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

Planting zone for 59830 — De Borgia, MT

ZIP code 59830 (De Borgia, Mineral County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is June 10 and the first fall frost September 23.

Where ZIP 59830 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.

Zone6a−10 to −5 °F

Coldest night−23.3 to −20.6 °C

Last frostJun 10

First frostSep 23

2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for De Borgia, MT…

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 De Borgia, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostJune 10median — 50% chance of a later frost

Safe for tender plantsJune 25only 10% chance of frost after

First fall frostSeptember 23median — 10% chance by Sep 4

Growing season104 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 21 and returns around October 5.

From the NOAA station Mullan Pass Vor/Dme, ID — 9 miles away, elevation 6,027 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 59830

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 29 – May 13

SpinachSow outdoors · Apr 29 – May 20

Broccoli, cabbageStart indoors · Apr 1 – Apr 15

Broccoli, cabbageTransplant · May 20 – Jun 3

Onion setsPlant outdoors · May 13 – May 27

PotatoesPlant outdoors · May 20 – Jun 3

LettuceSow outdoors · May 13 – May 27

Carrots, beetsSow outdoors · May 20 – Jun 3

TomatoesStart indoors · Apr 15 – Apr 29

TomatoesTransplant · Jun 17 – Jul 1

Peppers, eggplantStart indoors · Apr 1 – Apr 15

Peppers, eggplantTransplant · Jun 24 – Jul 8

BeansSow outdoors · Jun 17 – Jul 1

Sweet cornSow outdoors · Jun 17 – Jul 1

Cucumbers, squashSow outdoors · Jun 17 – Jul 1

Fall lettuce, spinachSow outdoors · Jul 29 – Aug 12

GarlicPlant cloves · Sep 9 – Oct 14

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 10) and first fall frost (Sep 23) 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 59830 came on Apr 27 — about the same time as the 1991–2020 average (Apr 26).

average
Apr 262026
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 6a in Montana

572 plants native to the lower 48 states, recorded in Montana, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. 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 De Borgia, MT.

Soil in De Borgia, MT

The soil mapped at the center of ZIP 59830 is Rumblecreek — mucky peat, well drained.

TextureMucky peattop layer

pH5.0strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter70%high

Hydrologic groupBwater soaks in moderately

Farmland classprime farmlandUSDA classification

Map unit: Rumblecreek-Sol families, complex, colluvial aprons and alluvial fans, very stony.

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 59830; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in De Borgia, MT

Summer high84 °Faverage high, July

Winter low17 °Faverage low, January

Hot days24days a year at 90 °F or more

Freezing nights215nights a year at 32 °F or less

Growing degree days1,217base 50 °F — the season’s usable heat

Longest day15 h 58 mindaylight on June 21

Shortest day8 h 27 mindaylight on December 21

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

Precipitation37 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: Haugan 1 W, MT (4 mi away); precipitation: Haugan 1 W, MT (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Saint Regis, MT · 17 mi

598736a

Thompson Falls, MT · 18 mi

Montana planting zones →

Questions about 59830

What planting zone is ZIP code 59830?

ZIP code 59830 (De Borgia, MT) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in De Borgia, MT?

The median last spring frost (32 °F) near 59830 is June 10; after June 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Mullan Pass Vor/Dme station.

When is the first frost in De Borgia, MT?

The median first fall frost near 59830 is September 23, giving a median frost-free growing season of 104 days.

When should I plant tomatoes in 59830?

Start tomato seeds indoors around Apr 15 – Apr 29 and set transplants outside around Jun 17 – Jul 1, one to three weeks after the median last frost.

How much rain and snow does 59830 get?

About 37 inches of precipitation a year (NOAA 1991–2020 normals, Haugan 1 W station).

How hot do summers get in De Borgia, MT?

The average high peaks at 84 °F in July, with about 24 days a year at 90 °F or more.

What kind of soil does 59830 have?

The USDA soil survey maps Rumblecreek at the center of ZIP 59830: mucky peat, well drained, pH about 5.0 (strongly acidic).

Did spring come early in De Borgia, MT in 2026?

Spring leaf-out near 59830 came on Apr 27 in 2026, about the same as the 1991–2020 average (Apr 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in De Borgia, MT?

Long-day onions: the longest day near 59830 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59830 change?

Yes. The 2012 USDA map put 59830 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.