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

Planting zone for 58343 — Knox, ND

ZIP code 58343 (Knox, Benson County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 11 and the first fall frost September 28.

Where ZIP 58343 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.

Zone4a−30 to −25 °F
Coldest night−34.4 to −31.7 °C
Last frostMay 11
First frostSep 28
2012 zone3b

Was 3b 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 4a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Knox, ND…

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 Knox, ND

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 11median — 50% chance of a later frost
Safe for tender plantsMay 23only 10% chance of frost after
First fall frostSeptember 28median — 10% chance by Sep 18
Growing season138 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around October 6.

From the NOAA station Esmond 9 Nnw, ND — 11 miles away, elevation 1,631 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 58343

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 30 – Apr 13
SpinachSow outdoors · Mar 30 – Apr 20
Broccoli, cabbageStart indoors · Mar 2 – Mar 16
Broccoli, cabbageTransplant · Apr 20 – May 4
Onion setsPlant outdoors · Apr 13 – Apr 27
PotatoesPlant outdoors · Apr 20 – May 4
LettuceSow outdoors · Apr 13 – Apr 27
Carrots, beetsSow outdoors · Apr 20 – May 4
TomatoesStart indoors · Mar 16 – Mar 30
TomatoesTransplant · May 18 – Jun 1
Peppers, eggplantStart indoors · Mar 2 – Mar 16
Peppers, eggplantTransplant · May 25 – Jun 8
BeansSow outdoors · May 18 – Jun 1
Sweet cornSow outdoors · May 18 – Jun 1
Cucumbers, squashSow outdoors · May 18 – Jun 1
Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17
GarlicPlant cloves · Sep 14 – Oct 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 11) and first fall frost (Sep 28) 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 58343 came on May 4 — 7 days later than the 1991–2020 average (Apr 27).

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 4a in North Dakota

342 plants native to the lower 48 states, recorded in North Dakota, and rated by the USDA to survive −30 °F or colder — the bottom of zone 4a. Each links to its USDA PLANTS profile.

Trees 21

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fbigtooth aspen65 ft · blooms mid spring · high shade tolerance · to −43 °Fblack ash65 ft · blooms early spring · high shade tolerance · to −47 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °F

Shrubs 56

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fbeaked hazelnut15 ft · blooms early spring · low shade tolerance · to −47 °Fbig sagebrush4 ft · blooms mid summer · high shade tolerance · to −43 °F

Wildflowers & perennials 146

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican speedwell0.8 ft · blooms mid summer · low shade tolerance · to −38 °F

Grasses 110

alkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °F

Vines 4

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

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 Knox, ND.

Soil in Knox, ND

The soil mapped at the center of ZIP 58343 is Fram — loam, somewhat poorly drained.

TextureLoama good balance for most vegetables
pH7.9alkaline; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter4%moderate
Hydrologic groupCwater soaks in slowly
Farmland classprime farmlandUSDA classification

Map unit: Fram-Wyard loams, 0 to 3 percent slopes.

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 58343; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Knox, ND

Summer high80 °Faverage high, July
Winter low−4 °Faverage low, January
Hot days6days a year at 90 °F or more
Freezing nights189nights a year at 32 °F or less
Growing degree days2,018base 50 °F — the season’s usable heat
Longest day16 h 06 mindaylight on June 21
Shortest day8 h 19 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation21 inper year, rain and melted snow
Snowfall43 inper year

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 15 °F, low -4 °F 15°−4° JanFebruary: average high 20 °F, low -1 °F 20°−1° FebMarch: average high 33 °F, low 13 °F 33°13° MarApril: average high 51 °F, low 28 °F 51°28° AprMay: average high 66 °F, low 42 °F 66°42° MayJune: average high 74 °F, low 53 °F 74°53° JunJuly: average high 80 °F, low 57 °F 80°57° JulAugust: average high 80 °F, low 55 °F 80°55° AugSeptember: average high 71 °F, low 45 °F 71°45° SepOctober: average high 54 °F, low 31 °F 54°31° OctNovember: average high 36 °F, low 16 °F 36°16° NovDecember: average high 22 °F, low 3 °F 22°3° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″January: 0.49 in precipitation, 8 in snowfall 0.5❄8 JanFebruary: 0.54 in precipitation, 6.4 in snowfall 0.5❄6 FebMarch: 0.90 in precipitation, 6.5 in snowfall 0.9❄7 MarApril: 1.31 in precipitation, 2.9 in snowfall 1.3❄3 AprMay: 3.01 in precipitation, 0.9 in snowfall 3.0❄1 MayJune: 3.83 in precipitation 3.8 JunJuly: 3.68 in precipitation 3.7 JulAugust: 2.15 in precipitation 2.1 AugSeptember: 1.75 in precipitation 1.8 SepOctober: 1.41 in precipitation, 3.3 in snowfall 1.4❄3 OctNovember: 0.92 in precipitation, 7.4 in snowfall 0.9❄7 NovDecember: 0.99 in precipitation, 8 in snowfall 1.0❄8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Esmond 9 Nnw, ND (11 mi away); precipitation: Rugby, ND (13 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

4 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

583864a
York, ND · 6 mi
583853b
Wolford, ND · 13 mi
583464a
Leeds, ND · 14 mi
583324a
Esmond, ND · 18 mi
583103b
Agate, ND · 20 mi
583514a
Minnewaukan, ND · 23 mi
583533b
Mylo, ND · 25 mi
583663b
Rolette, ND · 26 mi

North Dakota planting zones →

Questions about 58343

What planting zone is ZIP code 58343?

ZIP code 58343 (Knox, ND) is in USDA hardiness zone 4a on the 2023 map: the coldest night of an average winter reaches −30 to −25 °F (−34.4 to −31.7 °C).

When is the last frost in Knox, ND?

The median last spring frost (32 °F) near 58343 is May 11; after May 23 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Esmond 9 Nnw station.

When is the first frost in Knox, ND?

The median first fall frost near 58343 is September 28, giving a median frost-free growing season of 138 days.

When should I plant tomatoes in 58343?

Start tomato seeds indoors around Mar 16 – Mar 30 and set transplants outside around May 18 – Jun 1, one to three weeks after the median last frost.

How much rain and snow does 58343 get?

About 21 inches of precipitation a year and 43 inches of snowfall (NOAA 1991–2020 normals, Rugby station).

How hot do summers get in Knox, ND?

The average high peaks at 80 °F in July, with about 6 days a year at 90 °F or more.

What kind of soil does 58343 have?

The USDA soil survey maps Fram at the center of ZIP 58343: loam, somewhat poorly drained, pH about 7.9 (alkaline).

Did spring come early in Knox, ND in 2026?

Spring leaf-out near 58343 came on May 4 in 2026, 7 days later than the 1991–2020 average (Apr 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Knox, ND?

Long-day onions: the longest day near 58343 is 16 h 06 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 58343 change?

Yes. The 2012 USDA map put 58343 in zone 3b; the 2023 map puts it in zone 4a. The newer map uses 1991–2020 data and more weather stations.