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TableEntry 32Reviewed 2026-10-16

USDA zone 5

Zone 5 tells you how cold winter usually gets: an average yearly low of −20 to −10°F. It does not tell you when your last frost comes. Six zone 5 cities show how far apart frost dates and season lengths can be inside one zone, using NOAA's 1991–2020 normals, USDA's 2023 map and extension guides.

What zone 5 means

USDA's Plant Hardiness Zone Map is based on the average annual extreme minimum winter temperature, shown in 10°F zones and 5°F half zones (USDA ARS). The map legend gives zone 5 as:

Half zoneAverage annual extreme minimum (°F)(°C)
5a−20 to −15−28.9 to −26.1
5b−15 to −10−26.1 to −23.3

Where it is, in the sources' own words: "Nearly all of Iowa is now in Zone 5, with the northern half in 5a and the southern half in 5b," with small areas of 4b in northeast Iowa and 6a in the southeast and southwest (Iowa State, December 2023). Illinois runs from "zone 5a in northwestern Illinois," and the state's 5b/6a boundary moved about 60 miles north on the 2023 map, from around Springfield to around Peoria (Illinois Extension, January 2024). For any other place, look up the ZIP code on USDA's map; the six cities below were checked that way in October 2026.

Zone 5 does not set your frost dates

A zone number is a winter-cold statistic. As University of Idaho Extension puts it, "Knowing your hardiness zone will not tell you how many frost-free days you will have." Frost dates and season length come from a different data set: NOAA's Climate Normals, which give the dates of the last spring and first fall 32°F freeze at stated probabilities and the length of the growing season. The hardiness zones guide explains the difference in detail.

Six zone 5 cities, side by side

Zone: USDA ARS ZIP search for the city ZIP shown (2023 map, with the 2012 zone in brackets). Frost data: NOAA NCEI 1991–2020 normals for the weather station at or near each city, 32°F threshold. The 50% date is the median; a 10% spring date means a later freeze about 1 year in 10, and a 10% fall date means a freeze that early about 1 year in 10 (NC State's guide to these tables).

Place (ZIP)Zone 2023 (2012)Last spring freeze 50% (10%)First fall freeze 50% (10%)Season, days 50% (90%)
Minneapolis, MN (55401)5a (4b)Apr 23 (May 7)Oct 18 (Oct 1)176 (158)
Des Moines, IA (50309)5b (5b)Apr 18 (May 2)Oct 20 (Oct 4)184 (165)
Burlington, VT (05401)5b (5a)Apr 29 (May 11)Oct 15 (Oct 2)169 (149)
Madison, WI (53703)5b (5a)May 1 (May 16)Oct 10 (Sep 26)160 (140)
Fort Collins, CO (80521)5b (5b)May 2 (May 14)Oct 7 (Sep 24)157 (139)
Concord, NH (03301)5b (5b)May 8 (May 22)Oct 3 (Sep 21)146 (128)

Stations: Minneapolis/St Paul AP, Des Moines Intl AP, Burlington Intl AP, Madison Dane Rgnl AP, Ft Collins, Concord Muni AP. NCEI's season length is its own statistic, so it can differ by a day or two from the gap between the two median dates. For season length, NC State calls the 90% value the conservative one: a season at least that long in about 9 years out of 10.

What the table shows:

