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Frost dates and planting calendar for Kennewick, Washington

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

USDA hardiness zone
7b[1]
Median last spring frost
Mar 28[2]
Median first fall frost
Oct 30[3]
Growing season, median
216 days[4]

Kennewick, Washington is in USDA hardiness zone 7b[1]. NOAA records from 1991 to 2020 put the median last spring frost at March 28[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 9, half of years Mar 28, 1 in 10 years after Apr 10Last frostmedian Mar 28First fall frost: 9 in 10 years before Nov 15, half of years Oct 30, 1 in 10 years before Oct 18First frostmedian Oct 30Frost riskHardyHardy vegetables: plant Feb 28 to Mar 14Feb 28 to Mar 14Semi-hardySemi-hardy vegetables: plant Mar 14 to Mar 28Mar 14 to Mar 28TenderTender vegetables: plant around Mar 28around Mar 28Very tenderVery tender vegetables: plant from Apr 11from Apr 11
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 are odds, not a forecast. At the Kennewick weather station, the last spring frost (32°F) comes after March 9 in 9 of 10 years, after March 28 in half of years, and after April 10 in 1 of 10 years[2]. The first fall frost comes before October 18 in 1 of 10 years, before October 30 in half of years, and before November 15 in 9 of 10 years[3]. NOAA based these numbers on 27 years of records at the Kennewick station[5]. 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 March 9 after March 28 after April 10
First fall frost (32°F)[3] before October 18 before October 30 before November 15
  • Hard freeze (28°F): median last spring date March 8, median first fall date November 11[7].
  • Frost-free growing season: at least 196 days in 9 of 10 years, 216 days in half of years and 239 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: Kennewick (USC00454154), 3.7 miles from the city center, 390 feet, 27 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension wrote its vegetable planting guide for Colorado, so these dates are a simple starting point for Kennewick[6]. We use the NOAA median last frost (March 28) as the average last frost[6]. Hardy vegetables such as broccoli, lettuce, peas and spinach can go in as early as 2 to 4 weeks before it, which is February 28 to March 14[6]. Semi-hardy vegetables such as beets, carrots and potatoes can go in as early as 2 weeks before it, which is March 14[9]. Tender vegetables such as snap beans and sweet corn can start from seed around March 28[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after it, so the earliest start is April 11[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (March 28) is February 28 to March 14[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (March 28) is March 14, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, March 28[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (March 28), is April 11[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Feb 28 May 4 (from transplants)
Cabbage (hardy)[12] Feb 28 May 24 (from transplants)
Kohlrabi (hardy)[12] Feb 28 Apr 19
Lettuce (hardy)[12] Feb 28 Apr 29
Onions (hardy)[12] Feb 28 Jun 18
Peas (hardy)[12] Feb 28 May 4
Radishes (hardy)[12] Feb 28 Mar 30
Spinach (hardy)[12] Feb 28 Apr 9
Turnips (hardy)[12] Feb 28 Apr 19
Beets (semi-hardy)[12] Mar 14 May 13
Carrots (semi-hardy)[12] Mar 14 May 23
Cauliflower (semi-hardy)[12] Mar 14 not listed
Parsnips (semi-hardy)[12] Mar 14 May 23
Potatoes (semi-hardy)[12] Mar 14 Jul 17
Swiss chard (semi-hardy)[12] Mar 14 May 13
Snap beans (tender)[12] Mar 28 May 27
Sweet corn (tender)[12] Mar 28 May 27
Cucumbers (tender)[12] Mar 28 May 22
Summer squash (tender)[12] Mar 28 May 17
Cantaloupe (very tender)[12] Apr 11 Jul 5
Eggplant (very tender)[12] Apr 11 Jun 10 (from transplants)
Peppers (very tender)[12] Apr 11 Jun 20 (from transplants)
Tomatoes (very tender)[12] Apr 11 Jun 15 (from transplants)
Winter squash (very tender)[12] Apr 11 Jul 20
Watermelon (very tender)[12] Apr 11 Jul 5
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 7b means the average coldest night of the winter is 5°F to 10°F, based on 1991 to 2020[1]. The USDA zone is not about summer heat or frost dates[14]. It helps gardeners judge which perennial plants are most likely to thrive[14]. All of Kennewick's land area, across 4 ZIP code areas, is rated zone 7b[15].

Zone 7b: average annual extreme minimum temperature 5°F to 10°F (1991 to 2020)[1]. Modeled value at the city center: 6.3°F[1].

Share of the city's land area by ZIP code zone: zone 7b 100%[15].

All towns in zone 7b and what zone 7b means

Zone by ZIP code
ZIP code Zone Coldest night range
99336[15] 7b 5 to 10°F
99337[15] 7b 5 to 10°F
99338[15] 7b 5 to 10°F
99352[15] 7b 5 to 10°F

Questions people ask

What growing zone is Kennewick, Washington?
The 2023 USDA map puts the center of Kennewick in zone 7b[1]. All of the city's land area is in ZIP code areas rated 7b[15].
When is the last frost in Kennewick?
The median last spring frost is March 28, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after April 10[2].
When to plant tomatoes in Kennewick?
CSU Extension says tomatoes typically go in 2 or more weeks after the average last frost, which gives an earliest start of April 11[11]. CSU wrote its guide for Colorado[6].
When is the first frost in Kennewick?
The median first fall frost is October 30[3]. In 1 of 10 years it comes before October 18[3].
How long is the growing season in Kennewick?
The season between the last spring and first fall frost is at least 216 days in half of years[4]. It is at least 196 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Kennewick, Washington in zone 7b. Zone 7b means an average annual extreme minimum temperature of 5°F to 10°F over 1991 to 2020. The map's modeled value at the city center is 6.3°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 9, in half of years after March 28, and in 1 of 10 years after April 10 (NOAA 1991 to 2020 normals). The median last frost date is March 28. 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 18, in half of years before October 30, and in 9 of 10 years before November 15 (NOAA 1991 to 2020 normals). The median first frost date is October 30. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 196 days in 9 of 10 years, at least 216 days in half of years, and at least 239 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Kennewick weather station (USC00454154), 3.7 miles from the center of Kennewick at 390 feet, using 27 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 8 and the median first fall date is November 11. 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. Kennewick, Washington overlaps 4 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 7b. 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.