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Frost dates and planting calendar for Grass Valley, California

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

USDA hardiness zone
9a[1]
Median last spring frost
Apr 10[2]
Median first fall frost
Nov 13[3]
Growing season, median
215 days[4]

Grass Valley sits in USDA hardiness zone 9a at its center[1]. The median last spring frost is April 10, which means a last frost after that date in half of years[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 17, half of years Apr 10, 1 in 10 years after Apr 30Last frostmedian Apr 10First fall frost: 9 in 10 years before Dec 1, half of years Nov 13, 1 in 10 years before Oct 26First frostmedian Nov 13Frost riskHardyHardy vegetables: plant Mar 13 to Mar 27Mar 13 to Mar 27Semi-hardySemi-hardy vegetables: plant Mar 27 to Apr 10Mar 27 to Apr 10TenderTender vegetables: plant around Apr 10around Apr 10Very tenderVery tender vegetables: plant from Apr 24from Apr 24
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 Grass Valley #2 weather station, using records from 1991 to 2020[5]. In 9 of 10 years the last spring frost comes after March 17, and in 1 of 10 years it comes after April 30[2]. In the fall, the first frost comes before November 13 in half of years, and before October 26 in 1 of 10 years[3]. These dates are chances based on NOAA records from 1991 to 2020[2][3].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after March 17 after April 10 after April 30
First fall frost (32°F)[3] before October 26 before November 13 before December 1
  • Hard freeze (28°F): median last spring date March 9, median first fall date December 1[7].
  • Frost-free growing season: at least 188 days in 9 of 10 years, 215 days in half of years and 244 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 99.6% of years[8].
  • Weather station: Grass Valley #2 (USC00043573), 1.4 miles from the city center, 2,400 feet, 25 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension wrote its vegetable planting guide for Colorado, so we use its rules as a starting point for Grass Valley[6]. Hardy vegetables such as broccoli, lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which works out to March 13 to March 27[6]. Semi-hardy vegetables such as beets, carrots and potatoes can go in as early as 2 weeks before the median last frost, which is March 27[9]. Tender vegetables such as snap beans and sweet corn are started from seed around the median last frost date, April 10[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the median last frost, so the earliest start is April 24[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 10) is March 13 to March 27[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 10) is March 27, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 10[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 10), is April 24[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 13 May 17 (from transplants)
Cabbage (hardy)[12] Mar 13 Jun 6 (from transplants)
Kohlrabi (hardy)[12] Mar 13 May 2
Lettuce (hardy)[12] Mar 13 May 12
Onions (hardy)[12] Mar 13 Jul 1
Peas (hardy)[12] Mar 13 May 17
Radishes (hardy)[12] Mar 13 Apr 12
Spinach (hardy)[12] Mar 13 Apr 22
Turnips (hardy)[12] Mar 13 May 2
Beets (semi-hardy)[12] Mar 27 May 26
Carrots (semi-hardy)[12] Mar 27 Jun 5
Cauliflower (semi-hardy)[12] Mar 27 not listed
Parsnips (semi-hardy)[12] Mar 27 Jun 5
Potatoes (semi-hardy)[12] Mar 27 Jul 30
Swiss chard (semi-hardy)[12] Mar 27 May 26
Snap beans (tender)[12] Apr 10 Jun 9
Sweet corn (tender)[12] Apr 10 Jun 9
Cucumbers (tender)[12] Apr 10 Jun 4
Summer squash (tender)[12] Apr 10 May 30
Cantaloupe (very tender)[12] Apr 24 Jul 18
Eggplant (very tender)[12] Apr 24 Jun 23 (from transplants)
Peppers (very tender)[12] Apr 24 Jul 3 (from transplants)
Tomatoes (very tender)[12] Apr 24 Jun 28 (from transplants)
Winter squash (very tender)[12] Apr 24 Aug 2
Watermelon (very tender)[12] Apr 24 Jul 18
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 USDA zone is based on the average coldest night of each winter from 1991 to 2020, not on summer heat or frost dates[14]. Zone 9a means an average yearly low of 20°F to 25°F[1]. Grass Valley is mostly zone 9a by land area, at 92%, and the other 8% is zone 9b[15].

Zone 9a: average annual extreme minimum temperature 20°F to 25°F (1991 to 2020)[1]. Modeled value at the city center: 21.7°F[1].

Share of the city's land area by ZIP code zone: zone 9a 92%, zone 9b 8%[15].

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

Zone by ZIP code
ZIP code Zone Coldest night range
95945[15] 9a 20 to 25°F
95949[15] 9b 25 to 30°F
95959[15] 9a 20 to 25°F

Questions people ask

What growing zone is Grass Valley, California?
The 2023 USDA map puts the center of Grass Valley in zone 9a[1]. By land area, 92% of the city is in zone 9a and 8% is in zone 9b[15].
When is the last frost in Grass Valley?
The median last spring frost is April 10, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after April 30[2].
When is the first frost in Grass Valley?
The median first fall frost is November 13, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before October 26[3].
When to plant tomatoes in Grass Valley?
CSU Extension says very tender vegetables like tomatoes typically wait 2 or more weeks after the average last spring frost[11]. Using the median last frost, the earliest start is April 24[11].
How long is the growing season in Grass Valley?
The growing season is at least 215 days in half of years[4]. It is at least 188 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Grass Valley, California in zone 9a. Zone 9a means an average annual extreme minimum temperature of 20°F to 25°F over 1991 to 2020. The map's modeled value at the city center is 21.7°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 March 17, in half of years after April 10, and in 1 of 10 years after April 30 (NOAA 1991 to 2020 normals). The median last frost date is April 10. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before October 26, in half of years before November 13, and in 9 of 10 years before December 1 (NOAA 1991 to 2020 normals). The median first frost date is November 13. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 188 days in 9 of 10 years, at least 215 days in half of years, and at least 244 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Grass Valley #2 weather station (USC00043573), 1.4 miles from the center of Grass Valley at 2,400 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 March 9 and the median first fall date is December 1. 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 99.6% 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. Grass Valley, California overlaps 3 ZIP code areas. By land area, 92% lies in ZIP code areas rated zone 9a, 8% 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.