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Frost dates and planting calendar for Concord, 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
Mar 8[2]
Median first fall frost
Dec 22[3]
Growing season, median
282 days[4]

Concord, California sits in USDA hardiness zone 9b[1]. The median last spring frost is March 8, so in half of years the last 32°F frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Jan 12, half of years Mar 8, 1 in 10 years after Apr 15Last frostmedian Mar 8First frostmedian Dec 22Frost riskHardyHardy vegetables: plant Feb 8 to Feb 22Feb 8 to Feb 22Semi-hardySemi-hardy vegetables: plant Feb 22 to Mar 8Feb 22 to Mar 8TenderTender vegetables: plant around Mar 8around Mar 8Very tenderVery tender vegetables: plant from Mar 22from Mar 22
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.

NOAA frost dates are odds from 1991 to 2020 records, not a forecast. In 9 of 10 years the last spring frost comes after January 12, and in 1 of 10 years it comes after April 15[2]. For fall, the median first frost is December 22, and in 1 of 10 years the first frost comes before November 23[3]. These dates come from the Mt Diablo Junction station, which sits at 2,170 feet outside the city center[5].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after January 12 after March 8 after April 15
First fall frost (32°F)[3] before November 23 before December 22 before February 11
  • Hard freeze (28°F): median last spring date February 8, median first fall date January 16[7].
  • Frost-free growing season: at least 238 days in 9 of 10 years, 282 days in half of years and 343 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 95.9% of years and 28°F or colder in 49.5% of years[8].
  • Weather station: Mt Diablo Junction (USC00045915), 7.5 miles from the city center, 2,170 feet, 25 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension groups vegetables by how they handle frost. Its guide was written for Colorado, so its rules were not tuned for Concord[6]. Hardy vegetables such as broccoli, lettuce and peas can go in as early as 2 to 4 weeks before the median last frost, which is February 8 to February 22 here[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before the median last frost, from February 22 up to March 8[9]. Tender vegetables such as snap beans and sweet corn go in from seed around the median last frost, March 8[10]. Very tender vegetables such as tomatoes and peppers typically start 2 or more weeks after it, with the earliest start on March 22[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (March 8) is February 8 to February 22[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (March 8) is February 22, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, March 8[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (March 8), is March 22[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Feb 8 Apr 14 (from transplants)
Cabbage (hardy)[12] Feb 8 May 4 (from transplants)
Kohlrabi (hardy)[12] Feb 8 Mar 30
Lettuce (hardy)[12] Feb 8 Apr 9
Onions (hardy)[12] Feb 8 May 29
Peas (hardy)[12] Feb 8 Apr 14
Radishes (hardy)[12] Feb 8 Mar 10
Spinach (hardy)[12] Feb 8 Mar 20
Turnips (hardy)[12] Feb 8 Mar 30
Beets (semi-hardy)[12] Feb 22 Apr 23
Carrots (semi-hardy)[12] Feb 22 May 3
Cauliflower (semi-hardy)[12] Feb 22 not listed
Parsnips (semi-hardy)[12] Feb 22 May 3
Potatoes (semi-hardy)[12] Feb 22 Jun 27
Swiss chard (semi-hardy)[12] Feb 22 Apr 23
Snap beans (tender)[12] Mar 8 May 7
Sweet corn (tender)[12] Mar 8 May 7
Cucumbers (tender)[12] Mar 8 May 2
Summer squash (tender)[12] Mar 8 Apr 27
Cantaloupe (very tender)[12] Mar 22 Jun 15
Eggplant (very tender)[12] Mar 22 May 21 (from transplants)
Peppers (very tender)[12] Mar 22 May 31 (from transplants)
Tomatoes (very tender)[12] Mar 22 May 26 (from transplants)
Winter squash (very tender)[12] Mar 22 Jun 30
Watermelon (very tender)[12] Mar 22 Jun 15
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

Zone 9b means the coldest night of the year averages 25°F to 30°F, based on 1991 to 2020[1]. The zone comes from winter lows, not from summer heat or frost dates[14]. All 8 ZIP code areas that overlap Concord are rated zone 9b by land area, so the city does not span more than one zone[15].

Zone 9b: average annual extreme minimum temperature 25°F to 30°F (1991 to 2020)[1]. Modeled value at the city center: 27.8°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
94521[15] 9b 25 to 30°F
94520[15] 9b 25 to 30°F
94518[15] 9b 25 to 30°F
94565[15] 9b 25 to 30°F
94519[15] 9b 25 to 30°F
94517[15] 9b 25 to 30°F
94523[15] 9b 25 to 30°F
94553[15] 9b 25 to 30°F

Questions people ask

What growing zone is Concord, California?
The 2023 USDA map puts the center of Concord in zone 9b[1].
When is the last frost in Concord?
The median last spring frost is March 8, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after April 15[2].
When to plant tomatoes in Concord?
CSU Extension lists tomatoes as very tender, typically planted 2 or more weeks after the average last frost[11]. Using the median last frost, the earliest start is March 22[11].
When is the first frost in Concord?
The median first fall frost is December 22, and in 1 of 10 years it comes before November 23[3].
How long is the growing season in Concord?
The growing season is at least 282 days in half of years[4]. It is at least 238 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Concord, 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 27.8°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 12, in half of years after March 8, and in 1 of 10 years after April 15 (NOAA 1991 to 2020 normals). The median last frost date is March 8. 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 23, in half of years before December 22, and in 9 of 10 years before February 11 (NOAA 1991 to 2020 normals). The median first frost date is December 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 238 days in 9 of 10 years, at least 282 days in half of years, and at least 343 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Mt Diablo Junction weather station (USC00045915), 7.5 miles from the center of Concord at 2,170 feet, using 25 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 February 8 and the median first fall date is January 16. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 95.9% of years from 1991 to 2020, and 28°F or colder in 49.5% 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. Concord, California overlaps 8 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.