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Frost dates and planting calendar for Napa, California

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

USDA hardiness zone
9b[1]
Median last spring frost
Feb 12[2]
Median first fall frost
Dec 4[3]
Growing season, median
299 days[4]

Napa is in USDA hardiness zone 9b[1]. The median last spring frost at the nearby NOAA station is February 12[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Jan 3, half of years Feb 12, 1 in 10 years after Mar 13Last frostmedian Feb 12First frostmedian Dec 4Frost riskHardyHardy vegetables: plant Jan 15 to Jan 29Jan 15 to Jan 29Semi-hardySemi-hardy vegetables: plant Jan 29 to Feb 12Jan 29 to Feb 12TenderTender vegetables: plant around Feb 12around Feb 12Very tenderVery tender vegetables: plant from Feb 26from Feb 26
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 frost dates come from NOAA climate normals for the Napa State Hospital station near the center of Napa[5]. They use records from 1991 to 2020. The median last spring frost is February 12, so in half of years the last frost comes after that date[2]. In 1 of 10 years the last frost comes after March 13[2]. In half of years the first fall frost comes before December 4[3]. These are chances, not promises, and any year can be earlier or later.

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after January 3 after February 12 after March 13
First fall frost (32°F)[3] before November 15 before December 4 before January 4
  • Hard freeze (28°F): median last spring date January 11, median first fall date December 19[7].
  • Frost-free growing season: at least 257 days in 9 of 10 years, 299 days in half of years and 338 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 98.4% of years and 28°F or colder in 71% of years[8].
  • Weather station: Napa State Hospital (USC00046074), 2.4 miles from the city center, 35 feet, 28 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension wrote its vegetable planting guide for Colorado, so treat these dates as a starting point[6]. We took the NOAA median last frost of February 12 as the average last frost[6]. Hardy vegetables such as broccoli, lettuce and peas can go in as early as 2 to 4 weeks before it, which is January 15 to January 29[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before it, which is January 29[9]. Tender vegetables such as snap beans and sweet corn can be sown from seed around February 12[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after it, and February 26 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 (February 12) is January 15 to January 29[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (February 12) is January 29, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, February 12[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (February 12), is February 26[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Jan 15 Mar 21 (from transplants)
Cabbage (hardy)[12] Jan 15 Apr 10 (from transplants)
Kohlrabi (hardy)[12] Jan 15 Mar 6
Lettuce (hardy)[12] Jan 15 Mar 16
Onions (hardy)[12] Jan 15 May 5
Peas (hardy)[12] Jan 15 Mar 21
Radishes (hardy)[12] Jan 15 Feb 14
Spinach (hardy)[12] Jan 15 Feb 24
Turnips (hardy)[12] Jan 15 Mar 6
Beets (semi-hardy)[12] Jan 29 Mar 30
Carrots (semi-hardy)[12] Jan 29 Apr 9
Cauliflower (semi-hardy)[12] Jan 29 not listed
Parsnips (semi-hardy)[12] Jan 29 Apr 9
Potatoes (semi-hardy)[12] Jan 29 Jun 3
Swiss chard (semi-hardy)[12] Jan 29 Mar 30
Snap beans (tender)[12] Feb 12 Apr 13
Sweet corn (tender)[12] Feb 12 Apr 13
Cucumbers (tender)[12] Feb 12 Apr 8
Summer squash (tender)[12] Feb 12 Apr 3
Cantaloupe (very tender)[12] Feb 26 May 22
Eggplant (very tender)[12] Feb 26 Apr 27 (from transplants)
Peppers (very tender)[12] Feb 26 May 7 (from transplants)
Tomatoes (very tender)[12] Feb 26 May 2 (from transplants)
Winter squash (very tender)[12] Feb 26 Jun 6
Watermelon (very tender)[12] Feb 26 May 22
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

A zone shows the average coldest night of the winter from 1991 to 2020, not summer heat or frost dates[14]. Zone 9b means an average yearly low of 25°F to 30°F[1]. Napa overlaps 3 ZIP code areas, and by land area 100% lies in zone 9b areas[15].

Zone 9b: average annual extreme minimum temperature 25°F to 30°F (1991 to 2020)[1]. Modeled value at the city center: 25.9°F[1].

Share of the city's land area by ZIP code zone: zone 9b 100%[15].

All towns in zone 9b and what zone 9b means

Zone by ZIP code
ZIP code Zone Coldest night range
94558[15] 9b 25 to 30°F
94559[15] 9b 25 to 30°F
94503[15] 9b 25 to 30°F

Questions people ask

What growing zone is Napa, California?
The center of Napa is in USDA zone 9b[1]. All of the city's land area lies in ZIP code areas rated 9b[15].
When is the last frost in Napa?
The median last spring frost is February 12[2]. In 9 of 10 years the last frost comes after January 3, and in 1 of 10 years after March 13[2].
When is the first frost in Napa?
The median first fall frost is December 4[3]. In 1 of 10 years the first frost comes before November 15[3].
When to plant tomatoes in Napa?
CSU Extension typically starts tomatoes 2 or more weeks after the average last frost, and that earliest start works out to February 26 in Napa[11]. The CSU guide was written for Colorado[11].
How long is the growing season in Napa?
In half of years the season between the last spring and first fall frost is at least 299 days[4]. In 9 of 10 years it is at least 257 days[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Napa, California in zone 9b. Zone 9b means an average annual extreme minimum temperature of 25°F to 30°F over 1991 to 2020. The map's modeled value at the city center is 25.9°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 January 3, in half of years after February 12, and in 1 of 10 years after March 13 (NOAA 1991 to 2020 normals). The median last frost date is February 12. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before November 15, in half of years before December 4, and in 9 of 10 years before January 4 (NOAA 1991 to 2020 normals). The median first frost date is December 4. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 257 days in 9 of 10 years, at least 299 days in half of years, and at least 338 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Napa State Hospital weather station (USC00046074), 2.4 miles from the center of Napa at 35 feet, using 28 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 January 11 and the median first fall date is December 19. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 98.4% of years from 1991 to 2020, and 28°F or colder in 71% 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. Napa, California overlaps 3 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 9b. 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.