northern Great Lakes, Adirondacks, and northern New England. Northwest and northeast Iowa keep small 4b corners.
Vegetables that earn their keep
- Cool-season, frost-tolerant: asparagus, beets, broccoli, cabbage, spinach (Cornell: "best in cool weather and tolerates frost")
- Warm-season, planted after the last frost (~May 20 upstate NY): beans, sweet corn, eggplant, peppers, tomatoes
- Succession crops: lettuce and radish, sown in repeated short rows
- NDSU's northern variety picks (see zone 3) apply across this band
Fruits & perennials that overwinter
- All UMN zone-3 apples, plus Triumph® — "very good in Zone 4, not recommended for Zone 3"
- Raspberries 'Killarney' and 'Encore' (hardy to zone 4); fall-bearing 'Polana', 'Joan J', 'Anne' are zone-4-only (NDSU)
- Purple raspberry 'Amethyst' — hardiest of the purples
- Tart cherries, juneberries, honeyberries — all carry colder ratings and are easy here
The May 20 rhythm
Cornell's upstate planting schedule — built around a last spring frost near May 20 and a first fall frost around October 1 — is the template for the whole band. Cool-season crops go in from April; everything frost-tender waits for late May; and the schedule shifts a week or ten days in either direction for warmer or cooler corners of the zone.
Two-list gardening
Cornell's division is the useful one: crops that tolerate frost (beets, broccoli, cabbage, spinach, peas) versus crops that frost kills (beans, corn, eggplant, peppers, tomatoes). The first list owns April, May, and September; the second list owns the hundred-some days in between. Plant accordingly and the zone feels twice as long.
Fruit gets easier
Zone 4 keeps every zone-3 apple and adds UMN's Triumph®; fall-bearing raspberries (Polana, Joan J, Anne) become an option that zone 3 can't risk. Winter protection drops from mandatory to prudent: tree guards on young trunks, snow cover or cane burial on brambles in exposed sites.
The toolkit still pays
UMN's season-extension numbers (black plastic +5°F soil, clear +14°F, row covers to ~20°F, water-filled protectors worth three weeks on tomatoes) were written for zones 3–4. Here they're less about making the season possible and more about making it comfortable — earlier tomatoes, later greens, insurance against the late frost that visits every few Mays.
Plant guides, timed to your frost dates
Every guide gives its planting calendar relative to your last frost — the dates above (or your ZIP's) drop straight in.