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

Planting zone for 58631 — Glen Ullin, ND

ZIP code 58631 (Glen Ullin, Morton County) is in USDA zone 4a: the coldest winter night averages −30 to −25 °F. The median last spring frost is May 19 and the first fall frost September 21.

Where ZIP 58631 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 19
First frostSep 21
2012 zone4a

Same zone as on the 2012 map. 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 Glen Ullin, 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 Glen Ullin, ND

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 19median — 50% chance of a later frost
Safe for tender plantsJune 2only 10% chance of frost after
First fall frostSeptember 21median — 10% chance by Sep 7
Growing season123 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 10 and returns around September 30.

From the NOAA station Hebron, ND — 12 miles away, elevation 2,159 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 58631

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 7 – Apr 21
SpinachSow outdoors · Apr 7 – Apr 28
Broccoli, cabbageStart indoors · Mar 10 – Mar 24
Broccoli, cabbageTransplant · Apr 28 – May 12
Onion setsPlant outdoors · Apr 21 – May 5
PotatoesPlant outdoors · Apr 28 – May 12
LettuceSow outdoors · Apr 21 – May 5
Carrots, beetsSow outdoors · Apr 28 – May 12
TomatoesStart indoors · Mar 24 – Apr 7
TomatoesTransplant · May 26 – Jun 9
Peppers, eggplantStart indoors · Mar 10 – Mar 24
Peppers, eggplantTransplant · Jun 2 – Jun 16
BeansSow outdoors · May 26 – Jun 9
Sweet cornSow outdoors · May 26 – Jun 9
Cucumbers, squashSow outdoors · May 26 – Jun 9
Fall lettuce, spinachSow outdoors · Jul 27 – Aug 10
GarlicPlant cloves · Sep 7 – Oct 12
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 19) and first fall frost (Sep 21) 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 58631 came on Apr 16 — 3 days earlier than the 1991–2020 average (Apr 19).

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 Glen Ullin, ND.

Soil in Glen Ullin, ND

The soil mapped at the center of ZIP 58631 is Dogtooth — loam, well drained.

TextureLoama good balance for most vegetables
pH6.8neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Dogtooth-Janesburg complex, 0 to 6 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 58631; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Glen Ullin, ND

Summer high82 °Faverage high, July
Winter low3 °Faverage low, January
Hot days15days a year at 90 °F or more
Freezing nights194nights a year at 32 °F or less
Growing degree days1,998base 50 °F — the season’s usable heat
Longest day15 h 52 mindaylight on June 21
Shortest day8 h 32 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation18.4 inper year, rain and melted snow
Snowfall41 inper year

Average high and low, by month

−10°0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 24 °F, low 3 °F 24°3° JanFebruary: average high 28 °F, low 7 °F 28°7° FebMarch: average high 40 °F, low 17 °F 40°17° MarApril: average high 54 °F, low 28 °F 54°28° AprMay: average high 66 °F, low 40 °F 66°40° MayJune: average high 75 °F, low 50 °F 75°50° JunJuly: average high 82 °F, low 55 °F 82°55° JulAugust: average high 82 °F, low 53 °F 82°53° AugSeptember: average high 72 °F, low 43 °F 72°43° SepOctober: average high 56 °F, low 30 °F 56°30° OctNovember: average high 40 °F, low 18 °F 40°18° NovDecember: average high 28 °F, low 8 °F 28°8° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″January: 0.41 in precipitation, 5.2 in snowfall 0.4❄5 JanFebruary: 0.48 in precipitation, 6.2 in snowfall 0.5❄6 FebMarch: 0.86 in precipitation, 7.4 in snowfall 0.9❄7 MarApril: 1.51 in precipitation, 4 in snowfall 1.5❄4 AprMay: 2.58 in precipitation, 0.8 in snowfall 2.6❄1 MayJune: 3.30 in precipitation 3.3 JunJuly: 2.86 in precipitation 2.9 JulAugust: 2.00 in precipitation 2.0 AugSeptember: 1.89 in precipitation, 0.2 in snowfall 1.9 SepOctober: 1.48 in precipitation, 2.5 in snowfall 1.5❄3 OctNovember: 0.62 in precipitation, 6.6 in snowfall 0.6❄7 NovDecember: 0.43 in precipitation, 7.7 in snowfall 0.4❄8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Hebron, ND (12 mi away); precipitation: Hebron, ND (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

586384a
Hebron, ND · 13 mi
585204a
Almont, ND · 15 mi
585634a
New Salem, ND · 20 mi
586524a
Richardton, ND · 20 mi
585334a
Elgin, ND · 28 mi
585624a
New Leipzig, ND · 31 mi
586564a
Taylor, ND · 32 mi
586414b
Lefor, ND · 32 mi

North Dakota planting zones →

Questions about 58631

What planting zone is ZIP code 58631?

ZIP code 58631 (Glen Ullin, 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 Glen Ullin, ND?

The median last spring frost (32 °F) near 58631 is May 19; after June 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Hebron station.

When is the first frost in Glen Ullin, ND?

The median first fall frost near 58631 is September 21, giving a median frost-free growing season of 123 days.

When should I plant tomatoes in 58631?

Start tomato seeds indoors around Mar 24 – Apr 7 and set transplants outside around May 26 – Jun 9, one to three weeks after the median last frost.

How much rain and snow does 58631 get?

About 18.4 inches of precipitation a year and 41 inches of snowfall (NOAA 1991–2020 normals, Hebron station).

How hot do summers get in Glen Ullin, ND?

The average high peaks at 82 °F in July, with about 15 days a year at 90 °F or more.

What kind of soil does 58631 have?

The USDA soil survey maps Dogtooth at the center of ZIP 58631: loam, well drained, pH about 6.8 (neutral).

Did spring come early in Glen Ullin, ND in 2026?

Spring leaf-out near 58631 came on Apr 16 in 2026, 3 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Glen Ullin, ND?

Long-day onions: the longest day near 58631 is 15 h 52 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).