Frost-free season at six USDA zone 5 places, NOAA 1991–2020 normalsA March to November timeline with one row per place: Minneapolis (zone 5a), Des Moines, Burlington, Madison, Fort Collins and Concord (all zone 5b). Each green bar runs from the 50 percent date of the last spring 32 degree freeze to the 50 percent date of the first fall freeze, with the season length in days at the right. Short red ticks mark the 10 percent dates: a later spring freeze or an earlier fall freeze happens about one year in ten. The bars differ by up to 38 days although all six places are in zone 5. Four numbered markers match the list below the drawing. Median frost-free season (32°F), NOAA NCEI normals 1991–2020 Mar Apr May Jun Jul Aug Sep Oct Nov Minneapolis, MN 5a 176 days Des Moines, IA 5b 184 days Burlington, VT 5b 169 days Madison, WI 5b 160 days Fort Collins, CO 5b 157 days Concord, NH 5b 146 days 50% last spring to 50% first fall freeze 10% dates 1 2 3 4
Drawing by The More One Sows, based on the cited sources. Dates as in the table above. Not to scale vertically; the time axis is to scale.
  • 1. Half zone from USDA's ZIP search (2023 map): only Minneapolis is 5a, the others 5b
  • 2. Green bar: from the 50% last spring 32°F freeze to the 50% first fall freeze (NOAA NCEI 1991–2020); NOAA's median season length in days
  • 3. Red ticks: 10% dates, when a later spring or earlier fall freeze happens about 1 year in 10
  • 4. Season lengths range from 184 days (Des Moines) to 146 (Concord) inside the same zone

Same city, different data sets

Iowa State Extension publishes county frost and freeze tables from Midwestern Regional Climate Center data for 1950–2021. For Polk County, home of Des Moines (Wikipedia), it lists an average last spring freeze of April 22 (early April 9, late May 4) and an average first fall freeze of October 10 (early September 26, late October 26). That is 171 days between the average dates, against NOAA's 184-day median for the Des Moines airport over 1991–2020. Different years, a county instead of one station and a different method all move the numbers; always note a source's data period.

Crop timing examples

Planting guides count from your own last frost date. UNH Extension's fact sheet gives offsets such as lettuce transplants 3–4 weeks before last frost, kale 4 weeks before, tomatoes 1–2 weeks after, peppers and basil 2 weeks after, and cucumbers 1–2 weeks after, with seeding of cucumbers and squash "when soil warms to 70°F." Applied to the NOAA 50% dates of two zone 5b cities (our arithmetic):

Crop (UNH offset)Des Moines, last frost Apr 18Concord, last frost May 8
Kale transplants (4 weeks before)Mar 21Apr 10
Lettuce transplants (3–4 weeks before)Mar 21–28Apr 10–17
Tomato transplants (1–2 weeks after)Apr 25–May 2May 15–22
Pepper and basil transplants (2 weeks after)May 2May 22
Cucumber transplants (1–2 weeks after)Apr 25–May 2May 15–22

Same zone, a three-week difference. UNH's own note for central New Hampshire is that "Memorial Day is a conservative estimate for the last frost date," which falls after Concord's 10% date of May 22. Enter your own dates in the planting calendar for 25 crops.

A zone-keyed table, and why it needs a date check

Few extension services key planting tables to zones. One that does is University of Illinois Extension in Cook County (Nancy Kreith, 2020), written for "Zone 5b surrounding Chicago" and a small zone 6a area near the lake:

CropCook County 2020 dates (In = start indoors, Out = transplant)
SpinachIn Mar 1, Out Mar 25, or sow in garden Mar 15–Apr 1; fall sowing Jul 15–Aug 15
PeasSow in garden Apr 1–25
BroccoliIn Mar 10–25, Out Apr 15–May 10
CarrotsSow in garden only, Apr 15–Jul 5
TomatoesIn Apr 1–May 1, Out May 10–Jun 5
Snap beansSow May 15 or when the temperature is above 55°F; repeat every two weeks until Jul 15
CucumbersIn peat pots Apr 25, Out May 25, or sow in garden May 15–30
PeppersIn peat pots Apr 5–20, Out May 20–Jun 10

The table predates the 2023 map. On USDA's ZIP search today, downtown Chicago (60601) is zone 6b (6a in 2012) and Matteson (60443), where the extension office that issued it is based, is 6a (5b in 2012). The publication assumes an average last spring frost of April 30, up to 5 days earlier near Lake Michigan; NOAA's 1991–2020 median for Chicago O'Hare is April 16. It also tells readers to "adjust planting dates to predicted last frosts," which is the step that matters.

