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

Planting zone for 59935 — Troy, MT

ZIP code 59935 (Troy, Lincoln County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 14 and the first fall frost September 25.

Where ZIP 59935 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 frostMay 14

First frostSep 25

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 Troy, 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 Troy, MT

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 14median — 50% chance of a later frost

Safe for tender plantsMay 31only 10% chance of frost after

First fall frostSeptember 25median — 10% chance by Sep 9

Growing season132 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 29 and returns around October 6.

From the NOAA station Troy, MT — 12 miles away, elevation 1,929 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 59935

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 2 – Apr 16

SpinachSow outdoors · Apr 2 – Apr 23

Broccoli, cabbageStart indoors · Mar 5 – Mar 19

Broccoli, cabbageTransplant · Apr 23 – May 7

Onion setsPlant outdoors · Apr 16 – Apr 30

PotatoesPlant outdoors · Apr 23 – May 7

LettuceSow outdoors · Apr 16 – Apr 30

Carrots, beetsSow outdoors · Apr 23 – May 7

TomatoesStart indoors · Mar 19 – Apr 2

TomatoesTransplant · May 21 – Jun 4

Peppers, eggplantStart indoors · Mar 5 – Mar 19

Peppers, eggplantTransplant · May 28 – Jun 11

BeansSow outdoors · May 21 – Jun 4

Sweet cornSow outdoors · May 21 – Jun 4

Cucumbers, squashSow outdoors · May 21 – Jun 4

Fall lettuce, spinachSow outdoors · Jul 31 – Aug 14

GarlicPlant cloves · Sep 11 – Oct 16

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 14) and first fall frost (Sep 25) 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 59935 came on Apr 26 — 5 days later than the 1991–2020 average (Apr 21).

average
Apr 212026
Apr 26

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 Troy, MT.

Soil in Troy, MT

The soil mapped at the center of ZIP 59935 is Andic Dystrochrepts — slightly decomposed plant material, well drained.

TextureSlightly decomposed plant materialtop layer

pH6.5neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter50%high

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Andic Dystrochrepts-Rock outcrop complex, glaciated mountain 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 59935; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Troy, MT

Summer high87 °Faverage high, July

Winter low23 °Faverage low, January

Hot days34days a year at 90 °F or more

Freezing nights152nights a year at 32 °F or less

Growing degree days1,931base 50 °F — the season’s usable heat

Longest day16 h 09 mindaylight on June 21

Shortest day8 h 16 mindaylight on December 21

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

Precipitation24.4 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: Troy, MT (12 mi away); precipitation: Troy, MT (12 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.

838456b

Moyie Springs, ID · 14 mi

Bonners Ferry, ID · 33 mi

599236a

Libby, MT · 35 mi

838116b

Clark Fork, ID · 40 mi

598536a

Noxon, MT · 42 mi

Montana planting zones →

Questions about 59935

What planting zone is ZIP code 59935?

ZIP code 59935 (Troy, 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 Troy, MT?

The median last spring frost (32 °F) near 59935 is May 14; after May 31 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Troy station.

When is the first frost in Troy, MT?

The median first fall frost near 59935 is September 25, giving a median frost-free growing season of 132 days.

When should I plant tomatoes in 59935?

Start tomato seeds indoors around Mar 19 – Apr 2 and set transplants outside around May 21 – Jun 4, one to three weeks after the median last frost.

How much rain and snow does 59935 get?

About 24.4 inches of precipitation a year (NOAA 1991–2020 normals, Troy station).

How hot do summers get in Troy, MT?

The average high peaks at 87 °F in July, with about 34 days a year at 90 °F or more.

What kind of soil does 59935 have?

The USDA soil survey maps Andic Dystrochrepts at the center of ZIP 59935: slightly decomposed plant material, well drained, pH about 6.5 (neutral).

Did spring come early in Troy, MT in 2026?

Spring leaf-out near 59935 came on Apr 26 in 2026, 5 days later than the 1991–2020 average (Apr 21), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Troy, MT?

Long-day onions: the longest day near 59935 is 16 h 09 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 59935 change?

Yes. The 2012 USDA map put 59935 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.