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Frost dates and planting calendar for Dover, New Hampshire

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

USDA hardiness zone
6a[1]
Median last spring frost
May 8[2]
Median first fall frost
Oct 4[3]
Growing season, median
148 days[4]

Dover, New Hampshire is in USDA hardiness zone 6a[1]. The median last spring frost is May 8, which means a last frost after that date in half of years[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Apr 27, half of years May 8, 1 in 10 years after May 22Last frostmedian May 8First fall frost: 9 in 10 years before Oct 20, half of years Oct 4, 1 in 10 years before Sep 23First frostmedian Oct 4Frost riskHardyHardy vegetables: plant Apr 10 to Apr 24Apr 10 to Apr 24Semi-hardySemi-hardy vegetables: plant Apr 24 to May 8Apr 24 to May 8TenderTender vegetables: plant around May 8around May 8Very tenderVery tender vegetables: plant from May 22from May 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 for Dover come from the Durham weather station, using records from 1991 to 2020[5]. In 9 of 10 years the last spring frost comes after April 27, and in 1 of 10 years it comes after May 22[2]. In the fall, the first frost comes before October 4 in half of years, and before October 20 in 9 of 10 years[3]. These are chances from past records, not a forecast, so any year can come earlier or later[5].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after April 27 after May 8 after May 22
First fall frost (32°F)[3] before September 23 before October 4 before October 20
  • Hard freeze (28°F): median last spring date April 27, median first fall date October 15[7].
  • Frost-free growing season: at least 131 days in 9 of 10 years, 148 days in half of years and 164 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: Durham (USC00272174), 4.5 miles from the city center, 75 feet, 27 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension's planting guide was written for Colorado, so these dates are a simple calculation and not local advice[6]. Hardy vegetables such as lettuce, peas and spinach can go in as early as 2 to 4 weeks before the median last frost, which is April 10 to April 24[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before it, from April 24[9]. Tender vegetables such as snap beans and sweet corn can be sown from seed around May 8[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 May 22[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (May 8) is April 10 to April 24[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (May 8) is April 24, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, May 8[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (May 8), is May 22[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Apr 10 Jun 14 (from transplants)
Cabbage (hardy)[12] Apr 10 Jul 4 (from transplants)
Kohlrabi (hardy)[12] Apr 10 May 30
Lettuce (hardy)[12] Apr 10 Jun 9
Onions (hardy)[12] Apr 10 Jul 29
Peas (hardy)[12] Apr 10 Jun 14
Radishes (hardy)[12] Apr 10 May 10
Spinach (hardy)[12] Apr 10 May 20
Turnips (hardy)[12] Apr 10 May 30
Beets (semi-hardy)[12] Apr 24 Jun 23
Carrots (semi-hardy)[12] Apr 24 Jul 3
Cauliflower (semi-hardy)[12] Apr 24 not listed
Parsnips (semi-hardy)[12] Apr 24 Jul 3
Potatoes (semi-hardy)[12] Apr 24 Aug 27
Swiss chard (semi-hardy)[12] Apr 24 Jun 23
Snap beans (tender)[12] May 8 Jul 7
Sweet corn (tender)[12] May 8 Jul 7
Cucumbers (tender)[12] May 8 Jul 2
Summer squash (tender)[12] May 8 Jun 27
Cantaloupe (very tender)[12] May 22 Aug 15
Eggplant (very tender)[12] May 22 Jul 21 (from transplants)
Peppers (very tender)[12] May 22 Jul 31 (from transplants)
Tomatoes (very tender)[12] May 22 Jul 26 (from transplants)
Winter squash (very tender)[12] May 22 Aug 30
Watermelon (very tender)[12] May 22 Aug 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

The zone number comes from the average coldest night of each winter from 1991 to 2020, not from summer heat or frost dates[14]. For the center of Dover, the USDA map shows zone 6a[1]. Both ZIP code areas that overlap Dover are rated zone 6a, so the city does not span more than one zone by this count[15].

Zone 6a: average annual extreme minimum temperature -10°F to -5°F (1991 to 2020)[1]. Modeled value at the city center: -8.2°F[1].

Share of the city's land area by ZIP code zone: zone 6a 100%[15].

All towns in zone 6a and what zone 6a means

Zone by ZIP code
ZIP code Zone Coldest night range
03820[15] 6a -10 to -5°F
03823[15] 6a -10 to -5°F

Questions people ask

What growing zone is Dover, New Hampshire?
Dover is in USDA zone 6a on the 2023 map[1]. All of its land area lies in ZIP code areas rated 6a[15].
When is the last frost in Dover?
The median last spring frost is May 8, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after May 22[2].
When is the first frost in Dover?
The median first fall frost is October 4, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before September 23[3].
When to plant tomatoes in Dover?
CSU Extension says very tender vegetables like tomatoes typically go in 2 or more weeks after the average last spring frost[11]. Using the Dover median last frost, the earliest start is May 22[11].
How long is the growing season in Dover?
The growing season between the last spring and first fall frost is at least 148 days in half of years[4]. It is at least 131 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Dover, New Hampshire in zone 6a. Zone 6a means an average annual extreme minimum temperature of -10°F to -5°F over 1991 to 2020. The map's modeled value at the city center is minus 8.2°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 April 27, in half of years after May 8, and in 1 of 10 years after May 22 (NOAA 1991 to 2020 normals). The median last frost date is May 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 September 23, in half of years before October 4, and in 9 of 10 years before October 20 (NOAA 1991 to 2020 normals). The median first frost date is October 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 131 days in 9 of 10 years, at least 148 days in half of years, and at least 164 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Durham weather station (USC00272174), 4.5 miles from the center of Dover at 75 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 April 27 and the median first fall date is October 15. 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. Dover, New Hampshire overlaps 2 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 6a. 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.