Where the sources disagree

QuestionWhat the sources say
Fort Collins last frostNOAA 1991–2020: May 2 (50%), May 14 (10%). Colorado State Extension's PlantTalk: "the average date of last frost is May 15," with no data period stated, closer to NOAA's 10% date.
Omaha, a former zone 5 cityJohn Porter (Garden Professors), from NOAA/NWS data for about 30 years starting in 1980/81: 50% date April 21, 10% date May 4 for a 32°F frost. NOAA 1991–2020 for Omaha Eppley Airfield: April 18 and April 30. Omaha (68102) is also zone 6a on the 2023 map, 5b in 2012.
Chicago areaIllinois Extension Cook County (2020): zone 5b, last frost April 30. USDA 2023: zones 6a–6b at the ZIPs checked; NOAA O'Hare median April 16.
Can a zone time planting?University of Idaho: a zone "will not tell you how many frost-free days you will have." Illinois Extension keys its table to zones but says to adjust to predicted last frosts.

Using this page in a zone 5 garden

  1. Confirm your half zone with the ZIP search on USDA's map; three of the six cities above changed in 2023.
  2. Use the zone for plants that stay in the ground over winter; Iowa State describes the map as a guide for choosing trees, shrubs and perennials.
  3. Get frost dates for the station nearest you, in distance and elevation; see how to find your frost dates.
  4. Pick a probability: NC State calls the 10% spring date the low-risk, conservative choice, which suits frost-tender transplants; the 50% date is the median.
  5. Count your season, preferably the conservative 90% length, before choosing long-season varieties.
  6. Let soil temperature and the forecast override any calendar date.
Not every place in zone 5 is like these six. Each NOAA station describes its own spot, and local conditions shift dates: Illinois Extension notes frost dates up to 5 days different close to Lake Michigan. Treat any zone 5 planting chart without a stated frost date and data period as a rough guide only.

Sources

  1. USDA Agricultural Research Service — USDA Plant Hardiness Zone Map (interactive map and ZIP code search)
  2. Iowa State University Extension and Outreach — New Plant Hardiness Zone Map Released from the USDA (Aaron Steil, 2023)
  3. University of Illinois Extension — Shifting USDA plant hardiness map reflects changing climate, changes for plants (Emily Steele, 2024)
  4. NOAA NCEI — Access Data Service: U.S. Climate Normals 1991–2020, annual/seasonal 32°F freeze dates and growing season probabilities for the stations named on this page (CSV)
  5. NOAA NCEI — Readme for the 1991–2020 normals files (definitions of PRBLST, PRBFST and PRBGSL)
  6. NC State Extension — Interpreting Freeze/Frost Probabilities from the National Centers for Environmental Information (AG-873)
  7. Iowa State University Extension and Outreach, Yard and Garden — Frost and Freeze Dates in Iowa (MRCC data 1950–2021)
  8. Iowa State University Extension and Outreach, Yard and Garden — Frost and Freeze Dates in Iowa: O'Brien to Ringgold (incl. Polk County)
  9. Wikipedia — Des Moines, Iowa (secondary source; county only)
  10. University of Idaho Extension — Spring Vegetable Planting Guide for Idaho (BUL 965, Andy West, 2020, PDF)
  11. University of New Hampshire Extension — Growing Vegetables: When to Plant Your Vegetable Garden (fact sheet)
  12. University of Illinois Extension in Cook County — Vegetable Planting Dates and Annual Flower Planting Dates (Nancy Kreith, 2020, PDF)
  13. Colorado State University Extension, PlantTalk Colorado — 1809: Growing Warm Season Vegetables
  14. The Garden Professors — Planting Prognostication: Understanding last frost and planting dates (John Porter)

All sources were opened and checked in October 2026. Rules and figures change; confirm with the original before acting.