Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 55040 — Isanti, MN

ZIP code 55040 (Isanti, Isanti County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 2 and the first fall frost October 4.

Where ZIP 55040 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone4b−25 to −20 °F

Coldest night−31.7 to −28.9 °C

Last frostMay 2

First frostOct 4

2012 zone4a

Was 4a on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Isanti, MN…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Isanti, MN

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMay 2median — 50% chance of a later frost

Safe for tender plantsMay 20only 10% chance of frost after

First fall frostOctober 4median — 10% chance by Sep 20

Growing season153 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 21 and returns around October 15.

From the NOAA station Cambridge, MN — 6 miles away, elevation 965 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 55040

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 21 – Apr 4

SpinachSow outdoors · Mar 21 – Apr 11

Broccoli, cabbageStart indoors · Feb 21 – Mar 7

Broccoli, cabbageTransplant · Apr 11 – Apr 25

Onion setsPlant outdoors · Apr 4 – Apr 18

PotatoesPlant outdoors · Apr 11 – Apr 25

LettuceSow outdoors · Apr 4 – Apr 18

Carrots, beetsSow outdoors · Apr 11 – Apr 25

TomatoesStart indoors · Mar 7 – Mar 21

TomatoesTransplant · May 9 – May 23

Peppers, eggplantStart indoors · Feb 21 – Mar 7

Peppers, eggplantTransplant · May 16 – May 30

BeansSow outdoors · May 9 – May 23

Sweet cornSow outdoors · May 9 – May 23

Cucumbers, squashSow outdoors · May 9 – May 23

Fall lettuce, spinachSow outdoors · Aug 9 – Aug 23

GarlicPlant cloves · Sep 20 – Oct 25

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 2) and first fall frost (Oct 4) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 55040 came on Apr 15 — 3 days earlier than the 1991–2020 average (Apr 18).

average
Apr 182026
Apr 15

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 4b in Minnesota

497 plants native to the lower 48 states, recorded in Minnesota, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Isanti, MN.

Soil in Isanti, MN

The soil mapped at the center of ZIP 55040 is Elkriver — fine sandy loam, somewhat poorly drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding

pH5.4strongly acidic; most vegetables like 6.0–7.0

DrainageSomewhat poorly drainedconsider raised beds

Organic matter1.7%low — add compost

Hydrologic groupA/Ddrains fast once dried out; wet otherwise

Farmland classPrime farmland if drainedUSDA classification

Map unit: Elkriver fine sandy loam, occasionally flooded.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 55040; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Isanti, MN

Summer high82 °Faverage high, July

Winter low4 °Faverage low, January

Hot days5days a year at 90 °F or more

Freezing nights171nights a year at 32 °F or less

Growing degree days2,484base 50 °F — the season’s usable heat

Longest day15 h 41 mindaylight on June 21

Shortest day8 h 42 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation32 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Cambridge, MN (6 mi away); precipitation: Saint Francis 4.0 E, MN (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 4b.

550704b

Saint Francis, MN · 4 mi

Stanchfield, MN · 14 mi

553034b

Anoka, MN · 15 mi

Minnesota planting zones →

Questions about 55040

What planting zone is ZIP code 55040?

ZIP code 55040 (Isanti, MN) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Isanti, MN?

The median last spring frost (32 °F) near 55040 is May 2; after May 20 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Cambridge station.

When is the first frost in Isanti, MN?

The median first fall frost near 55040 is October 4, giving a median frost-free growing season of 153 days.

When should I plant tomatoes in 55040?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 55040 get?

About 32 inches of precipitation a year (NOAA 1991–2020 normals, Saint Francis 4.0 E station).

How hot do summers get in Isanti, MN?

The average high peaks at 82 °F in July, with about 5 days a year at 90 °F or more.

What kind of soil does 55040 have?

The USDA soil survey maps Elkriver at the center of ZIP 55040: fine sandy loam, somewhat poorly drained, pH about 5.4 (strongly acidic).

Did spring come early in Isanti, MN in 2026?

Spring leaf-out near 55040 came on Apr 15 in 2026, 3 days earlier than the 1991–2020 average (Apr 18), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Isanti, MN?

Long-day onions: the longest day near 55040 is 15 h 41 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 55040 change?

Yes. The 2012 USDA map put 55040 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.