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Frost dates and planting calendar for Bozeman, Montana

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
5a[1]
Median last spring frost
May 26[2]
Median first fall frost
Sep 22[3]
Growing season, median
116 days[4]

Bozeman, Montana sits in USDA hardiness zone 5a[1]. In half of years the last spring frost comes after May 26, which is the median[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after May 9, half of years May 26, 1 in 10 years after Jun 14Last frostmedian May 26First fall frost: 9 in 10 years before Oct 5, half of years Sep 22, 1 in 10 years before Sep 5First frostmedian Sep 22Frost riskHardyHardy vegetables: plant Apr 28 to May 12Apr 28 to May 12Semi-hardySemi-hardy vegetables: plant May 12 to May 26May 12 to May 26TenderTender vegetables: plant around May 26around May 26Very tenderVery tender vegetables: plant from Jun 9from Jun 9
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

These dates come from NOAA climate normals for the Bozeman Montana State Univ weather station, using records from 1991 to 2020[5]. In 9 of 10 years the last spring frost comes after May 9, and in 1 of 10 years it comes after June 14[2]. For fall, the first frost comes before September 22 in half of years[3]. In 1 of 10 years it comes before September 5[3]. These are odds from past years and not a forecast, so any year can be earlier or later[2].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after May 9 after May 26 after June 14
First fall frost (32°F)[3] before September 5 before September 22 before October 5
  • Hard freeze (28°F): median last spring date May 8, median first fall date October 3[7].
  • Frost-free growing season: at least 93 days in 9 of 10 years, 116 days in half of years and 139 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Bozeman Montana State Univ (USC00241044), 1.5 miles from the city center, 4,913 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension's planting guide was written for Colorado, so its rules are applied here as a simple calculation[6]. Hardy vegetables such as peas, spinach and lettuce can go in as early as 2 to 4 weeks before the median last frost, which works out to April 28 to May 12[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before the median last frost, from May 12 up to the median date[9]. Tender vegetables such as snap beans and sweet corn can be seeded around the median last frost date, May 26[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after it, and June 9 is the earliest start[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (May 26) is April 28 to May 12[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (May 26) is May 12, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, May 26[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (May 26), is June 9[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Apr 28 Jul 2 (from transplants)
Cabbage (hardy)[12] Apr 28 Jul 22 (from transplants)
Kohlrabi (hardy)[12] Apr 28 Jun 17
Lettuce (hardy)[12] Apr 28 Jun 27
Onions (hardy)[12] Apr 28 Aug 16
Peas (hardy)[12] Apr 28 Jul 2
Radishes (hardy)[12] Apr 28 May 28
Spinach (hardy)[12] Apr 28 Jun 7
Turnips (hardy)[12] Apr 28 Jun 17
Beets (semi-hardy)[12] May 12 Jul 11
Carrots (semi-hardy)[12] May 12 Jul 21
Cauliflower (semi-hardy)[12] May 12 not listed
Parsnips (semi-hardy)[12] May 12 Jul 21
Potatoes (semi-hardy)[12] May 12 Sep 14
Swiss chard (semi-hardy)[12] May 12 Jul 11
Snap beans (tender)[12] May 26 Jul 25
Sweet corn (tender)[12] May 26 Jul 25
Cucumbers (tender)[12] May 26 Jul 20
Summer squash (tender)[12] May 26 Jul 15
Cantaloupe (very tender)[12] Jun 9 Sep 2
Eggplant (very tender)[12] Jun 9 Aug 8 (from transplants)
Peppers (very tender)[12] Jun 9 Aug 18 (from transplants)
Tomatoes (very tender)[12] Jun 9 Aug 13 (from transplants)
Winter squash (very tender)[12] Jun 9 Sep 17
Watermelon (very tender)[12] Jun 9 Sep 2
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

The 2023 USDA map puts the center of Bozeman in zone 5a, which means an average coldest night of -20°F to -15°F over 1991 to 2020[1]. The zone is based on winter cold, not on summer heat or frost dates[14]. Both ZIP code areas that overlap Bozeman are rated zone 5a, so the city does not span more than one zone in the ZIP data[15].

Zone 5a: average annual extreme minimum temperature -20°F to -15°F (1991 to 2020)[1]. Modeled value at the city center: -18.4°F[1].

Share of the city's land area by ZIP code zone: zone 5a 100%[15].

All towns in zone 5a and what zone 5a means

Zone by ZIP code
ZIP code Zone Coldest night range
59715[15] 5a -20 to -15°F
59718[15] 5a -20 to -15°F

Questions people ask

What growing zone is Bozeman?
The center of Bozeman is in USDA zone 5a on the 2023 map[1]. Both ZIP code areas that overlap the city are also rated 5a[15].
When is the last frost in Bozeman?
The median last spring frost is May 26, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after June 14[2].
When to plant tomatoes in Bozeman?
CSU Extension says very tender vegetables like tomatoes typically go in 2 or more weeks after the average last frost[11]. Using the median last frost, the earliest start is June 9[11].
When is the first frost in Bozeman?
The median first fall frost is September 22[3]. In 1 of 10 years it comes before September 5[3].
How long is the growing season in Bozeman?
The growing season is at least 116 days in half of years[4]. It is at least 93 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Bozeman, Montana in zone 5a. Zone 5a means an average annual extreme minimum temperature of -20°F to -15°F over 1991 to 2020. The map's modeled value at the city center is minus 18.4°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after May 9, in half of years after May 26, and in 1 of 10 years after June 14 (NOAA 1991 to 2020 normals). The median last frost date is May 26. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before September 5, in half of years before September 22, and in 9 of 10 years before October 5 (NOAA 1991 to 2020 normals). The median first frost date is September 22. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 93 days in 9 of 10 years, at least 116 days in half of years, and at least 139 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Bozeman Montana State Univ weather station (USC00241044), 1.5 miles from the center of Bozeman at 4,913 feet, using 30 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is May 8 and the median first fall date is October 3. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Bozeman, Montana overlaps 2 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 5a. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.